JP2012022363A - Inner product calculation device and inner product calculation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inner product calculation device and an inner product calculation method realizing a high-speed computing having cycle time suitable for a highly parallel computing with a computing unit constitution that has a small hardware amount and uses no multiplier, and allowing an inner product calculation to be performed with efficiently and accuracy even using no ROM.SOLUTION: An inner product calculation device comprises: input element registers 2 for storing plural input vector elements; a barrel shifter 3 for calculating the partial product of the term of a power of two of a constant vector element and an input vector element; an adder-subtracter 4 for accumulating the partial products; an accumulator 5 for storing the accumulation result of the adder-subtracter; a shifter 6 for rounding off a result during the accumulation stored in the accumulator 5; and calculation control means for allowing accumulation of the partial products of the terms of the least significant power of two of the constant vector elements and all input vector elements corresponding to the respective terms, sequential repetitive accumulation of the partial products corresponding to the terms of a higher order power of two, and repetition until the terms of the most significant power of two.

Description

  The present invention relates to an inner product calculation device and inner product calculation method for calculating a vector inner product performed in orthogonal transformation such as discrete cosine transformation.

  Vector inner product operation is the core of orthogonal transformation represented by discrete cosine transformation, which is frequently used in the field of image compression processing, etc., but the amount of computation is enormous. In order to respond, generally a large amount of hardware is required, and the cost of the apparatus tends to increase. A discrete cosine transform (hereinafter referred to as DCT) process to which the inner product operation is applied will be briefly described below. The following formula is a general formula of Nth-order DCT for a one-dimensional number sequence.

  The 8th-order DCT processing in which the above equation is N = 8 is expressed by the following matrix product equation.

  The matrix on the right side of this equation is referred to as a DCT coefficient matrix.

  In order to process such a determinant by a digital hardware arithmetic unit, for example, when expressed by a positive / negative sign and an integer of 10-bit digits for fixed-point arithmetic, the following integer determinant is obtained.

  There are many 8th order DCT processes for planar image signals as in the above formula. For example, DCT used in the JPEG (Joint Photographic Experts Group) system is 8 × 8 pixels of 8 pixels in the horizontal direction and 8 pixels in the vertical direction. It is employed as a so-called two-dimensional DCT in which a one-dimensional DCT in the vertical direction is applied and then a one-dimensional DCT in the horizontal direction is applied to decompose the frequency components on an 8 × 8 two-dimensional plane. Hereinafter, for ease of explanation, the elements of the input vector are assumed to be a general 8-bit integer value as a pixel value, and the DCT coefficient is assumed to be a fixed-point representation of about 8 to 16 bits as a typical hardware configuration.

  Here, in Expression 4, when attention is paid to the calculation of Z1 which is an element of the output vector Z, partial row vectors (502, 426, 284, 100, −100, −284, surrounded by the frame of the second row of the DCT coefficient matrix). −426, −502) and the inner product operation of the input vector (X0, X1, X2, X3, X4, X5, X6, X7), 8 multiplications and 7 additions / subtractions are required. As described above, the inner product calculation includes many multiplications and additions, has a large calculation amount, and a lot of hardware has been devised for high-speed processing.

  FIG. 15 shows an example of a conventional inner product calculation device. An inner product arithmetic device 100 shown in FIG. 15 includes adders / subtracters 101, 102, 103, 104, registers 105, 106, 107, 108, multipliers 109, 110, 111, 112, a parallel adder 113, I have.

  15 performs multiplication of each element of the input vector X and the DCT coefficient in parallel for each element of the input vector X by the multipliers 109, 110, 111, and 112, and adds each multiplication result in parallel. An inner product operation is executed by summing the data in the unit 113. Elements X0 to X7 of the input vector are input to the respective multipliers 109, 110, 111, and 112 in parallel, and the DCT coefficient is a constant, so it is placed in a register and is input to the multipliers 109, 110, 111, and 112. Entered. The DCT coefficient may be stored in the ROM.

  Here, assuming that the partial row vector of the DCT coefficient matrix for the inner product is (C0, C1, C2, C3, C4, C5, C6, C7), C0 and C7, C1 and C6, C2 and C5 due to the nature of the DCT coefficient. Since the absolute values of C3 and C4 have a symmetric relationship, the addition or subtraction of the elements of the input X corresponding to the symmetric coefficient, that is, X0 and X7, X1 and X6, X2 and X5, and X3 and X4, is used as the sign of the coefficient. In addition, by performing first (butterfly calculation), the hardware configuration is obtained by reducing the number of multiplications to four.

  However, it is essential that the above-described configuration requires a plurality of multipliers corresponding to the number of multiplications. The multiplier generally has a large hardware scale, consumes a large number of elements, circuit area, and consumes a large amount of power. As the number of digits increases, there is a problem that the cycle time decreases due to propagation delay in the circuit. In order to speed up the processing, it is possible to construct a computing unit configuration in which multiple inner product results can be executed in parallel by multiple inner product computing units, but the hardware scale of each computing unit Is large, the silicon area and the electronic printed circuit board area, which are hardware resources, are finite and require miniaturization, which makes it difficult to parallelize on a large scale. Furthermore, if there are restrictions on the number of digits in the multiplier or adder / subtracter due to circuit size restrictions, it is necessary to round the input digit or the product term multiplication result, and the part from the true lower digit There is a drawback in that accumulation of products is not performed and calculation accuracy is lowered.

  Further, as an inner product calculation device that does not use a multiplier, for example, those described in Patent Documents 1 and 2 have been proposed. FIG. 16 shows an example of an inner product calculation device that does not use a multiplier. The inner product arithmetic device 200 shown in FIG. 16 includes a ROM 201, an adder / subtracter 202, an accumulator 203, and a shifter 204.

  In the inner product calculation device 200 shown in FIG. 16, A to D are input vector elements having a 4-bit width, and the constant vector elements C0 to C3 have a 16-bit width. In the inner product calculation device 200, each element of the constant vector is a fixed value, and therefore, in the inner product calculation with the input vector, the input vector is 4 bits wide, so this is expressed as b3, b2, b1, b0 and a binary value. Is represented by A (b0), B (b0), C (b0), and D (b0), and the partial inner product corresponding thereto is C0 × A (b0) + C1 ×. B (b0) + C2 × C (b0) + C3 × D (b0).

  Since A (b0), B (b0), C (b0), and D (b0) each take only a binary value of 1 or 0, the partial inner product for the bit slice results in a simple addition / subtraction of C0 to C3. To do. Since C0 to C3 are constant vectors of fixed values, the partial inner product calculated in advance is stored in the ROM 201 in accordance with the appearance pattern of the bit slices A (b0), B (b0), C (b0), and D (b0). In the calculation, the partial inner product can be read by reading the ROM 201 from the bit pattern of the bit slice of the input vector. This is called a ROM accumulator and is abbreviated as RAC. In the inner product operation, the inner product operation is achieved by accumulating partial inner products starting from the lowest bit slice and moving upward. The accumulation of the partial inner product is performed by the adder / subtractor 202 and the accumulator 203, and the accumulator 203 is shifted to the right by the shifter 204 to start accumulation of the upper digits.

  In the inner product arithmetic device 200 shown in FIG. 16, the inner product operation can be realized by shift and addition / subtraction, the amount of hardware is small, the operation of the partial inner product is ROMized as a RAC, and it operates at high speed. Since the partial inner product of digits is accumulated in order, the word length of the calculator can be selected according to the required accuracy of the result, and even if it is composed of digits smaller than the operation word length of multiplication, Since the accumulation of the partial inner product is completed, there is an advantage that the calculation accuracy is ensured.

