Arithmetic unit for approximating function
First Claim
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1. An arithmetic unit for approximating a function, comprising:
- a look-up table including a circuit configured to be connected to a register and output an initial value, an inclination of a straight line and at least one of relative correction values for the initial value and the inclination in response to an entry of a high-order bit string, an operand from the register being divided into the high-order bit string and a low-order bit string, a domain of the function of the operand being divided into a plurality of segments associated with the high-order bit string, the function being approximated by the straight line indicating a value equal to the initial value at a reference value in one of the segments;
an offset circuit configured to calculate an offset of the low-order bit string from the reference value;
a determination circuit configured to determine whether a correction of the straight line is necessary by using high-order bits in the low-order bit string;
a correction circuit configured to output the inclination obtained by adding an absolute correction value based on the relative correction values to at least one of the initial value and the inclination or by subtracting the absolute correction value from at least one of the initial value and the inclination, when the correction is necessary;
a multiplier configured to calculate a product of the inclination and the offset; and
an adder configured to calculate the sum of the initial value and the product and output the sum to the register,wherein the correction circuit comprises;
an adder-subtractor configured to output a corrected inclination obtained by adding the absolute correction value to the inclination or subtracting the absolute correction value from the inclination; and
a selector configured to select the corrected inclination when correction is necessary, whereby the size of the look-up table circuit is kept small.
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Abstract
A look-up table outputs an initial value, an inclination of a straight line and a correction value in response to an entry-of a high-order bit string of an operand. An offset circuit calculates an offset of the low-order bit string. A correction circuit outputs the initial value obtained by adding the correction value to at least one of the initial value and the inclination when the correction is necessary. A multiplier calculates a product of the inclination and the offset. An adder calculates the sum of the initial value and the product.
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Citations
15 Claims
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1. An arithmetic unit for approximating a function, comprising:
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a look-up table including a circuit configured to be connected to a register and output an initial value, an inclination of a straight line and at least one of relative correction values for the initial value and the inclination in response to an entry of a high-order bit string, an operand from the register being divided into the high-order bit string and a low-order bit string, a domain of the function of the operand being divided into a plurality of segments associated with the high-order bit string, the function being approximated by the straight line indicating a value equal to the initial value at a reference value in one of the segments; an offset circuit configured to calculate an offset of the low-order bit string from the reference value; a determination circuit configured to determine whether a correction of the straight line is necessary by using high-order bits in the low-order bit string; a correction circuit configured to output the inclination obtained by adding an absolute correction value based on the relative correction values to at least one of the initial value and the inclination or by subtracting the absolute correction value from at least one of the initial value and the inclination, when the correction is necessary; a multiplier configured to calculate a product of the inclination and the offset; and an adder configured to calculate the sum of the initial value and the product and output the sum to the register, wherein the correction circuit comprises; an adder-subtractor configured to output a corrected inclination obtained by adding the absolute correction value to the inclination or subtracting the absolute correction value from the inclination; and a selector configured to select the corrected inclination when correction is necessary, whereby the size of the look-up table circuit is kept small. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. An arithmetic unit for approximating a function, comprising:
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a look-up table including a circuit configured to be connected to a register and output an initial value, an inclination of a straight line and a relative correction value for the initial value in response to an entry of a high-order bit string, an operand from the register being divided into the high-order bit string and a low-order bit string, a domain of the function of the operand being divided into a plurality of segments associated with the high-order bit string, the function being approximated by the straight line indicating a value equal to the initial value at a reference value in one of the segments; an offset circuit configured to calculate an offset of the low-order bit string from the reference value; a determination circuit configured to determine whether a correction of the straight line is necessary by using the high-order bits in the low-order bit string; a correction circuit configured to output the inclination obtained by adding an absolute correction value based on the relative correction values to the initial value or by subtracting the absolute correction value from the initial value, when the correction is necessary; a multiplier configured to calculate a product of the inclination and the offset; and an adder configured to calculate the sum of the initial value and the product and output the sum to the register, wherein the absolute correction value is obtained by shifting the offset by the relative correction value as a shift amount, and wherein the correction circuit comprises; a shifter configured to generate the absolute correction value in conformity with the shift amount; and an adder-subtractor configured to output a corrected initial value obtained by adding or subtracting the absolute correction value to or from the initial value, whereby the size of the look-up table circuit is kept small. - View Dependent Claims (13, 14)
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15. An arithmetic unit for approximating a function, comprising:
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a look-up table including a circuit configured to be connected to a register and output an initial value, an inclination of a straight line and a correction value for the inclination in response to an entry of a high-order bit string, an operand from the register being divided into the high-order bit string and a low-order bit string, a domain of the function of the operand being divided into a plurality of segments associated with the high-order bit string, the function being approximated by the straight line indicating a value equal to the initial value at a reference value in one of the segments; an offset circuit configured to calculate an offset of the low-order bit string from the reference value; a determination circuit configured to determine whether a correction of the straight line is necessary by using high-order bits in the low-order bit string; a correction circuit configured to output the inclination obtained by adding the correction value to the inclination or by subtracting the correction value from the inclination, when the correction is necessary; a multiplier calculating a product of the inclination and the offset; and an adder calculating the sum of the initial value and the product and output the sum to the register, wherein the correction circuit comprises; an adder-subtractor configured to output a corrected inclination obtained by adding the correction value to the inclination or subtracting the correction value from the inclination; and a selector configured to select the corrected inclination when correction is necessary, whereby the size of the look-up table circuit is kept small.
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Specification