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[/] [openrisc/] [tags/] [gnu-src/] [newlib-1.18.0/] [newlib-1.18.0-or32-1.0rc2/] [newlib/] [libc/] [machine/] [i386/] [f_pow.c] - Rev 520
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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 ("fldl 8(%%ebp); fyl2x; fld %%st; frndint; fsub %%st,%%st(1);" \ "fxch; fchs; f2xm1; fld1; faddp; fxch; fld1; fscale; fstp %%st(1);"\ "fmulp" : "=t" (result) : "0" (y)); return result; } else /* all other strange cases, defer to normal pow() */ return pow (x,y); } #endif