  As described above, the product-sum operation apparatus having the conventional dedicated multiplication circuit, adder / subtractor, and accumulator has a problem that the circuit amount of the multiplication circuit increases and the cost increases. Especially when the multiplication circuit has an array type multiplier, the circuit contents are complicated, regularity is lowered, and the amount of hardware is large, so that a plurality of arithmetic units are configured in parallel on a large scale. It has been difficult to select a SIMD (Single Instruction-stream Multiple Data-stream) arithmetic unit configuration. In addition, since the multiplication circuit is complicated and large-scale in the device having the multiplication circuit, there is a problem that the signal propagation time is increased and the cycle time of the entire arithmetic device is lowered. In addition, the number of arithmetic digits is limited when a small arithmetic block is configured in a large scale and highly parallel to configure an inner product arithmetic device, or when an inner product arithmetic is programmed with an arithmetic device such as a predetermined microprocessor. Therefore, there is a problem that the precision of the inner product operation is reduced because the number of digits of the input itself is reduced or the multiplication result of the product term is rounded to limit the operation digits in the middle. .

  In addition, the inner product arithmetic unit that performs the inner product operation by cumulative addition / subtraction of partial inner product and shift operation using ROM accumulator is a structure that accumulates the partial inner product in order from the lower digit, so all the calculation accuracy of the product term is guaranteed. However, the accuracy of the inner product calculation is not lowered, but the ROM capacity of the ROM accumulator increases as the number of input word lengths and the number of vector elements, that is, the number of product terms increase. there were. This has the problem that, when a large-scale parallel computing unit is configured, the same ROM must be duplicated many times, the utilization efficiency of the hardware area is poor, and the scale of parallelization is limited.

  The present invention aims to solve such problems.

  That is, according to the present invention, it is possible to increase the cycle time by using an arithmetic unit configuration that does not use a multiplier and has a small amount of hardware, and is suitable for high parallelism. An object of the present invention is to provide an inner product calculation device and inner product calculation method.

  In order to solve the above-mentioned problem, the invention described in claim 1 includes an input vector composed of a plurality of input vector elements having a predetermined bit word length and a constant vector composed of a plurality of constant vector elements. In the inner product calculation device for calculating the inner product of the constants, the storage means for storing the plurality of input vector elements, the input vector element is selected from the storage means, and the selected input vector is left bit shifted to shift the constant A shift means for obtaining a partial product of a power-of-two term of a vector element and an input vector element, and accumulating the partial product obtained by the shift means and multiplying the input vector element and the constant vector element. Stores the addition / subtraction means configured with a smaller number of bit digits than the required multiplication precision, and the accumulation result of the addition / subtraction means. An accumulator; a rounding means for rounding a result of operation by truncating a result stored in the accumulator during accumulation by the addition / subtraction means by a bit shift of a predetermined number of digits; and the constant vector The accumulation of the partial products of all the input vector elements related to the same term of the least significant 2 power term of the element is performed and stored in the accumulator. The accumulation is repeated until the most significant power-of-two term is repeated, and before the addition / subtraction means overflows, the rounding means truncates the lower digits of the result stored in the accumulator during the calculation. And an arithmetic control unit that operates so as to obtain an initial value for subsequent accumulation.

  According to a second aspect of the present invention, in the first aspect of the present invention, the calculation control unit is configured to perform the shift unit based on a predetermined table for each two bits of the input vector element. The partial product is obtained, and the addition / subtraction means accumulates the partial product.

  The invention described in claim 3 is the invention described in claim 1 or 2, wherein the rounding means truncates the result stored in the accumulator during accumulation by the addition / subtraction means. It is predetermined as the number of bit digits less than or equal to the number obtained by subtracting the logarithm of the bit vector length of the input vector element and the number of the input vector elements from 2 from the bit word length of the addition / subtraction means It is.

  The invention described in claim 4 is an inner product calculation device for obtaining an inner product of an input vector composed of a plurality of input vector elements having a predetermined bit word length and a constant vector composed of a plurality of constant vector elements. A storage unit that stores the plurality of input vector elements; and the input vector element is selected from the storage unit to obtain a partial product of the power vector of the constant vector element and the selected input vector element Accumulating and adding / subtracting means configured with a bit number smaller than the multiplication precision required when multiplying the input vector element and the constant vector element, and the accumulated result of the adding / subtracting means An accumulator to be stored on the digit side, and the contents of the accumulator are right-bit shifted in the lower digit direction to obtain an accumulated value thereafter, and A first shift means configured with a bit number smaller than the multiplication precision required when multiplying the force vector element and the constant vector element; and the adder / subtracter with 2 of the same digit of the constant vector element. An operation for accumulating partial products of all input vector elements related to the same term of a power term and storing the result in the accumulator, and causing the first shift means to shift the accumulation result stored in the accumulator to the right bit And an arithmetic control unit that repeats up to the most significant digit of the power-of-two term of the constant vector element.

  The invention described in claim 5 is the invention described in claim 4, further comprising second shift means for doubling the input vector element stored in the storage means, wherein the arithmetic control means is predetermined. On the basis of the table, the input vector element stored in the storage means or the input vector element doubled by the second shift means is selected and accumulated in the addition / subtraction means, and the first The shift means is shifted by 2 bits.

  The invention described in claim 6 is a storage means for storing an input vector composed of a plurality of input vector elements having a predetermined bit word length, and a plurality of constant vector elements by left-bit shifting the input vector. Shift means for obtaining a partial product of a power vector of a constant vector composed of 2 and the input vector element, accumulating the partial product obtained by the shift means, and the input vector element and the constant vector element Addition / subtraction means configured with a bit number smaller than the multiplication precision required when multiplying and an accumulator for storing the accumulation result of the addition / subtraction means, and adding / subtracting and shifting of operands in a microprocessor An inner product calculation method for obtaining an inner product of the input vector and the constant vector using an instruction that can be executed integrally. The shift means selects the input vector element from the storage means and obtains the partial product, and the addition / subtraction means takes the same term of the least significant power of 2 of the constant vector element. A second step in which the partial products of all the input vector elements are accumulated and stored in the accumulator; and in the middle of the calculation that is stored in the accumulator before the adder / subtracter overflows A third step of truncating the lower digit of the result stored in the accumulator and setting it as an initial value for subsequent accumulation, wherein the first step and the second step are sequentially raised to a power of 2 The partial product accumulation for the term is repeated until the highest power term of 2 is repeated, and at least the third step is performed at least once during the repetition of the first step and the second step. It is the inner product calculation method comprising.

  The invention described in claim 7 is the invention described in claim 6, wherein the first step selects either the input vector element itself or a value twice as large as the input vector element. The partial product is obtained, and the second step is characterized in that the partial product is accumulated every two bits.

  The invention described in claim 8 is the invention according to claim 6 or 7, wherein the number of bit digits for rounding down the result stored in the accumulator during the accumulation by the addition / subtraction means in the third step is The number of bit digits is less than or equal to the number obtained by subtracting the logarithm of the bit vector length of the input vector element and the number of the input vector elements from 2 from the bit word length of the adding / subtracting means. Is.

  According to the first aspect of the present invention, since the apparatus is constituted by the cumulative addition / subtraction structure having the addition / subtraction means, the accumulator, and the shift means without using the multiplication circuit, the hardware having high regularity and suitable for high parallelism is provided. A computing device with a small amount of wear can be configured. In addition, partial product accumulation is executed in order from the lower digit, and the partial product sum result of the following digits is always reflected in the upper digit, so that the inner product operation can be performed without lowering the operation accuracy. In addition, the accumulator contents can be right-shifted and rounded by the rounding means during accumulation, so even with adder / subtracters and accumulators with a number of digits smaller than the product term multiplication word length, accuracy is reduced without causing overflow. It is possible to perform an inner product operation without any.

  According to the second aspect of the present invention, the operation control means can apply Booth's algorithm to accumulate partial products for every 2 bits of the constant vector, thereby reducing the control step, and Calculation can be performed with a small number of cycles.

