1. Circuitry for computing a first trigonometric function of an original input value, said circuitry comprising: circuitry for deriving an alternate input value from said original input value; circuitry for selecting a trigonometric input value from among candidate values including said original input value and said alternate input value, said circuitry for selecting selecting said alternate input value when said original input value is less than a threshold; circuitry for determining respective initial values of a plurality of respective trigonometric functions of said trigonometric input value; and circuitry for deriving, based at least in part on a trigonometric identity involving said original input value and said alternate input value, a final value of said first trigonometric function of said original input value from said respective initial values of said plurality of respective trigonometric functions of said trigonometric input value.