Re: cmath and pow

[Chris Prince <prince at wcug dot wwu dot edu>]

On 1 Oct 1999, Gabriel Dos_Reis wrote:

> Then I'd like to see pow() prototype (in <math.h>)

  Sorry about that, the prototype is actually in __math.h and looks like
this...
__MATH_INLINE double pow (double __x, double __y);
__MATH_INLINE double
pow (double __x, double __y)
{
  register double __value, __exponent;
  long long int __p = (long long int) __y;
  if (__x == 0.0 && __y > 0.0)
    return 0.0;
  if (__y == (double) __p)
    {
      double __r = 1.0;
      if (__p == 0)
        return 1.0;
      if (__p < 0)
        {
          __p = -__p;
          __x = 1.0 / __x;

       }
      while (1)
        {
          if (__p & 1)
            __r *= __x;
          __p >>= 1;
          if (__p == 0)
            return __r;
          __x *= __x;
        }
      /* NOTREACHED */
    }
  __asm __volatile__
    ("fmul      %%st(1)         # y * log2(x)\n\t"
     "fstl      %%st(1)\n\t"
     "frndint                   # int(y * log2(x))\n\t"
     "fxch\n\t"
     "fsub      %%st(1)         # fract(y * log2(x))\n\t"
     "f2xm1                     # 2^(fract(y * log2(x))) - 1\n\t"
     : "=t" (__value), "=u" (__exponent) :  "0" (__log2 (__x)), "1" (__y));
  __value += 1.0;
  __asm __volatile__
    ("fscale"
     : "=t" (__value) : "0" (__value), "u" (__exponent));
  return __value;
}

__MATH_INLINE double floor (double __x);
__MATH_INLINE double
floor (double __x)
{
  register double __value;
  __volatile unsigned short int __cw, __cwtmp;
  __asm __volatile ("fnstcw %0" : "=m" (__cw));
  __cwtmp = (__cw & 0xf3ff) | 0x0400; /* rounding down */
  __asm __volatile ("fldcw %0" : : "m" (__cwtmp));
  __asm __volatile ("frndint" : "=t" (__value) : "0" (__x));
  __asm __volatile ("fldcw %0" : : "m" (__cw));
  return __value;
}


Chris :)
prince@wcug.wwu.edu
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