  According to the third aspect of the present invention, even if the adder / subtracter and the accumulator have a number of digits smaller than the multiplication word length of the product term, it is possible to perform the inner product operation without causing overflow.

  According to the fourth aspect of the present invention, since the apparatus is configured by the cumulative addition / subtraction structure having the addition / subtraction means, the accumulator, and the shift means without using the multiplication circuit, the hardware having high regularity and suitable for high parallelism is provided. A computing device with a small amount of wear can be configured. Also, since the partial product accumulation is performed in order from the lower digit, the result of the partial product sum of the lower digit is always completed and reflected in the upper digit, so that the inner product calculation can be performed without lowering the calculation accuracy. it can. In addition, since the contents of the accumulator can be right-shifted and rounded during accumulation, even an arithmetic unit having an adder / subtracter and an accumulator with a number of digits smaller than the multiplication word length of the product term does not cause overflow. It is possible to perform an inner product calculation without degrading accuracy. Furthermore, since there is no barrel shifter for shifting the input to the left by an arbitrary digit, the circuit scale can be further reduced.

  According to the fifth aspect of the present invention, the operation control means can apply the Booth algorithm to accumulate the partial products for every 2 bits of the constant vector, thereby reducing the control steps and further reducing the number of control steps. It can be calculated by the number of cycles.

  According to the sixth aspect of the present invention, in a microprocessor having an addition / subtraction instruction in which operand shifts are integrated, partial product accumulation is executed in order from the lower digit, so that the partial product of the following digits is always added to the upper digit. Since the sum result is completed and reflected, the inner product calculation can be performed without lowering the calculation accuracy. In addition, since it has a third step of rounding the contents of the accumulator right-shifted during accumulation, the arithmetic unit having an adder / subtracter and accumulator with a number of digits smaller than the multiplication word length of the product term does not cause overflow. It is possible to provide a method capable of performing an inner product operation without a decrease in accuracy.

  According to the seventh aspect of the present invention, since the Booth algorithm is applied to accumulate the partial products for every two bits of the constant vector, the number of partial products to be accumulated is reduced and the number of executed instructions is reduced. Can be further reduced.

  According to the eighth aspect of the present invention, even if the arithmetic unit includes an adder / subtracter having a number of digits smaller than the multiplication word length of the product term and an accumulator, the inner product operation can be performed without causing overflow. it can.

It is a lineblock diagram of the inner product arithmetic unit concerning a 1st embodiment of the present invention. 3 is a program list showing an inner product operation of the inner product operation device shown in FIG. 1. It is a booth algorithm table | surface applied to the inner product calculating apparatus concerning the 2nd Embodiment of this invention. It is a program list | wrist which showed the inner product calculation operation | movement of the inner product calculation apparatus concerning the 2nd Embodiment of this invention. It is a block diagram of the inner product calculating apparatus concerning the 3rd Embodiment of this invention. 6 is a program list showing an inner product operation of the inner product operation device shown in FIG. 5. It is a block diagram of the inner product calculating apparatus concerning the 4th Embodiment of this invention. 8 is a program list showing an inner product operation of the inner product operation device shown in FIG. 7. It is a block diagram of the calculating part of the microprocessor which performs the inner product calculating method concerning the 5th Embodiment of this invention. It is a machine language instruction code format of the microprocessor shown in FIG. FIG. 10 is a part of a program list showing an inner product calculation operation of the microprocessor shown in FIG. 9. FIG. FIG. 10 is another part of the program list showing the inner product calculation operation of the microprocessor shown in FIG. 9. FIG. 10 is a flowchart of an inner product calculation method operating on the microprocessor illustrated in FIG. 9. It is a program list | wrist which showed the inner product calculation operation | movement of the microprocessor concerning the 6th Embodiment of this invention. It is the block diagram which showed the conventional inner product calculating apparatus. It is the block diagram which showed the conventional inner product calculating apparatus.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 is a configuration diagram of an inner product arithmetic device according to a first embodiment of the present invention. FIG. 2 is a program list showing the inner product calculation operation of the inner product calculation apparatus shown in FIG.

  FIG. 1 shows an inner product calculation device 1 according to a first embodiment of the present invention. 1 includes an input element register 2, a barrel shifter 3, an adder / subtracter 4, an accumulator 5, a shifter 6, a selector 7, and a control unit 8.

  The input element register 2 as storage means is composed of eight registers R0 to R7 having an 8-bit word length. Input vector elements (for example, X0 to X7 in Formula 4) are stored in each register, and one register is selected by a control signal from the control unit 8 and output to the barrel shifter 3.

  The barrel shifter 3 as a shift means shifts the input vector element inputted to the left by an arbitrary number of digits, and is connected to one input of the adder / subtractor 4. In this embodiment, it has a left shift function with an input 8-bit output 16-bit word length and 0 to 9-bit digit sign extension. The shift amount of the barrel shifter 3 is selected for each cycle by a control signal from the control unit 8.

  The adder / subtracter 4 as addition / subtraction means is an arithmetic unit having a word length of 16 bits for both input and output, in which an operation of addition or subtraction is selected for each cycle by a control signal from the control unit 8. That is, the number of bit digits is smaller than the multiplication accuracy required when the input vector element and the constant vector element are multiplied. The output of the adder / subtractor 4 is connected to the accumulator 5.

  The accumulator 5 is a 16-bit register in which intermediate and final calculation results by the adder / subtracter 4 are stored. The output of the accumulator 5 is connected to the shifter 6.

  The shifter 6 serving as a rounding means shifts the arithmetic result stored in the accumulator 5 to the right by a 5-bit fixed digit by a control signal from the control unit 8 and rounds off the intermediate result of the arithmetic operation. It has a configuration that can.

  The selector 7 selects the output of the shifter 6 and the output of the accumulator 5 according to a control signal from the control unit 8 and is connected to the other input of the adder / subtractor 4 and outputs the result as an operation result to the outside.

  The control unit 8 serving as an arithmetic control means controls the arithmetic operation of the inner product arithmetic device 1 and outputs control signals according to the arithmetic operation steps to the input element register 2, the barrel shifter 3, the adder / subtractor 4, the accumulator 5, the shifter 6, and the selector. 7 is output.

  The inner product calculation device 1 having the above-described configuration includes an input element register 2 having a register for storing a plurality of input vector elements and means for selecting the same in order to perform a vector inner product calculation, and has a number of digits smaller than the multiplication word length. An adder / subtracter 4 is further provided, and a shifter 6 is provided for truncating the lower digits that are no longer needed after the accumulation is completed so that the addition / subtraction operation does not overflow during the accumulation of partial products.

  Next, the contents of the product-sum operation (inner product operation) of the inner product operation device 1 described above will be described.

  For example, the inner product operation of the input vector elements X0, X1, X2,... X7 represented by the signed 8-bit and the constant vector elements C0, C1, C2,. Explain how. The constant vector corresponds to a cosine coefficient for DCT processing. Hereinafter, an inner product calculation method of the output element Z1 of the integer determinant representing the DCT process of Formula 4 will be described as an example.

The following numerical values are obtained by extracting the second row vector (the second row of Equation 4) of the DCT coefficient matrix expressed in 10-bit fixed-point representation and expressing the integer value, sign, and absolute value in binary.
C0 = 502 (+) 1_1111_1010
C1 = 426 (+) 1 — 1010 — 1010
C2 = 284 (+) 1_0001_1100
C3 = 100 (+) 0 — 0110 — 0100
C4 = −100 (−) 0 — 0110 — 0100
C5 = −284 (−) 1 — 0001 — 1100
C6 = −426 (−) 1 — 1010 — 1010
C7 = −502 (−) 1 — 1111 — 0110

  These absolute values are expressed as follows in terms of a power-of-two polynomial (in the following equations, * indicates multiplication, and 2 ^ 1 indicates 2 to the power of 1).

