toolchain/gcc/newlib/libc/machine/i386/f_powf.c

   1 /*
   2  * ====================================================
   3  * Copyright (C) 1998, 2002 by Red Hat Inc. All rights reserved.
   4  *
   5  * Permission to use, copy, modify, and distribute this
   6  * software is freely granted, provided that this notice
   7  * is preserved.
   8  * ====================================================
   9  */
  10
  11 #if !defined(_SOFT_FLOAT)
  12
  13 /*
  14 Fast version of pow using Intel float instructions.
  15
  16    float _f_powf (float x, float y);
  17
  18 Function calculates x to power of y.
  19 The function optimizes the case where x is >0.0 and y is finite.
  20 In such a case, there is no error checking or setting of errno.
  21 All other cases defer to normal powf() function which will
  22 set errno as normal.
  23 */
  24
  25 #include <math.h>
  26 #include <ieeefp.h>
  27 #include "f_math.h"
  28
  29 float _f_powf (float x, float y)
  30 {
  31   /* following sequence handles the majority of cases for pow() */
  32   if (x > 0.0 && check_finitef(y))
  33     {
  34       float result;
  35       /* calculate x ** y as 2 ** (y log2(x)).  On Intel, can only
  36          raise 2 to an integer or a small fraction, thus, we have
  37          to perform two steps 2**integer portion * 2**fraction. */
  38       asm ("flds 8(%%ebp); fyl2x; fld %%st; frndint; fsub %%st,%%st(1);" \
  39            "fxch; fchs; f2xm1; fld1; faddp; fxch; fld1; fscale; fstp %%st(1);"\
  40            "fmulp" : "=t" (result) : "0" (y));
  41       return result;
  42     }
  43   else /* all other strange cases, defer to normal pow() */
  44     return powf (x,y);
  45 }
  46
  47 #endif