Fast Multiple-Precision Evaluation of Elementary Functions

Let ƒ( x ) be one of the usual elementary functions (exp, log, artan, sin, cosh, etc.), and let M ( n ) be the number of single-precision operations required to multiply n -bit integers. It is shown that ƒ( x ) can be evaluated, with relative error Ο (2 - n ), in Ο ( M ( n )log ( n )) operations as n → ∞, for any floating-point number x (with an n -bit fraction) in a suitable finite interval. From the Schönhage-Strassen bound on M ( n ), it follows that an n -bit approximation to ƒ( x ) may be evaluated in Ο ( n log 2 ( n ) log log( n )) operations. Special cases include the evaluation of constants such as π, e , and e π . The algorithms depend on the theory of elliptic integrals, using the arithmetic-geometric mean iteration and ascending Landen transformations.