  Where the vector dot product Z is generally

  Z1 which is the second element of the output vector of the DCT result is obtained by the following equation.

  The multiplication of 502 * X0 in the above formula is

  When this is expanded,

  It becomes.

  2 ^ 1 * X0 represents the partial product of the 2nd power term of the constant “502”, 2 ^ 4 * X0 represents the partial product of the 4th power of the constant “502”, and the most significant digit of the constant “502” The result of multiplication of 502 * X0 is obtained by adding up to the partial product of 2 8 terms.

  That is, since each partial product is a power of 2 of X0, it can be obtained simply by the left shift operation of the data, and the result of multiplication is obtained by accumulating them by the adder / subtractor 4. This is the principle of product-sum operation by subsequent shift and addition / subtraction. Items other than 502 * X0 are also described below.

  FIG. 2 shows a program list of operations for obtaining Z1 in accordance with the principle described above. This program runs on the control unit 8. The left end of FIG. 2 represents a step number (line number), and the right control part represents the actual control content.

  Referring to the program list of FIG. 2, the partial product for bit 1, that is, the first power term of 2, which is the lowest power term of each element of the constant vector, from step 002 to 005 after resetting the accumulator 5 in step 001. Each element of the corresponding input vector is selected and shifted to the left, and cumulative addition / subtraction is sequentially performed every cycle. Since the constant vector elements C0, C1, C2, and C3 are positive numbers and C4, C5, C6, and C7 are negative numbers, the partial products are added or subtracted according to the positive and negative values. At this time, the element of the input vector is selected by the third control term, and the left shift amount by the barrel shifter 3, that is, the input power of 2 is selected by the fourth control term. The second control term represents the selection of addition or subtraction of the adder / subtractor, and plays a role of switching between addition and subtraction according to the sign of the constant vector.

  That is, in this one step, the barrel shifter 3 selects an input vector element from the input element register 2 and shifts the selected input vector to the left by shifting the power vector of the constant vector element 2 and the input vector element. The adder / subtractor 4 accumulates the partial products obtained by the barrel shifter 3 and stores the accumulated result of the adder / subtractor 4 in the accumulator 5.

  Therefore, Steps 002 to 005 are operations of 2 ^ 1 * X0 + 2 ^ 1 * X1 + 2 ^ 1 * X6 + 2 ^ 1 * X7, that is, the rightmost term of each expression of Equation 10 (the least significant power of each element of the constant vector) This indicates that the cumulative addition / subtraction of (item) is being performed. In the constant vector shown in this embodiment, since the 2 0th power term is all “0”, the 2nd power term is calculated as the lowest power term. However, depending on the setting of the constant vector, 2 0 In some cases, the power term is the lowest power term, and in this case, the cumulative addition / subtraction of the 0th power term is performed.

  Next, in steps 006 to 011, a partial product of 2 square terms of each element of the constant vector is generated and cumulative addition / subtraction is performed, and in the following order in steps 012 to 015, partial products of 2 cube terms, steps 016 to From 019, addition and subtraction of partial products of 2 4 terms are performed.

  At this time, since the accumulation result of the accumulator 5 reaches a maximum of 16-bit digits, in order to avoid overflow of subsequent operations, in the next step 020, cumulative addition / subtraction of partial products of the fifth power term is started. At the time of operation, the contents of the accumulator 5 are shifted 5 bits to the right by the shifter 6 in the fifth control term and input to the adder / subtractor 4 so that the lower digits are rounded off by 5 bits of the intermediate accumulation result. Let That is, the result stored in the accumulator 5 in the middle of accumulation by the adder / subtractor 4 is rounded down by a bit shift of a predetermined number of digits to round the calculation result. In order to align the digits of the partial products to be cumulatively added and subtracted, the shift amount of the barrel shift 3 for obtaining a partial product after step 020, that is, the partial vector after the fifth power of the constant vector is started from zero.

  In this way, cumulative addition / subtraction is performed in order starting from the partial product of the lower digits, and the lower digits of the intermediate results that have already been subjected to cumulative addition / subtraction are right-shifted and rounded off so that the addition / subtraction value does not overflow during the calculation. It is the feature. When processing such as DCT, which is used for image compression, is performed with a digital computing unit, the word length of the computing unit is limited, and therefore overflow occurs by rounding off the result of cumulative addition / subtraction. Therefore, it is possible to perform the inner product calculation without degrading accuracy.

  Next, cumulative addition / subtraction of partial products of 2 6 power terms is performed through steps 026 to 029, cumulative addition / subtraction of partial products of 2 7 power terms is performed through steps 030 to 033, and 2 8 powers through steps 034 to 039. Cumulative addition / subtraction of partial products of terms is performed.

  That is, by executing the program list of FIG. 2, the adder / subtracter 4 accumulates the partial products of all the input vector elements related to the same term in the least significant power-of-two term of the constant vector elements, thereby accumulating the accumulator. 5, and thereafter, the partial product accumulation for the higher-order power-of-two term is sequentially repeated until the highest-order power-of-two term is repeated, and the shifter 6 before the overflow of the adder / subtractor 4 occurs. Thus, the lower digit of the result stored in the accumulator 5 in the middle of the calculation is truncated, and the operation is performed so as to be the initial value of the subsequent accumulation.

  In this embodiment, a signed 8-bit input vector and a fixed-point constant (coefficient) vector of 10 bits after the unsigned decimal point are finally used to finally produce a maximum of 11 bits with an integer part signed 5 bits Thus, a 16-bit calculation result is obtained. For example, in the case of a two-dimensional DCT, it is processed as an input of the DCT process in the next stage.

  According to the present embodiment, there is no dedicated multiplier and only the input element register 2, the adder / subtractor 4, the accumulator 5, the barrel shifter 3 and the shifter 6 are provided. Can be configured. Further, since it is assumed that one vector element of the inner product operation is a constant, the inner product operation can be realized only by selecting an input vector element (register) and simple control of the shift amount and addition / subtraction. In addition, in the configuration using the conventional multiplier, the accuracy of addition / subtraction of the maximum word length of the multiplication result is necessary, but by multiplying the partial products of the same digit in order from the lower order, the maximum multiplication is possible. Even with an arithmetic unit configuration having a word length smaller than the word length, it is possible to perform the inner product calculation without lowering the carry from the lower digit accumulation, that is, ensuring the calculation accuracy. In addition, since the contents of the accumulator 5 can be right-shifted and rounded by the shifter 6 during the accumulation, even the adder / subtractor 4 and the accumulator 5 having a number of digits smaller than the multiplication word length of the product term cause overflow. It is possible to perform inner product calculation without any loss of accuracy.

In the present embodiment, in the rounding process of the intermediate calculation result, the arithmetic unit is configured to include a shifter 6 that performs a right shift fixed at 5 bits. The number of digits discarded is calculated as follows. For example, if the word length of the input vector element is 8 bits, the number of vector elements is 8, and the word length of the adder / subtracter is 16 bits, the partial product that can be accumulated without causing overflow is the constant vector element (16 − (8 + log ₂ 8)) + 1 = 6 bits (number obtained by subtracting the logarithm of the bitword length of the input vector element 4 from the bitword length of the input vector element and the number of input vector elements 2) The following number of bit digits). In other words, accumulation up to a partial product corresponding to a maximum of 6 bits of a constant vector element can be performed without overflow, and at that point, the lower digits up to 6 bits that have already been accumulated are truncated. Is possible. However, in this embodiment, the maximum word length of 16 bits (integer part 11 bits, decimal part 5 bits) is output in order to reduce the precision truncation of the inner product operation as much as possible. The 5-bit fixed digit truncation is executed after the accumulation of partial products corresponding to 5 bits of constant vector elements is completed. By previously determining the number of rounding digits, the intermediate accumulation result can be truncated using only the fixed-digit shifter 6 without using an arbitrary-digit barrel shifter having a large hardware scale. .

