JPH05100826A - Reciprocal arithmetic unit - Google Patents

Abstract

PURPOSE:To provide a high speed reciprocal arithmetic unit. CONSTITUTION:When the mantissa part of a calculated number is inputted, a conversion table storage part 11 stores a conversion table outputting 1/N of the reciprocal of inputted value. A subtraction part 12 outputs a value obtained by subtracting the value inputted from one when the index part of the calculated number is inputted. A constant generation part 13 outputs a constant 1/N when the mantissa part of the calculated number is positive, and constant -1/N when it is negative. A subtraction part 14 outputs a value obtained by subtracting a value inputted from 2. An operation result selection part 15 sets a floating point number where the output of the constant generation part 13 is set to be the mantissa part and the output of the subtraction part 14 as output as first input, and sets the floating point number where the output of the conversion table storage part 11 as the mantissa part and the output of the subtraction part 12 as the index part as second input so as to input them. When the absolute value of the mantissa part of the calculated number is equal to 1/N, first input is selected. When it is not equal, second input is selected so as to be outputted as an operation result.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reciprocal arithmetic unit, and more particularly to a reciprocal arithmetic unit for a normalized floating point number based on a power of two.

[0002]

2. Description of the Related Art A mantissa whose base is a power N of 2 is m.
(However, 1 / N ≦ | m | <1), and the reciprocal of the normalized floating-point number whose exponent part is n can be expressed as follows.

[0003]

[Equation 1] Therefore, for the reciprocal of the operand of the normalized floating point number, the reciprocal of the mantissa of the operand is the mantissa of the operation result, and the sign of the exponent of the operand is inverted to the exponent of the operation result. Is required by However, since the reciprocal number thus obtained does not become a normalized state, it is necessary to perform a normalization process.

FIG. 5 is an explanatory diagram showing a conventional example of a reciprocal arithmetic unit.

The conversion table storage unit 50 stores in advance a conversion table from the mantissa part m of the operand to the mantissa part 1 / m of the reciprocal, and stores the operand to be input from the input mantissa signal line 501. The reciprocal corresponding to the value of the mantissa is calculated by the mantissa signal line 503.
Output to. The code conversion unit 51 is an input exponent signal line 50.
A value obtained by inverting the sign of the exponent of the operand to be input from 2 is output to the exponent signal line 504. Input mantissa signal line 50
1 and the input exponent part signal line 502 are obtained by separating the mantissa part and exponent part from the input signal line 500 for inputting the operand.

The normalization processing control unit 52 uses the mantissa signal line 5
Information necessary for the normalization processing is obtained from the value input from 03 and output to the normalization control signal line 505. The mantissa part normalization processing unit 53 performs a normalization process for performing digit alignment of the amount indicated by the normalization control signal line 505 on the mantissa part of the reciprocal input from the mantissa part signal line 503, and the normalized reciprocal number is calculated. The mantissa value is output to the mantissa signal line 506. The exponent part normalization processing unit 54 performs a normalization process of adding the amount indicated by the normalization control signal line 505 to the exponent part of the reciprocal input from the exponent part signal line 504, and the normalized reciprocal exponent. The value of the part is output to the exponent part signal line 507.

Mantissa signal line 506 and exponent signal line 5
The normalized reciprocal of the operand is output to the output signal line 508 which is the sum of 07.

[0008]

The above-mentioned conventional reciprocal arithmetic unit obtains the information necessary for the normalization process from the result of indexing the conversion table storage unit by the process of the mantissa part and calculates the mantissa part and the exponent part. Since the normalization processing is performed, there are drawbacks that the signal propagation delay time is long and the operation speed is slow.

An object of the present invention is to provide a high speed reciprocal arithmetic unit.

