newlib/libm/common/s_fma.c

   1 /*
   2 FUNCTION
   3 <<fma>>, <<fmaf>>---floating multiply add
   4 INDEX
   5         fma
   6 INDEX
   7         fmaf
   8
   9 SYNOPSIS
  10         #include <math.h>
  11         double fma(double <[x]>, double <[y]>, double <[z]>);
  12         float fmaf(float <[x]>, float <[y]>, float <[z]>);
  13
  14 DESCRIPTION
  15 The <<fma>> functions compute (<[x]> * <[y]>) + <[z]>, rounded as one ternary
  16 operation:  they compute the value (as if) to infinite precision and round once
  17 to the result format, according to the rounding mode characterized by the value
  18 of FLT_ROUNDS.  That is, they are supposed to do this:  see below.
  19
  20 RETURNS
  21 The <<fma>> functions return (<[x]> * <[y]>) + <[z]>, rounded as one ternary
  22 operation.
  23
  24 BUGS
  25 This implementation does not provide the function that it should, purely
  26 returning "(<[x]> * <[y]>) + <[z]>;" with no attempt at all to provide the
  27 simulated infinite precision intermediates which are required.  DO NOT USE THEM.
  28
  29 If double has enough more precision than float, then <<fmaf>> should provide
  30 the expected numeric results, as it does use double for the calculation.  But
  31 since this is not the case for all platforms, this manual cannot determine
  32 if it is so for your case.
  33
  34 PORTABILITY
  35 ANSI C, POSIX.
  36
  37 */
  38
  39 #include "fdlibm.h"
  40
  41 #if !HAVE_FAST_FMA
  42
  43 #ifndef _DOUBLE_IS_32BITS
  44
  45 #ifdef __STDC__
  46         double fma(double x, double y, double z)
  47 #else
  48         double fma(x,y)
  49         double x;
  50         double y;
  51         double z;
  52 #endif
  53 {
  54   /* Implementation defined. */
  55   return (x * y) + z;
  56 }
  57
  58 #endif /* _DOUBLE_IS_32BITS */
  59
  60 #endif /* !HAVE_FAST_FMA */