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/*

 * ====================================================

 * Copyright (C) 1998, 2002 by Red Hat Inc. All rights reserved.

 *

 * Permission to use, copy, modify, and distribute this

 * software is freely granted, provided that this notice

 * is preserved.

 * ====================================================

 */

#if !defined(_SOFT_FLOAT)

/*

Fast version of pow using Intel float instructions.

   double _f_pow (double x, double y);

Function calculates x to power of y.

The function optimizes the case where x is >0.0 and y is finite.

In such a case, there is no error checking or setting of errno.

All other cases defer to normal pow() function which will

set errno as normal.

*/

#include <math.h>

#include <ieeefp.h>

#include "f_math.h"

double _f_pow (double x, double y)

{

  /* following sequence handles the majority of cases for pow() */

  if (x > 0.0 && check_finite(y))

    {

      double result;

      /* calculate x ** y as 2 ** (y log2(x)).  On Intel, can only

         raise 2 to an integer or a small fraction, thus, we have

         to perform two steps 2**integer portion * 2**fraction. */

      asm ("fyl2x; fld %%st; frndint; fsub %%st,%%st(1);"\

           "fxch; fchs; f2xm1; fld1; faddp; fxch; fld1; fscale; fstp %%st(1);"\

           "fmulp" : "=t" (result) : "0" (x), "u" (y) : "st(1)" );

      return result;

    }

  else /* all other strange cases, defer to normal pow() */

    return pow (x,y);

}

#endif