(Second Embodiment)
Next, a second embodiment of the present invention will be described with reference to FIGS. Note that the same parts as those in the first embodiment described above are denoted by the same reference numerals and description thereof is omitted. FIG. 3 is a booth algorithm table applied to the inner product arithmetic device according to the second embodiment of the present invention. FIG. 4 is a program list showing an inner product operation of the inner product operation device according to the second embodiment of the present invention.

  This embodiment has the same configuration as that of the first embodiment, but changes the control of the inner product operation to reduce the number of cycles. In this embodiment, by applying the second order Booth algorithm and generating partial products for every 2 bits of the constant vector element, the number of partial products to be accumulated can be reduced, and higher speed operation can be performed. .

  In the second-order Booth algorithm, each of the multipliers is expressed as b9, b8, b7, b6, b5, b4, b3, b2, b1, b0 with a constant vector element as a multiplier. Rather than finding a partial product with a multiplicand that is an input vector element for each power of 2 that is a bit, a partial product of (b1, b0) from the lower order, that is, a partial product of (b1, b0), (b3, b2) In this method, the partial product, the partial product of (b5, b4), the partial product of (b7, b6), and the partial product of (b9, b8) are obtained in order. However, for example, in the case of (b1, b0) = (1, 1), the partial product is three times the multiplicand, and an additional adder is required. In order to avoid this, according to the table shown in FIG. Replace with generation of partial product of power of 2.

  3 bits of the multiplier shown in FIG. 3 are (b1, b0, “0”) for the least significant digit, (b3, b2, b1), (b5, b4, b3), (b7, The bit values of b6, b5) and (b9, b8, b7) are shown. Further, “M” of the partial product to be added indicates the multiplicand itself, and “2M” indicates a value obtained by doubling the multiplicand, that is, a one-bit left shift.

  By the way, in Booth's algorithm, only the number of partial products to be added / subtracted is subtracted, and since the multiplier side is a constant, the partial products to be added / subtracted are known in advance. In the case of this embodiment, the first embodiment shows In addition to the arithmetic unit configuration, no special hardware is required, and only the partial products to be added and subtracted are different, so that the control step may be changed.

  FIG. 4 shows a program list of the operation of this embodiment. FIG. 4 also shows a case where Z1 of Formula 4 is obtained as in FIG. This program runs on the control unit 8.

Referring to the program list of FIG. 4, in step 001, the accumulator 5 is reset to reset the calculation. Next, Steps 002 to 005 calculate the sum of partial products corresponding to the least significant 2 bits of the constant vector, that is, b1 and b0, that is, the partial inner product. Here, the constant vector elements C0 to C7 are
C0 = 502 (+) 1_1111_1010
C1 = 426 (+) 1 — 1010 — 1010
C2 = 284 (+) 1_0001_1100
C3 = 100 (+) 0 — 0110 — 0100
C4 = −100 (−) 0 — 0110 — 0100
C5 = −284 (−) 1 — 0001 — 1100
C6 = −426 (−) 1 — 1010 — 1010
C7 = −502 (−) 1 — 1111 — 0110
Therefore, referring to the Booth algorithm table shown in FIG. 3 from the bit pattern of (b1, b0, “0”) including the lower 2 bits of each constant vector element and the code of the constant vector element, the partial inner product Perform the operation.

  Therefore, in step 002, the constant vector element C0 is a positive number and (b1, b0, “0”) is “100”, so “−2M”, that is, twice the input element X0 that is a multiplicand is subtracted from FIG. ing. In step 003, since the constant vector element C1 is a positive number and (b1, b0, “0”) is “100”, “−2M”, that is, twice the input element X1 that is a multiplicand is subtracted from FIG. . In step 004, since the constant vector element C6 is a negative number and (b1, b0, “0”) is “100”, “−2M”, that is, twice the input element X6 that is a multiplicand is added from FIG. In step 005, since the constant vector element C7 is a negative number and (b1, b0, “0”) is “100”, “−2M”, that is, twice the input element X7 which is a multiplicand is added. Since the constant vectors C2 to C5 have “b1, b0,“ 0 ”)“ 000 ”, there is no partial product to be added or subtracted. That is, at each step, the barrel shifter 3 obtains a partial product for every two bits of the input vector element, and the adder / subtracter 4 accumulates the partial products.

  Next, steps 006 to 013 calculate the sum of partial products corresponding to the next two bits of the constant vector, that is, b3 and b2, that is, the partial inner product. Here, the position of the partial product is based on the position of b2 which is higher by 2 bits, and the partial product “M” to be added is a value obtained by multiplying the multiplicand by four, that is, the multiplicand is shifted to the left by 2 bits. “2M” is a value obtained by multiplying the multiplicand by eight, that is, a value obtained by shifting the multiplicand to the left by 3 bits.

  Therefore, in step 006, since the constant vector C0 is a positive number and (b3, b2, b1) is “011”, “+ 2M”, that is, eight times the multiplicand input element X0 is added from FIG. In step 007, since the constant vector C1 is a positive number and (b3, b2, b1) is “101”, “−M”, that is, four times the multiplicand input element X1 is subtracted from FIG. In step 008, since the constant vector C2 is a positive number and (b3, b2, b1) is “110”, “−M”, that is, four times the multiplicand input element X2 is subtracted from FIG. In step 009, since the constant vector C3 is a positive number and (b3, b2, b1) is “010”, “+ M”, that is, four times the multiplicand input element X3 is added from FIG. In step 010, the constant vector C4 is a negative number and (b3, b2, b1) is “010”, so that “+ M”, that is, four times the multiplicand input element X4 is subtracted from FIG. In step 011, since the constant vector C5 is a negative number and (b3, b2, b1) is “110”, “−M”, that is, four times the multiplicand input element X5 is added from FIG. In step 012, since the constant vector C6 is a negative number and (b3, b2, b1) is “101”, “−M”, that is, four times the multiplicand input element X6 is added from FIG. In step 013, since the constant vector C7 is a negative number and (b3, b2, b1) is “011”, “+ 2M”, that is, eight times the multiplicand input element X7 is subtracted from FIG.

  Next, steps 014 to 021 are the next 2 bits b5 and b4 of the constant vector, steps 022 to 025 are the next 2 bits b7 and b6 of the constant vector, and steps 026 to 031 are the next 2 bits b9 and b8 of the constant vector. The sum of the partial products corresponding to each is accumulated. Here, in step 018, in order to avoid overflow in the adder / subtractor 4 as in the first embodiment, the lower-order 5 bits fixed round-down process of the intermediate result of accumulation is performed.

  According to this embodiment, the inner product operation is performed by accumulating the partial inner product for every two bits of the constant vector element, so that the number of partial products to be accumulated can be reduced and the control step can be reduced. The number of operation cycles can be further reduced. For example, comparing the first embodiment (FIG. 2) and the present embodiment (FIG. 4), FIG. 2 requires 39 steps, whereas FIG. 4 improves the calculation speed by 31 steps and about 20%. It is clear that

(Third embodiment)
Next, a third embodiment of the present invention will be described with reference to FIGS. The same parts as those in the first and second embodiments described above are denoted by the same reference numerals and description thereof is omitted. FIG. 5 is a block diagram of an inner product calculation device according to the third embodiment of the present invention. FIG. 6 is a program list showing the inner product calculation operation of the inner product calculation apparatus shown in FIG.

  In the present embodiment, the barrel shifter 3 and the selector 7 are deleted from the inner product calculation device 1 shown in FIG. The adder / subtracter 4 becomes an adder / subtracter 9 having an 11-bit word length, and a shifter 10 as a first shift means is provided at the subsequent stage of the accumulator 5.

