JP3272033B2 - Shifter circuit with sticking function - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shifter circuit having a sticking function which is used in a device (particularly, a digital signal processor) which executes an operation with a fixed-point value.

[0002]

2. Description of the Related Art In recent years, with the development of digital signal processing technology, digital signal processors (hereinafter referred to as DSPs) for executing arithmetic processing with fixed-point numerical values have been frequently used. Since the DSP processes the signal as discrete numerical values, complicated calculations can be easily realized.

[0003] The DSP includes a floating-point arithmetic DSP that performs internal numerical representation in two parts, a mantissa part and an exponent part.
And a fixed-point arithmetic DSP that performs internal numerical representation only with a mantissa. Here, the floating-point arithmetic DSP
Compared to a fixed-point arithmetic DSP, the range of representable numerical values is wider and the performance is higher, but on the other hand, it is large, expensive, and consumes large power. For this reason, in fields used in large quantities, it is common to use fixed-point arithmetic DSPs, especially for mobile phones where size and power consumption are a problem. ing.

However, in the fixed-point arithmetic DSP, a value that should be expressed by a mantissa part and an exponent part is represented only by a mantissa part. In this case, it is necessary to align the decimal point of the numerical value, and a shifter circuit is incorporated for aligning the decimal point of the numerical value in this calculation.

For example, when the decimal point position of the numerical value A is at the fifth bit from the most significant bit and the decimal point position of the numerical value B is at the seventh bit from the most significant bit, the shifter circuit Shifts A two bits to the right, and then performs addition processing with B.

As described above, when the input data bit width and the output data bit width of the shifter circuit are equal, overflow detection and pasting can be performed by comparing the most significant code bit of the input data with the most significant code bit of the output data. Easy. The overflow detecting operation and the sticking operation in the DSP are described in detail in the following documents. Reference: ADSP-2100 User's Manual analog devices

[0007]

By the way, in the fixed-point operation type DSP, the position of the decimal point is determined for each variable to be used. A method of selecting only a necessary portion from a large bit width by a shifter circuit is adopted.

[0008] A specific example will be described. Now, assuming that a 16-bit numerical value 0000 1010 1111 1010: 2810 (decimal notation) is input data of the shifter circuit, the shifter circuit selects the 8th bit after the fifth bit counting from the most significant bit of this input data. think of.

If the pasting is not performed, the output data becomes 1010 1111: -81 (decimal notation), and positive / negative inversion occurs in addition to a numerical error.

In the same processing, if the pasting is performed, the output data becomes 0111 1111: 127 (decimal notation), which is a number close to the original numerical value '175'.
Inconvenience such as reversal of positive / negative does not occur.

That is, in the case of a process of selecting only a necessary portion from a large bit width, if the pasting process is not properly performed, a positive / negative reversal occurs. As a result, a large error may occur. For this reason, it is important that the shifter circuit of the fixed-point arithmetic DSP has the attaching function. However, in the case of selecting only a necessary part from a large bit width, since the input data bit width of the shifter circuit is larger than the output data bit width, it is difficult to detect and paste output data overflow. If the processing is to be realized by hardware, the configuration of the shifter circuit becomes complicated, and there is a concern that inconveniences such as an increase in cost and an increase in the size of the circuit due to a large addition of hardware may occur.

Therefore, in the case of a conventional shifter circuit built in a fixed-point arithmetic DSP, the above-mentioned attaching function has been obtained by software. However, when the pasting function is supplemented by software, there is a problem that the processing speed is sacrificed.

[0013] The present invention has been made in view of the above circumstances, the processing can be speeded up by realizing the pasting processing by hardware, and the circuit configuration for executing the pasting processing is simple. It is another object of the present invention to provide a shifter circuit with a sticking function that can prevent an increase in hardware due to an increase in the amount of hardware and is suitable for being incorporated in a fixed-point arithmetic DSP or the like.

[0014]

According to the present invention, there is provided a shifter circuit with an attaching function according to the present invention, which shifts a bit sequence of input data based on a designated shift amount, and also generates a bit sequence indicating input data. An overflow detection circuit that outputs a bit string indicating a bit position at which an overflow occurs, and a first selection circuit that selects data at a bit position corresponding to the shift amount of the shifter circuit from the bit string output by the overflow detection circuit And a stitch used for stitching based on the input data.
Bit string is dynamically generated, and the selection of the first selection circuit is performed.
Depending on the selection result, the bit string output by the shifter circuit
Or a second selection circuit for selecting and outputting one of the attached bit strings .

The overflow detection circuit includes:
An exclusive OR circuit for detecting a bit inversion position on the bit string indicating the input data, and an OR circuit for transmitting the bit inversion detected by the exclusive OR circuit to the lower bit side.

[0016]

In the shifter circuit with the pasting function according to the present invention, since the pasting process is realized by hardware such as an overflow detection circuit, a first selection circuit, an AND circuit, and a second selection circuit, the processing is speeded up. be able to.

