Math circuit for estimating a transcendental function

摘要

A math circuit for computing an estimate of a transcendental function is described. A lookup table storage circuit has stored therein several groups of binary values, where each group of values represents a respective coefficient of a first polynomial that estimates the function to a high precision. A computing circuit uses a portion of a binary value, that is also taken from one of the groups of values, to evaluate a second polynomial that estimates the function to a low precision. Other embodiments are also described and claimed.

主权项

1. A circuit for computing an estimate of a transcendental function, comprising:
a lookup table storage circuit having stored therein a plurality of groups of values, each group of values representing a respective coefficient of a first polynomial that estimates the transcendental function to a first precision; and a first computing circuit coupled to the lookup table storage circuit to use portions of two groups of values representing two lowest-order coefficients of the first polynomial to evaluate a second polynomial that estimates the transcendental function to a second precision, wherein the second precision is lower than the first precision and the order of the second polynomial is lower than the order of the first polynomial, wherein the first computing circuit comprises:
an adjustment circuit to adjust the portion of the value representing the lowest-order coefficient that is taken from the lookup table storage circuit into an adjusted lowest-order coefficient of the second polynomial by adding an offset value, anda multiply add circuit to use the adjusted lowest-order coefficient and the portion of the value representing the first-order coefficient of the first polynomial to evaluate the second polynomial; wherein the circuit uses the lookup table storage circuit to evaluate both the first polynomial and the second polynomial.