  The adder / subtractor 9 is an arithmetic unit having one input of 8 bits, the other input of 11 bits, and an output of 11 bits for selecting an operation of addition or subtraction for each cycle by a control signal from the control unit 8. The output of the input element register 2 is connected to one 8-bit input. That is, the number of bit digits is smaller than the multiplication accuracy required when the input vector element and the constant vector element are multiplied.

  The accumulator 5 receives the output of the adder / subtractor 9 as the upper 11 bits, and the lower 5 bits as the lower 5 bits of the shifter 10 described later.

  The shifter 10 has a 16-bit word length, and shifts the operation result stored in the accumulator 5 to the right by a 1-bit fixed digit by a control signal from the control unit 8.

  In the inner product arithmetic device 1 having the above-described configuration, a plurality of input vector elements are stored in the input element register 2, one is selected by the control signal, and is connected to one of the adder / subtractor 9. The adder / subtractor 9 selects an addition or subtraction operation for each cycle according to the control signal. The output of the adder / subtractor 9 is connected to the accumulator 5, and the intermediate and final calculation results are stored. The output of the accumulator 5 is connected to the shifter 10 so as to perform a 1-bit right shift, and the intermediate result stored in the accumulator 5 can be shifted to the right by 1 bit. The shifter 10 does not perform the shift operation while accumulating the partial product of the same digit, and performs the shift operation after the accumulation of the same digit is completed and starts accumulating the upper digit. The presence or absence of the shift operation is switched by a control signal.

  FIG. 6 shows a program list of the operation of this embodiment. FIG. 6 also shows a case where Z1 of Equation 4 is obtained as in FIGS. This program runs on the control unit 8.

  Referring to the program list of FIG. 6, in step 001, the accumulator 5 is reset to reset the calculation. Next, from step 002 to 005, select the partial product for bit 1 that is the lowest power term of each element of the constant vector, that is, the first power term of 2, select each element of the corresponding input vector, and sequentially in each cycle. Cumulative addition / subtraction. Since the output of the adder / subtracter 9 is connected to the upper 11 bits of the accumulator 5, the first accumulation result is obtained with the 6th bit of the accumulator 5 as the least significant bit. Since the constant vector elements C0, C1, C2, and C3 are positive numbers and C4, C5, C6, and C7 are negative numbers, the partial products are added or subtracted according to the positive and negative values. At this time, the element of the input vector is selected by the third control term, and the right shift of the accumulator output is controlled by the fourth control term. The second control term is a term for selecting addition or subtraction by the adder / subtractor 9 and plays a role of switching between addition and subtraction according to the sign of the constant vector element. That is, in this one step, the adder / subtracter 9 accumulates the partial products of all input vector elements related to the same term of the power-of-two term of the same digit of the constant vector element and stores it in the accumulator 5. Yes.

  Next, in step 006, the right shift of the accumulator 5 is selected and input to the adder / subtracter 9 in order to start accumulating the partial product of the upper digits. Cumulative addition / subtraction of partial products of 2 square terms of each element of the constant vector is executed through steps 006 to 011, followed by steps 012 to 015 in the order of 2 3 power terms, and steps 016 to 019 in order of 2 4 power terms. , Partial powers of 2 to the 5th power term from step 020 to 025, 2 to the 6th power term from step 026 to 029, 2 to the 7th power term from step 030 to 033, and 2 to the 8th power term from step 034 to 039 Add and subtract each. In the numerical example of the present embodiment, there is no 2 9 power term. That is, the shifter 10 performs an operation of shifting the accumulation result stored in the accumulator 5 to the right bit, and the operation of accumulating the partial product of the upper digits is repeated up to the most significant digit.

  In steps 040 and 041, the contents of the accumulator 5 are each shifted to the right by 1 bit, and the effective digits are aligned. Finally, an arithmetic result of 16 bits in total is obtained with 11 bits with an integer part sign and 5 bits with a fractional part.

  According to the present embodiment, since there is no individual multiplier but only the input element register 2, the adder / subtractor 9, the accumulator 5, and the shifter 10, the amount of hardware is small and a regular arithmetic device can be configured. Further, since it is assumed that one vector element of the inner product operation is a constant, the inner product operation can be realized only by selecting an input vector element (register) and simple control of the shift amount and addition / subtraction. In addition, in the configuration using the conventional multiplier, the addition / subtraction accuracy of the maximum word length of the multiplication result is necessary. However, the cumulative addition / subtraction is performed in order from the partial product of the lower digits, and exceeds the word length of the accumulator 5. Since the accumulation result in the middle of the right shift is automatically truncated, even if the arithmetic unit has a word length smaller than the maximum word length of multiplication by accumulating partial products of the same digit in order from the lower order, Thus, it is possible to perform the inner product calculation without lowering the carry from the lower digit accumulation, that is, while ensuring the calculation accuracy. Furthermore, since the barrel shifter is not used when obtaining the partial product, the circuit scale can be reduced.

(Fourth embodiment)
Next, a fourth embodiment of the present invention will be described with reference to FIGS. In addition, the same code | symbol is attached | subjected to the same part as the 1st-3rd embodiment mentioned above, and description is abbreviate | omitted. FIG. 7 is a block diagram of an inner product arithmetic device according to the fourth embodiment of the present invention. FIG. 8 is a program list showing the inner product calculation operation of the inner product calculation apparatus shown in FIG.

  This embodiment has the same basic configuration as the third embodiment, but selects whether the output from the input element register 2 is output as it is or twice (1 bit shift) for output. It is configured. Therefore, a shifter 11 as a second shift means with a sign extension function for doubling the output of the input element register 2 and a selector 12 are added, and one input of the adder / subtractor 13 has 9 bits.

  Further, the shifter 14 as the first shift means is changed so as to shift the calculation result stored in the accumulator 5 to the right by a 2-bit fixed digit by a control signal from the control unit 8.

  The basic operation of this embodiment is the same as that of the third embodiment. However, as described in the second embodiment, the second order Booth algorithm is adopted, and the lower order bit is obtained for every two bits of the constant vector element. The partial product to be added or subtracted from the 3-bit pattern to which “” is added, that is, the input vector element itself “M” or its double value “2M” is accumulated. That is, either the input vector element or the input vector element doubled by the shifter 11 is selected and accumulated in the adder / subtractor 13. The generation or selection of itself or the double value is performed by controlling the shifter 11 and the selector 12 for each cycle. When the accumulation of the partial product of the same digit is finished every 2 bits of the constant vector element, the contents of the accumulator 5 are shifted to the right by 2 bits in the shifter 14 to start the accumulation of the upper digit, and the next addition / subtraction input It becomes.

  FIG. 8 shows a program list of the operation of this embodiment. FIG. 8 also shows the case where Z1 of Equation 4 is obtained in the same manner as FIG. 2, FIG. 4, and FIG. This program runs on the control unit 8.

  Referring to the program list of FIG. 8, in step 001, the accumulator 5 is reset to reset the calculation. The booth shown in FIG. 3 as a partial product to be added to or subtracted from 2 bits of bit1 and bit0, that is, the lowest power term of each element of the constant vector from step 002 to 005, that is, the 2nd power term and the 2nd power term. In accordance with the algorithm table, each element of the input vector itself or its double value is cumulatively added or subtracted every cycle. Since the calculation contents are the same as those in the second embodiment, description thereof will be omitted. Since the output of the adder / subtractor 13 is connected to the upper 11 bits of the accumulator 5, the first accumulation result is obtained with the 6th bit of the accumulator 5 as the least significant bit.