[0010]

A reciprocal arithmetic unit according to the present invention uses a power N of 2 as a radix and has a mantissa part m of 1 / N≤ |
In a reciprocal arithmetic unit for a normalized floating-point number with m | <1, a storage unit that stores a conversion table that outputs 1 / N of the reciprocal of the input value when the mantissa part of the operand is input, and the operand When the exponent part of is input, the first arithmetic means for outputting a value obtained by subtracting the input value from 1 and a constant 1 / N when the mantissa part of the operand is positive, and a constant -1 / when the mantissa is negative Constant generating means for outputting N, and second arithmetic means for outputting a value obtained by subtracting the input value from 2 when the exponent part of the operand is input,
The output of the constant generating means is the mantissa part, the output of the second computing means is the exponent part, the floating point number is the first input, the output of the storage means is the mantissa part, and the output of the first computing means Input a floating-point number with exponent as the second input, and select the first input when the absolute value of the mantissa part of the operand is equal to 1 / N, and select the second input when not equal. And selecting means for outputting as a calculation result.

The reciprocal arithmetic unit of the present invention is a reciprocal arithmetic unit for a normalized floating-point number whose base number is a power N of 2 and whose mantissa part m is 1 / N≤ | m | <1. A storage unit that stores a conversion table that outputs 1 / N of the reciprocal of the input value when the mantissa of the number is input, and a constant 1 / N when the mantissa of the operand is positive and a constant when the mantissa is negative. A first constant generating means for outputting −1 / N, and a second constant generating means for outputting a constant 2 when the absolute value of the mantissa part of the operand is equal to 1 / N, and a constant 1 otherwise. Means for selecting the output of the first constant generating means when the absolute value of the mantissa part of the operand is equal to 1 / N, and selecting and outputting the output of the storing means when the absolute values are not equal; And an arithmetic means for subtracting the exponent part of the operand from the output of the constant generating means and outputting the result. The output of the 4-option means the mantissa, and outputs a floating point number as the operation result to exponent output of the arithmetic unit.

Furthermore, the reciprocal arithmetic unit of the present invention is a reciprocal arithmetic unit for a normalized floating point number, in which the mantissa part m is 1 / N≤ | m | <1 as a base number and the mantissa m is 1 A conversion table that outputs 1 / N ² of the reciprocal of the input value when it is equal to 1 / N of the reciprocal of the input value when the mantissa part of the number is input, and 1 / N ² of the reciprocal of the input value when not equal 1 when the storage means for storing and the exponent part of the operand are input
The first arithmetic means for outputting a value obtained by subtracting the input value from the second arithmetic means, and the second arithmetic means for outputting a value obtained by subtracting the input value from 2 when the exponent part of the operand is input; And a selecting means for selecting and outputting the output of the second arithmetic means when the mantissa is equal to 1 / N, and the output of the first arithmetic means when the mantissa is not equal to the mantissa. And a floating point number whose output is the exponent part is output as a calculation result.

The reciprocal arithmetic unit of the present invention is a reciprocal arithmetic unit for a normalized floating point number having a mantissa m as 1 / N≤ | m | <1 as a radix, and the operand to be operated is N. When you input the mantissa part of the number, the absolute value of the input value is 1 / N
Storage means for storing a conversion table for outputting 1 / N ² of the reciprocal of the input value when they are equal to, and 1 / N of the reciprocal of the input value when not equal, and the mantissa part of the operand is 1 / N. A constant generating means for outputting a constant 2 when equal to N, and a constant 1 when not equal, and an arithmetic means for subtracting the exponent part of the operand from the output of the constant generating means and outputting the result,
It is characterized in that a floating point number whose output is the mantissa part and whose output is the exponent part is output as the operation result.

[0014]

Operation: The mantissa is m (where 1 / N≤ | m | <1),
The reciprocal of a normalized floating point number whose exponent part is a power of N of 2 and whose base is N can be expressed as follows.

