/*
* ====================================================
* 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.
float _f_powf (float x, float 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 powf() function which will
set errno as normal.
*/
#include <math.h>
#include <ieeefp.h>
#include "f_math.h"
float _f_powf (float x, float y)
{
/* following sequence handles the majority of cases for pow() */
if (x > 0.0 && check_finitef(y))
{
float 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 powf (x,y);
}
#endif