  Next, in step 006, the accumulator contents are shifted to the right by the shifter 14 and input to the adder / subtractor 13 in order to start accumulating the partial product of the upper digits of 2 bits according to the Booth algorithm. From steps 006 to 013, cumulative addition / subtraction of partial products of 2 squared terms and 2 cubed terms of each element of the constant vector is executed, and in the order of steps 014 to 021 2 is 4th power terms and 2 to the 5th power. In terms of terms, 2 is the 6th power term and 2 7th power term through steps 022 to 025, and 2 is the cumulative addition / subtraction of partial products of 2 8th power term and 2 9th power term from step 026 to 031.

  In step 032, the operation of only shifting the contents of the accumulator 5 to the right by 2 bits is performed, and the effective digits are aligned. Finally, an arithmetic result of 16 bits in total is obtained with the 12 bits fractional part 4 bits with integer part sign.

  According to the present embodiment, the inner product operation is performed by accumulating the partial inner product for every two bits of the constant vector element. Therefore, the number of partial products to be accumulated can be reduced, and the control step can be reduced. The number of cycles can be further reduced. For example, when the third embodiment (FIG. 6) is compared with the present embodiment (FIG. 8), 41 steps are required in FIG. 6, whereas in FIG. 8, the calculation speed is improved by 32 steps and about 20%. Is made.

(Fifth embodiment)
Next, a fifth embodiment of the present invention will be described with reference to FIGS. In addition, the same code | symbol is attached | subjected to the same part as the 1st-4th embodiment mentioned above, and description is abbreviate | omitted. FIG. 9 is a configuration diagram of a computing unit portion of a microprocessor that executes the inner product computing method according to the fifth embodiment of the present invention. FIG. 10 shows a machine language instruction code format of the microprocessor shown in FIG. FIG. 11 is a part of a program list showing the inner product calculation operation of the microprocessor shown in FIG. FIG. 12 shows another part of the program list showing the inner product calculation operation of the microprocessor shown in FIG. FIG. 13 is a flowchart of the inner product calculation method operating in the microprocessor shown in FIG.

  This embodiment shows an inner product calculation method that can be executed by a program instruction such as a microprocessor. In particular, an inner product calculation method that can be implemented by a microprocessor that does not have a dedicated multiplication circuit and instruction or an inner product calculation dedicated circuit and instruction.

  The microprocessor 20 as the arithmetic unit shown in FIG. 3 includes an arithmetic logic unit (ALU) 22 as addition / subtraction means for performing logical product / logical sum / arithmetic addition / arithmetic subtraction, and an accumulator in which the arithmetic result of the ALU 22 is stored. 24, a register 26 as storage means connected to the accumulator 24 and the barrel shifter 28 via the bus 30, and a barrel shifter 28 as shift means for shifting the operand data sent from the register 26 to the ALU 22 by shifting leftward. I have.

  The ALU 22 is an arithmetic logic unit having a 16-bit word length, and the output of the barrel shifter 28 is connected to one input, and the operand data sent from the register 26 is shifted to the left and input to the ALU 22. The output of the accumulator 24 is connected to the other input, the output of the ALU 22 is connected to the accumulator 24, and the operation result of the ALU 22 is stored in the accumulator 24.

  The accumulator 24 has a 16-bit word length and is connected to the register 26 via the other input of the ALU 22 and the 8-bit width bus 30 so that the data accumulated in the accumulator 24 can be transferred to the register 26. It is.

  The register 26 includes, for example, 32 8-bit wide registers R0 to R31 as general-purpose registers.

  The barrel shifter 28 shifts the 8-bit data (operand data) stored in the register 26 by a shift amount specified by a machine language instruction code, which will be described later, and outputs the data to the ALU 22 as 16-bit data.

  As shown in FIG. 10, the machine language instruction code 37 includes information on the operation type C, the sign extension designation S, and the shift amount BSH. The operation type C includes addition, subtraction, logical product, and logical sum operations, and is distinguished by the value of C. The sign extension S includes zero extension and sign extension. In the case of zero extension, 0 is specified for S, and 1 is specified for S in the case of sign extension. The shift amount BSH can be specified from zero digits to 15 digits.

  FIG. 11 and FIG. 12 show a program list for performing an inner product calculation in the microprocessor 20 having the above-described configuration. Here, it is assumed that the input vector element is stored in a register labeled TmR0 (R0 of register 26) to TmR7 (R7 of register 26). The program lists shown in FIG. 11 and FIG. 12 are also used when obtaining Z1 of Equation 4 in the same manner as FIG. 2, FIG. 4, FIG. 6, and FIG.

Next, the instruction mnemonic will be described.
lda # 0
This instruction is a mnemonic for an instruction that loads the accumulator 24 with a zero value.
add TmR0: s0
This instruction is a mnemonic of an instruction that calls and adds the register value of the source operand “TmR0” to the value of the accumulator 24. “: S0” and an auxiliary code are added to the right of the source operand “TmR0”, but this is a left shift with a sign and bit extension of the number of bits following “s” and reading the register value. Means to perform an action. Similarly, “sub” is a subtraction instruction.

“Sta” is an instruction to write the contents of the accumulator 24 to the destination operand.
sta TmR12: z5
This is written with “: z5” and an auxiliary code added to the right side of the destination operand “TmR12”, which is shifted to the right by the number of bits following “z” to store the accumulator 24. The operation of transferring the contents to the register 26 is performed. “Lda” is an instruction for reading the immediate value or the register value of the source operand to the accumulator 24.

  In the program lists shown in FIGS. 11 and 12, a line with a semicolon added is a comment line, and the instruction on that line is not executed. In the figure, an instruction mnemonic is left as a comment for easy understanding. The instruction in the comment line represents the addition / subtraction of the partial products of the digits whose constant vector bit value is “0”, and as described in the first embodiment, addition / subtraction of these partial products is not executed.

  11 and 12, the numerical values and operations of the constant vector elements are the same as those in the first embodiment, but the general operation will be described with reference to the flowchart of FIG.

  First, the accumulator 24 is loaded with a zero value and reset (step S1, first line in FIG. 11), the partial product of the least significant digit of the constant vector element is obtained, the partial product is accumulated, and all the constant vector elements are accumulated. (Steps S2 to S4, for example, 8 steps below COEF_bit1 MUL / ADD in FIG. 11). That is, step S2 corresponds to the first step in the claims, and step S3 corresponds to the second step in the claims.

  Next, move to the next higher digit (step S5), find the partial product of the least significant digit of the constant vector element, accumulate the partial product, and repeat until the accumulation of all the constant vector elements is completed ( Steps S6 to S8, for example, 8 steps below COEF_bit2 MUL / ADD in FIG. This repetition is repeated until the most significant digit is completed, and when it is completed to the most significant digit, the process is terminated (step S11). That is, step S6 corresponds to the first step in the claims, and step S7 corresponds to the second step in the claims.

  When the accumulated result reaches the maximum digit of the accumulator 24, it is shifted to the right by 5 bits and rounded down (steps S9, S10, intermediate result / overflow (16 bits) avoidance part in FIG. 11). That is, step S10 corresponds to the third step in the claims. As with the first embodiment, the five bits to be discarded are bits equal to or less than the number obtained by subtracting the logarithm of the bit word length of the input vector element and the number of input vector elements from 2 as the bit word length of the adder / subtractor 4. It is calculated from the number of digits and determined in advance.

  In this embodiment, the calculation result is stored in the accumulator 24 and has a 16-bit width. However, labels of TmR12 (R12 of the register 26) and TmR13 (R13 of the register 26) are passed to the next stage program instruction. Are transferred separately to the lower and upper registers. In addition, the rounding-off operation by 5-bit right shift in the middle of the calculation is performed in the upper and lower order for the convenience of register width and instruction set.