[0015]

[Equation 2] From this equation, the normalized reciprocal can be obtained by the following method according to the value of the mantissa part m of the operand. (1) When 1 / N <| m | <1, the mantissa part of the reciprocal is 1 / m to the reciprocal 1 / m of the mantissa part m of the operand.
It is calculated by multiplying by N. The exponent part of the reciprocal is calculated by subtracting the exponent part n of the operand from 1. The mantissa part 1 / (mN) of the reciprocal obtained in this way is

[0016]

[Equation 3] In order to satisfy, the obtained reciprocal is a normalized one. (2) In the case of | m | = 1 / N, the mantissa part of the reciprocal is 1 / m to the reciprocal 1 / m of the mantissa part m of the operand.
It is calculated by multiplying by N ² . The exponent part of the reciprocal is calculated by subtracting the exponent part n of the operand from 2. The mantissa part 1 / (mN ² ) of the reciprocal thus obtained is

[0017]

[Equation 4] In order to satisfy, the obtained reciprocal is a normalized one.

Regarding both of the above (1) and (2),
The normalized calculation result is directly obtained, and it is not necessary to provide a normalizing means after the calculation.

[0019]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 1 is an explanatory view showing a first embodiment of the present invention.

The conversion table storage unit 11 stores in advance a conversion table for converting the mantissa part m of the operand to 1 / (mN), and the mantissa part of the operand input from the input mantissa signal line 101. The value of 1 / N of the reciprocal of is output to the mantissa signal line 103. The subtraction unit 12 outputs a value obtained by subtracting the exponent part n of the operand to be input from the input exponent part signal line 102 from 1, to the exponent part signal line 104. The input mantissa signal line 101 and the input exponent signal line 102 are obtained by separating the mantissa part and the exponent part from the input signal line 100 for inputting the operand. The constant generator 13 uses the input mantissa signal line 101.
If the mantissa part of the operand to be input from is positive, then a constant 1 / N
Is output to the mantissa signal line 105 having a constant −1 / N when it is negative. The constants 1 / N and -1 / N are respectively m
= When the 1 / N and -1 / N corresponds to 1 / (mN ²⁾ of the. The subtraction unit 14 uses the input exponent signal line 1
A value obtained by subtracting the exponent part n of the operand to be input from 02 from 2 is output to the exponent part signal line 106. The floating point number signal line 107 includes a mantissa part signal line 103 and an exponent part signal line 10.
It is a combination of four. Floating point signal line 108
Is a combination of the mantissa part signal line 105 and the exponent part signal line 106.

The operation result selection unit 15 inputs the floating point number signal line 108 when the absolute value of the mantissa part m of the input mantissa signal line 101 is equal to 1 / N, and the floating point number signal when it is not equal. The input from line 107 is selected and this value is output on output signal line 110. The value of the output signal line 110 is a normalized floating point number that is the reciprocal of the operand to be input to the input signal line 100.

FIG. 2 is an explanatory view showing the second embodiment of the present invention.

The conversion table storage unit 21 stores in advance a conversion table for converting the mantissa part m of the operand to 1 / (mN), and the mantissa part of the operand to be input from the input mantissa signal line 201. The value of 1 / N of the reciprocal of is output to the mantissa signal line 204. The constant generator 22 calculates the constant 1 / N when the mantissa of the operand to be input from the input mantissa signal line 201 is positive,
When it is negative, it is output to the mantissa signal line 205 having a constant −1 / N. The constants 1 / N and -1 / N are respectively m = 1.
It corresponds to 1 / (mN ² ) for / N and -1 / N. The mantissa part selection unit 24 uses the input mantissa signal line 2
When the absolute value of the mantissa part m of 01 is equal to 1 / N, the input from the mantissa signal line 205 is selected, and when the absolute value is not equal, the input from the mantissa signal line 204 is selected and this value is set to the mantissa signal line 207. Output to.

The constant generating section 23 is provided with the input mantissa signal line 20.
Constant 2 when the absolute value of the mantissa part m of 1 is equal to 1 / N
When they are not equal, the constant 1 is output to the constant signal line 206. The subtraction unit 25 subtracts the value input from the input command unit signal line 202 from the value input from the constant signal line 206, and outputs the calculation result to the exponent signal line 208.

The input mantissa signal line 201 and the input exponent signal line 202 are obtained by separating the mantissa part and exponent part from the input signal line 200 for inputting the operand. The output signal line 209 is a combination of the mantissa part signal line 207 and the exponent part signal line 208.
The reciprocal of the operand input to 00 is output as a normalized floating point number.