In addition, the amount of hardware that must be added to the shifter circuit, which is a basic circuit, to obtain the overflow detection circuit, the first selection circuit, the AND circuit, the second selection circuit, etc. An exclusive OR circuit, a logical OR circuit, an input selector having the same number of inputs as the bit width of the output data, a two-input selector, or the like may be used for one bit width of the data, and a circuit configuration for realizing the pasting process is required. To provide a shifter circuit with a sticking function that is simple and requires a very small amount of hardware, can prevent an increase in the amount of hardware, and can be prevented from increasing in size. Becomes possible.

Further, since the overflow detection circuit and the second selection circuit can be arranged in an orderly and regular circuit configuration as shown in FIGS. 2 and 3, it is easy to implement an LSI. It can be expected that compactness suitable for incorporating a fixed-point arithmetic DSP is further promoted.

[0019]

FIG. 1 is a block diagram of an embodiment of a shifter circuit with a sticking function according to the present invention. The shifter circuit with a sticking function according to this embodiment includes a data input terminal 1 for receiving data to be shifted, and a data input terminal 1 for receiving data input to the data input terminal 1 and detecting from which bit an overflow occurs. An overflow detection circuit 2; a shift amount input terminal 3 for designating a shift amount; and shift processing based on a shift amount specified from the shift amount input terminal 3 by receiving data input to the data input terminal 1. A shifter circuit 4, a first selection circuit 5 for selecting and outputting 1-bit information from the output of the overflow detection circuit 2, and a pasting instruction signal input unit 6 for determining whether to use the pasting function. ,
An AND circuit 7 for performing an AND operation on the signal of the pasting instruction signal input unit 6 and the output signal of the first selection circuit 5, and either a shifter value or a pasting value according to the output of the AND circuit 7. It comprises a second selection circuit 8 for selecting and outputting, and an output terminal 9 for sending out the data selected by the second selection circuit 8 to another circuit.

As shown in FIG. 2, the overflow detecting circuit 2 is an input unit 2 for extracting data of each bit from n-bit input data from the data input terminal 1.
0, an exclusive OR circuit 21 which receives two-bit data adjacent to each bit data extracted by the input unit 20 and detects a bit inversion position on a bit string indicating the input data; An OR circuit 22 for transmitting the bit inversion detected by the exclusive OR circuit 21 to the lower bits, and an output unit 24 for outputting the outputs of these OR circuits 22 as a bit string indicating the bit position at which overflow occurs. The data of the output unit 24 is output to the first selection circuit 5. In the bit string output from the overflow detection circuit 2 to the output unit 24, the value of the bit position at which an overflow occurs is “1”.

The shifter circuit 4 is a general circuit that shifts input data according to a designated shift amount. The conventional shifter circuit that obtains the pasting function by software is hardware-based.
, A data input terminal 1 and a shift amount input terminal 3.

The first selection circuit 5 receives the output of the overflow detection circuit 2 and the shift amount designated by the shift amount input terminal 3 as inputs and outputs the output data of the output section 24 of the overflow detection circuit 2. , And selectively outputs 1-bit information (ie, a bit value indicating whether or not overflow has occurred) corresponding to the designated shift amount, and has the same circuit configuration as one bit of the shifter circuit 4 (ie, The input selector is equal to the bit width of the output data.

The pasting instruction signal input section 6 is an input section for a signal indicating whether or not to use the pasting function. If the input signal is "1", it means "use the pasting function". If 0 ', "do not use the paste function"
Means that.

As shown in FIG. 3, the second selection circuit 8 outputs the output data of the shifter circuit 4 (ie, the shifter value).
, A second input unit 82 to which the most significant bit (ie, a pasted value) of the data input to the data input terminal 1 is input, and a third input unit 82 to receive the output of the AND circuit 7. An input unit 83 and either an input signal to the first input unit 81 or an input signal to the second input unit 82 using the input to the third input unit 83 (ie, the output of the AND circuit 7) as a control signal. Input selector (ie, 2 input selector) for selecting and outputting
(in1 selector) 84 and an output unit 85 for sending the output signal of the two-input selector 84 to the output terminal 9.

If the output of the AND circuit 7 is "1", the two-input selector 84 converts the signal input to the second input section 82 (ie, the value of the most significant bit) into an AND circuit. If the output of 7 is '0', the signal input to the first input section 81 (that is, the shifter value output from the shifter circuit 4) is output. The input signal to the second input unit 82 is supplied to an inverter 86 for the second and subsequent two-input selectors 84.
Is inverted.

In the above embodiment, a series of operations in the case where the overflow is detected and the pasting is performed will be described.
This will be described with reference to FIG.

First, when data is input to the data input terminal 1, the overflow detection circuit 2 calculates from which position the shifter circuit 4 selects data to cause an overflow. In the case of the circuit of FIG. 2, a bit string in which the bit position where overflow occurs is “1” is output. Then, from the output of each bit by the overflow detection circuit 2, the data at the bit position corresponding to the designated shift amount is selected by the first selection circuit 5 and output to the AND circuit 7. When the output from the first selection circuit 5 is 1, it means that an overflow occurs.