  According to the present embodiment, in the microprocessor 20 having no dedicated multiplication circuit and instruction or inner product calculation dedicated circuit and instruction, the partial product of the same digit is obtained by using the addition / subtraction instruction in which the shift of the source operand is integrated. By accumulating in order from the lower order, it is possible to perform the inner product operation without lowering the carry from the lower digit accumulation, that is, ensuring the operation accuracy. In addition, since there is a step of once shifting and rounding the result in the middle of accumulation, a highly accurate inner product operation can be realized even with a microprocessor having a word length smaller than the maximum word length of multiplication.

(Sixth embodiment)
Next, a sixth embodiment of the present invention will be described with reference to FIG. In addition, the same code | symbol is attached | subjected to the same part as the 1st-5th embodiment mentioned above, and description is abbreviate | omitted. FIG. 14 is a program list showing the inner product calculation operation of the microprocessor according to the sixth embodiment of the present invention.

  This embodiment has the same configuration as that of the fifth embodiment, but adopts a second-order Booth algorithm as described in the second and fourth embodiments, and every 2 bits of the constant vector element, The partial product to be added or subtracted from the 3-bit pattern with the lower bits added, that is, the input vector element itself “M” or its double value “2M” is accumulated. That is, the first step selects either the input vector element itself or a value twice the input vector element to obtain a partial product, and the second step performs partial product accumulation every two bits. ing.

  FIG. 14 shows a program list of the operation of this embodiment. FIG. 14 also shows a case where Z1 of Equation 4 is obtained in the same manner as FIGS. 2, 4, 6, 8, 11, and 12. Since the calculation contents are the same as those in the second embodiment, description thereof will be omitted.

  According to the present embodiment, the inner product operation is performed by accumulating the partial inner product for every two bits of the constant vector element. Therefore, the number of partial products to be accumulated can be reduced, and the control step can be reduced. The number of cycles can be further reduced. For example, comparing the fifth embodiment (FIGS. 11 and 12) and the present embodiment (FIG. 14), FIG. 6 requires 48 steps, whereas FIG. 8 requires 38 steps and about 20% of computation. Speed improvements are made.

  The present invention is not limited to the above embodiment. That is, various modifications can be made without departing from the scope of the present invention.

1 inner product arithmetic unit 2 input element register (storage means)
3 Barrel shifter (shift means)
4 Adder / Subtracter (addition / subtraction means)
5 Accumulator 6 Shifter (Rounding means)
7 selector 8 control unit (calculation control means)
9 Adder / Subtracter (addition / subtraction means)
10 Shifter (first shift means)
11 Shifter (second shift means)
12 selector 13 adder / subtracter (addition / subtraction means)
14 Shifter (first shift means)
20 Microprocessor (computing device)
22 ALU (addition / subtraction means)
24 accumulator 26 register (storage means)
28 Barrel shifter (shifting means)

Japanese Patent Publication No. 5-26229 JP 2000-132539 A

Claims (8)

In an inner product arithmetic device for obtaining an inner product of an input vector composed of a plurality of input vector elements having a predetermined bit word length and a constant vector composed of a plurality of constant vector elements,
Storage means for storing the plurality of input vector elements;
Shift means for selecting the input vector element from the storage means and shifting the selected input vector to the left bit to obtain a partial product of the power vector of the constant vector element and the input vector element;
Adding / subtracting means configured to accumulate the partial product obtained by the shift means and configured with a bit number smaller than the multiplication precision required when the input vector element and the constant vector element are multiplied;
An accumulator for storing the accumulation result of the addition / subtraction means;
Rounding means for rounding off the operation result by truncating the result stored in the accumulator during accumulation by the addition / subtraction means by a bit shift of a predetermined number of digits;
The addition / subtraction means causes the accumulator to accumulate partial products of all input vector elements related to the same term of the least-significant power-of-two term of the constant vector element, and thereafter sequentially stores the higher 2 The accumulation of the partial product related to the power term is repeated until the most significant power term of 2 is stored, and stored in the accumulator in the middle of the summation by the rounding means before overflow of the addition / subtraction means occurs. Arithmetic control means that operates so that the lower digits of the result are truncated and set to the initial value of the subsequent accumulation;
An inner product arithmetic device comprising:   The arithmetic control means causes the shift means to obtain the partial product for every two bits of the input vector element based on a predetermined table, and causes the addition / subtraction means to accumulate the partial products. The inner product arithmetic device according to claim 1.   The rounding means truncates the result stored in the accumulator in the middle of accumulation by the addition / subtraction means. The inner product calculation device according to claim 1 or 2, wherein the inner product calculation device is predetermined as a number of bit digits equal to or less than a number obtained by subtracting a logarithm with 2 as a base. In an inner product arithmetic device for obtaining an inner product of an input vector composed of a plurality of input vector elements having a predetermined bit word length and a constant vector composed of a plurality of constant vector elements,
Storage means for storing the plurality of input vector elements;
The input vector element is selected from the storage means, a partial product of the power vector of the constant vector element and the selected input vector element is obtained and accumulated, and the input vector element and the constant vector are accumulated. Addition / subtraction means configured with a bit number smaller than the multiplication accuracy required when multiplying elements;
An accumulator for storing the accumulation result of the adding / subtracting means on its upper digit side;
The accumulator content is right-bit shifted in the lower digit direction to obtain the subsequent accumulated value, and the number of bit digits smaller than the multiplication accuracy required when the input vector element and the constant vector element are multiplied. Configured first shift means;
The addition / subtraction means accumulates the partial products of all input vector elements related to the same term of the power-of-two term of the same digit of the constant vector element, and stores it in the accumulator, and the first shift means Arithmetic control means for repeating the operation of right-bit shifting the accumulation result stored in the accumulator up to the most significant digit of the power vector of the constant vector element;
An inner product arithmetic device comprising: A second shift means for doubling the input vector element stored in the storage means;
The calculation control means selects either the input vector element stored in the storage means or the input vector element doubled by the second shift means based on a predetermined table and adds it to the addition / subtraction means. 5. The inner product operation device according to claim 4, wherein the first product is accumulated and the first shift means is shifted by 2 bits. Storage means for storing an input vector composed of a plurality of input vector elements having a predetermined bit word length, and a power of 2 of a constant vector composed of a plurality of constant vector elements by left-bit shifting the input vector Shift means for obtaining a partial product of a term and the input vector element, and multiplication required when the partial product obtained by the shift means is accumulated and the input vector element and the constant vector element are multiplied. Addition / subtraction means configured with a number of bit digits smaller than the precision and an accumulator for storing an accumulation result of the addition / subtraction means, using an instruction that can execute addition / subtraction and shift of operands integrally in a microprocessor In an inner product calculation method for obtaining an inner product of an input vector and the constant vector,
A first step in which the shift means selects the input vector element from the storage means to obtain the partial product;
A second step of causing the accumulator to perform accumulation of the partial products of all the input vector elements according to the same term of the least significant power-of-two term of the constant vector element, and to store in the accumulator;
A third step of truncating the lower digits of the result stored in the accumulator that is being stored in the accumulator before overflow of the addition / subtraction means occurs and setting the initial value for the subsequent accumulation; ,
With
The first step and the second step are sequentially repeated to accumulate the partial products for the higher power of 2 to the highest power of 2, and the first and second steps are repeated. An inner product calculation method, wherein the third step is performed at least once during the repetition of the step. In the first step, the partial product is obtained by selecting either the input vector element itself or a value twice the input vector element.
7. The inner product calculation method according to claim 6, wherein in the second step, the partial product is accumulated every two bits.   In the third step, the number of bit digits for truncating the result stored in the accumulator during accumulation by the adder / subtracter is calculated from the bitword length of the adder / subtractor and the bitword length of the input vector element and the input vector The inner product calculation method according to claim 6 or 7, wherein the inner product calculation method is predetermined as a number of bit digits equal to or less than a number obtained by subtracting a logarithm having 2 as the base of the number of elements.

Images