FIG. 3 is an explanatory diagram showing a third embodiment of the present invention.

When the mantissa part m of the operand is input to the conversion table storage unit 30 in advance, the absolute value of the mantissa part m becomes 1 / N.
A conversion table that outputs 1 / N ² of the reciprocal of m when it is not equal, and 1 / N of the reciprocal of m when not equal, and stores the mantissa of the operand to be input from the input mantissa signal line 301. The value corresponding to the copy is output to the mantissa signal line 303.

The subtractor 32 outputs a value obtained by subtracting the exponent part n of the operand to be input from the input exponent part signal line 302 from 1, to the exponent part signal line 305. The subtractor 33 outputs a value obtained by subtracting the exponent part n of the operand to be input from the input exponent part signal line 302 from 2, to the exponent part signal line 306. The input mantissa part signal line 301 and the input exponent part signal line 302 are obtained by separating the mantissa part and exponent part from the input signal line 300 for inputting the operand. The exponent part selection unit 34
When the absolute value of the mantissa part m of the input mantissa signal line 301 is equal to 1 / N, the input from the exponent part signal line 306 is selected, and when it is not equal, the input from the exponent part signal line 305 is selected and this value is selected. Output to the exponent part signal line 307. Output signal line 30
Reference numeral 8 is a combination of the mantissa part signal line 303 and the exponent part signal line 307, and outputs the reciprocal of the operand to be input to the input signal line 300 as a normalized floating point number.

FIG. 4 is an explanatory view showing the fourth embodiment of the present invention.

When the mantissa part m of the operand is input to the conversion table storage unit 40 in advance, the absolute value of the mantissa part m becomes 1 / N.
A conversion table that outputs 1 / N ² of the reciprocal of m when it is not equal, and 1 / N of the reciprocal of m when it is not equal, and stores the mantissa of the operand to be input from the input mantissa signal line 401. The value corresponding to the copy is output to the mantissa signal line 403.
The constant generator 41 calculates the mantissa part m of the input mantissa signal line 401.
When the absolute value of is equal to 1 / N, the constant 2 is output to the constant signal line 404. Subtraction unit 4
2 subtracts the value input from the input command section signal line 402 from the value input from the constant signal line 404, and outputs the calculation result to the exponent section signal line 405.

The input mantissa part signal line 401 and the input exponent part signal line 402 are obtained by separating the mantissa part and exponent part from the input signal line 400 for inputting the operand. The output signal line 406 is a combination of the mantissa part signal line 403 and the exponent part signal line 405.
The reciprocal of the operand input to 00 is output as a normalized floating point number.

[0033]

As described above, according to the present invention, since the normalized operation result is directly obtained and it is not necessary to provide the normalizing means after the operation, the circuit configuration is simple and the signal propagation delay time related to the operation is reduced. It is possible to reduce the calculation speed and increase the calculation speed.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a second embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a third embodiment of the present invention.

FIG. 4 is an explanatory diagram showing a fourth embodiment of the present invention.

FIG. 5 is an explanatory diagram showing a conventional example of a reciprocal arithmetic unit.

[Explanation of symbols]

 11 conversion table storage unit 12 subtraction unit 13 constant generation unit 14 subtraction unit 15 calculation result selection unit 100 input signal line 101 input mantissa signal line 102 input exponent signal line 103 mantissa signal line 104 exponent signal line 105 mantissa signal Line 106 Exponent signal line 107 Floating-point signal line 108 Floating-point signal line 110 Output signal line 21 Conversion table storage unit 22 Constant generation unit 23 Constant generation unit 24 Mantissa selection unit 25 Subtraction unit 200 Input signal line 201 Input mantissa signal Line 202 Input exponent signal line 204 Mantissa signal line 205 Mantissa signal line 206 Constant signal line 207 Mantissa signal line 208 Exponent signal line 209 Output signal line 30 Conversion table storage unit 32 Subtraction unit 33 Subtraction unit 34 Exponent selection Part 300 Input signal line 301 Input mantissa signal line 302 Input exponent part Signal line 303 Mantissa part Signal line 305 Exponent part signal line 306 Exponent part signal line 307 Exponent part signal line 308 Output signal line 40 Conversion table storage part 41 Constant generation part 42 Subtraction part 400 Input signal line 401 Input significand part signal line 402 Input exponent part signal line 403 Mantissa signal line 404 Constant signal line 405 Exponent signal line 406 Output signal line

