toolchain/gcc/newlib/libc/machine/i386/f_exp.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 exp using Intel float instructions.
  15
  16    double _f_exp (double x);
  17
  18 Function computes e ** x.  The following special cases exist:
  19    1. if x is 0.0 ==> return 1.0
  20    2. if x is infinity ==> return infinity
  21    3. if x is -infinity ==> return 0.0
  22    4. if x is NaN ==> return x
  23 There is no error checking or setting of errno.
  24 */
  25
  26
  27 #include <math.h>
  28 #include <ieeefp.h>
  29 #include "f_math.h"
  30
  31 double _f_exp (double x)
  32 {
  33    if (check_finite(x))
  34      {
  35        double result;
  36        asm ("fldl2e; fmulp; fld %%st; frndint; fsub %%st,%%st(1); fxch;" \
  37           "fchs; f2xm1; fld1; faddp; fxch; fld1; fscale; fstp %%st(1); fmulp" :
  38           "=t"(result) : "0"(x));
  39        return result;
  40      }
  41    else if (x == -infinity())
  42      return 0.0;
  43
  44    return x;
  45 }
  46
  47 #endif