Hi there, some time ago I asked Intel whether the implementations of fma(), fmaf() and fmal() they ship with the Intel C/C++ compiler do conform to the C99 standard. Here is their answer, for future reference: ANSWER: ___________________________________________________ Yes, fma(), fmaf() and fmal(), defined in libimf.a/.so, are conforming to C99. FMA ( Defined on page 233 of Intel® C++ Compiler for Linux* Systems user's Guide) Description: The fma functions return (x*y)+z. Calling interface: double fma(double x, double y, long double z); long double fmal(long double x, long double y, long double z); float fmaf(float x, float y, long double z); Quote from ISO/IEC 9899:1999 (C99) standard: 7.12.13.1 The fma functions Synopsis #include <math.h> double fma(double x, double y, double z); float fmaf(float x, float y, float z); long double fmal(long double x, long double y, long double z); Description The fma functions compute (x* y) + z, rounded as one ternary operation: they compute the value (as if) to infinite precision and round once to the result format, according to the rounding mode characterized by the value of FLT_ROUNDS. Returns The fma functions return (x*y) + z, rounded as one ternary operation. ------------ Some related macros: The macro FP_FAST_FMA, is optionally defined. If defined, it indicates that the fma function generally executes about as fast as, or faster than, a multiply and an add of double operands.193) The macros FP_FAST_FMAF FP_FAST_FMAL are, respectively, float and long double analogs of FP_FAST_FMA. Please read in /opt/intel_cc_80/include/mathimf.h. -- Prof. Roberto Bagnara Computer Science Group Department of Mathematics, University of Parma, Italy http://www.cs.unipr.it/~bagnara/ mailto:bagnara@cs.unipr.it