sdk/lib/crt/math/i386/exp.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 Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the 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    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, write to the Free
  18    Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  19    Boston, MA 02110-1301, USA.
  20 */
  21
  22 #include <math.h>
  23
  24 double exp (double __x);
  25
  26 double exp (double __x)
  27 {
  28 #ifdef __GNUC__
  29   register double __value, __exponent;
  30   __asm __volatile__
  31     ("fldl2e                    # e^x = 2^(x * log2(e))\n\t"
  32      "fmul      %%st(1)         # x * log2(e)\n\t"
  33      "fst       %%st(1)\n\t"
  34      "frndint                   # int(x * log2(e))\n\t"
  35      "fxch\n\t"
  36      "fsub      %%st(1)         # fract(x * log2(e))\n\t"
  37      "f2xm1                     # 2^(fract(x * log2(e))) - 1\n\t"
  38      : "=t" (__value), "=u" (__exponent) : "0" (__x));
  39   __value += 1.0;
  40   __asm __volatile__
  41     ("fscale"
  42      : "=t" (__value) : "0" (__value), "u" (__exponent));
  43
  44   return __value;
  45 #else
  46   register double __val;
  47   __asm
  48   {
  49     fld1                        // store 1.0 for later use
  50     fld __x
  51     fldl2e                      // e^x = 2^(x * log2(e))
  52     fmul    st,st(1)            // x * log2(e)
  53     fld     st(0)
  54     frndint                     // int(x * log2(e))
  55     fsub    st,st(1)            // fract(x * log2(e))
  56     fxch
  57     f2xm1                       // 2^(fract(x * log2(e))) - 1
  58     fadd    st,st(3)            // + 1.0
  59     fscale
  60     fstp __val
  61   }
  62   return __val;
  63 #endif /*__GNUC__*/
  64 }