Claims (4)

[Claims] 1. A reciprocal arithmetic unit for a normalized floating-point number in which a mantissa part m is 1 / N ≦ | m | <1 with a power of 2 as a radix, and is input when a mantissa part of an operand is input. 1 / the reciprocal of the value
Storage means for storing a conversion table for outputting N; first arithmetic means for outputting a value obtained by subtracting the input value from 1 when the exponent part of the operand is input; and the mantissa part of the operand is positive. A constant generating unit that outputs a constant 1 / N when the value is negative, and a constant -1 / N when the value is negative, and a second operation that outputs a value obtained by subtracting the input value from 2 when the exponent part of the operand is input. Means, and the output of the constant generating means as the mantissa part, the output of the second calculating means as the exponent part as a first input, the output of the storage means as the mantissa part, and the first operation A floating-point number whose exponent is the output of the means is input as the second input, and the first input is input when the absolute value of the mantissa part of the operand is equal to 1 / N, and the second input when not equal. A reciprocal arithmetic unit, comprising: selecting means for selecting an input and outputting as an arithmetic result. . 2. A reciprocal arithmetic unit for a normalized floating-point number in which a mantissa m is 1 / N ≦ | m | <1 and a mantissa of a operand is input when the mantissa of the operand is input. 1 / the reciprocal of the value
Storage means for storing a conversion table for outputting N; and a first constant generation means for outputting a constant 1 / N when the mantissa of the operand is positive and a constant -1 / N when the mantissa is negative. Second constant generating means for outputting a constant 2 when the absolute value of the mantissa part of the operand is equal to 1 / N, and a constant 1 when the absolute value of the mantissa part of the operand is not equal to 1 / N. First when equal to N
Selection means for selecting and outputting the output of the storage means when the outputs of the constant generating means are not equal, and an operation for subtracting the exponent part of the operand from the output of the second constant generating means and outputting the result. Means for outputting a floating-point number whose output is the mantissa part and whose output is the exponent part, as an operation result. 3. A reciprocal arithmetic unit for a normalized floating-point number, wherein a mantissa m is 1 / N ≦ | m | <1, and a mantissa of the operand is input when the mantissa of the operand is input. 1 / the reciprocal of the value
A storage means for storing a conversion table that outputs 1 / N ² of the reciprocal of the input value when it is equal to N, and 1 / N ² of the reciprocal of the input value when not equal, and an exponent part of the operand. Then, a first arithmetic means for outputting a value obtained by subtracting the input value from 1 and a second arithmetic means for outputting a value obtained by subtracting the input value from 2 when the exponent part of the operand is input, The output of the second arithmetic means when the mantissa part of the number is equal to 1 / N, and the selector means for selecting and outputting the output of the first arithmetic means when they are not equal, A reciprocal arithmetic unit, which outputs a floating point number having a mantissa part and an output of the selecting means being an exponent part as an arithmetic result. 4. A reciprocal arithmetic unit for a normalized floating-point number, wherein a mantissa m is 1 / N ≦ | m | <1 and a mantissa of the operand is input when the mantissa of the operand is input. The absolute value of the specified value is 1
/ N equals 1 / N ² of the reciprocal of the input value when not equal, and 1 / N of the reciprocal of the input value when not equal, and a storage means for storing a conversion table and a mantissa of the operand. A constant generating means for outputting a constant 2 when equal to 1 / N and a constant 1 when not equal, and an operating means for subtracting the exponent part of the operand from the output of the constant generating means and outputting the result. A reciprocal arithmetic unit which outputs a floating point number having an output of the storage unit as a mantissa and an output of the arithmetic unit as an exponent as an arithmetic result.