On the other hand, in the shifter circuit 4, as in the prior art,
The shift processing is performed on the input data to the data input terminal 1, and the processed shift value is output to the second selection circuit 8.

The AND circuit 7 outputs to the second selection circuit 8 a signal corresponding to the output of the first selection circuit 5 and the input signal of the sticking instruction signal input section 6. The output signal of the AND circuit 7 is output when the output of the first selection circuit 5 is "1" and the signal of the sticking instruction signal input unit 6 is "1" indicating sticking (that is, overflow is detected). Is set to “1” only when the pasting process is performed and the pasting process is instructed).

The second selection circuit 8 uses the output of the AND circuit 7 as a control signal to select either the shifter value output by the shifter circuit 4 or the paste value from the input data and outputs the selected signal to the output terminal 9. . The output of the AND circuit 7 is "1"
In the case of (2), the second selection circuit 8 selects the pasted value.

As described in detail above, in the shifter circuit with a sticking function according to one embodiment of the present invention, the overflow detection circuit 2, the first selection circuit 5, the logical product circuit 7, the second selection circuit 8, etc. Since the pasting processing is realized by hardware, the processing can be speeded up.

In addition, the overflow detection circuit 2,
The amount of hardware that must be added to the shifter circuit 4 in order to obtain circuits such as the first selection circuit 5, the AND circuit 7, and the second selection circuit 8 is exclusive for each bit width of output data. A logical OR circuit, a logical OR circuit, an input selector having the same number of inputs as the bit width of the output data, a two-input selector, etc. are required, and the circuit configuration for realizing the pasting process is simple and the necessary hardware amount It is possible to provide a shifter circuit with a sticking function suitable for being built in a fixed-point operation type DSP or the like, because the number of hardware components is extremely small, and an increase in the amount of hardware can be prevented.

As shown in FIGS. 2 and 3, since the overflow detection circuit 2 and the second selection circuit 8 have an orderly and regular circuit configuration, it is easy to implement LSI. Accordingly, it is expected that compactness suitable for incorporating a fixed-point arithmetic DSP can be promoted.

[0034]

As is apparent from the above description, in the shifter circuit with a pasting function according to the present invention, pasting is performed by hardware such as an overflow detection circuit, a first selection circuit, an AND circuit, and a second selection circuit. To realize the processing,
Processing can be sped up.

In addition, the amount of hardware that must be added to the shifter circuit, which is the basic circuit, to obtain the overflow detection circuit, the first selection circuit, the AND circuit, the second selection circuit, etc. An exclusive OR circuit, a logical OR circuit, an input selector having the same number of inputs as the bit width of the output data, a two-input selector, or the like may be used for one bit width of the data, and a circuit configuration for realizing the pasting process is required. To provide a shifter circuit with a sticking function that is simple and requires a very small amount of hardware, can prevent an increase in the amount of hardware, and can be prevented from increasing in size. Becomes possible.

Further, since the overflow detection circuit and the second selection circuit can be arranged in an orderly and regular circuit configuration as shown in FIGS. 2 and 3, it is easy to implement an LSI. It can be expected that compactness suitable for incorporating a fixed-point arithmetic DSP is further promoted.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of a shifter circuit with a pasting function according to the present invention.

FIG. 2 is a configuration diagram of an overflow detection circuit according to one embodiment of the present invention.

FIG. 3 is a configuration diagram of a second selection circuit in one embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Data input terminal 2 Overflow detection circuit 3 Shift amount input terminal 4 Shifter circuit 5 First selection circuit 6 Pasting instruction signal input section 7 AND circuit 8 Second selection circuit 9 Output terminal 20 Input section 21 Exclusive OR circuit Reference Signs List 22 OR circuit 24 Output section 81 First input section 82 Second input section 83 Third input section 84 2-input selector 85 Output section 86 Inverter

Continuation of the front page (56) References JP-A-4-76621 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G06F 5/01 G06F 7/00 G06F 7/38

Claims (1)

(57) [Claims] A shift circuit that shifts a bit string of input data based on a designated shift amount; an exclusive OR circuit that detects a bit inversion position on the bit string indicating the input data; An overflow circuit for transmitting a bit inversion detected by the exclusive OR circuit to the lower bit side, and outputting a bit string indicating a bit position at which an overflow occurs; and an output of the overflow detection circuit. A first selection circuit for selecting data at a bit position corresponding to the shift amount of the shifter circuit from a bit sequence to be executed, and a pasting unit used for pasting based on the input data
A bit string is dynamically generated, and a selection result of the first selection circuit is generated.
Depending on the result, the bit string output by the shifter circuit or
And a second selection circuit for selecting and outputting one of the pasted bit strings .