reactos/lib/crtdll/math/pow.c

   1 /* Math functions for i387.
   2    Copyright (C) 1995, 1996, 1997 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by John C. Bowman <bowman@ipp-garching.mpg.de>, 1995.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Library General Public License as
   8    published by the Free Software Foundation; either version 2 of the
   9    License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Library General Public License for more details.
  15
  16    You should have received a copy of the GNU Library General Public
  17    License along with the GNU C Library; see the file COPYING.LIB.  If not,
  18    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  19    Boston, MA 02111-1307, USA.  */
  20
  21 double pow (double __x, double __y);
  22
  23 double __log2 (double __x);
  24
  25 double __log2 (double __x)
  26 {
  27   register double __value;
  28   __asm __volatile__
  29     ("fld1\n\t"
  30      "fxch\n\t"
  31      "fyl2x"
  32      : "=t" (__value) : "0" (__x));
  33
  34   return __value;
  35 }
  36
  37 double pow (double __x, double __y)
  38 {
  39   register double __value, __exponent;
  40   long __p = (long) __y;
  41
  42   if (__x == 0.0 && __y > 0.0)
  43     return 0.0;
  44   if (__y == (double) __p)
  45     {
  46       double __r = 1.0;
  47       if (__p == 0)
  48         return 1.0;
  49       if (__p < 0)
  50         {
  51           __p = -__p;
  52           __x = 1.0 / __x;
  53         }
  54       while (1)
  55         {
  56           if (__p & 1)
  57             __r *= __x;
  58           __p >>= 1;
  59           if (__p == 0)
  60             return __r;
  61           __x *= __x;
  62         }
  63       /* NOTREACHED */
  64     }
  65   __asm __volatile__
  66     ("fmul      %%st(1)         # y * log2(x)\n\t"
  67      "fst       %%st(1)\n\t"
  68      "frndint                   # int(y * log2(x))\n\t"
  69      "fxch\n\t"
  70      "fsub      %%st(1)         # fract(y * log2(x))\n\t"
  71      "f2xm1                     # 2^(fract(y * log2(x))) - 1\n\t"
  72      : "=t" (__value), "=u" (__exponent) :  "0" (__log2 (__x)), "1" (__y));
  73   __value += 1.0;
  74   __asm __volatile__
  75     ("fscale"
  76      : "=t" (__value) : "0" (__value), "u" (__exponent));
  77
  78   return __value;
  79 }
  80
  81 long double powl (long double __x,long double __y)
  82 {
  83         return pow(__x,__y/2)*pow(__x,__y/2);
  84 }
  85