Digital signal processor having instruction set with an exponential function using reduced look-up table

摘要

A digital signal processor is provided having an instruction set with an exponential function that uses a reduced look-up table. The disclosed digital signal processor evaluates an exponential function for an input value, x, by decomposing the input value, x, to an integer part, N, a first fractional part, q₁, larger than a specified value, x₀, and a second fractional part, q₂, smaller than the specified value, x₀; computing 2^q₂ using a polynomial approximation, such as a cubic approximation; obtaining 2^q₁ from a look-up table; and evaluating the exponential function for the input value, x, by multiplying 2^q₂, 2^q₁ and 2^N together. Look-up table entries have a fewer number of bits than a number of bits in the input value, x.