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 pow using Intel float instructions.
15
16 double _f_pow (double x, double y);
17
18 Function calculates x to power of y.
19 The function optimizes the case where x is >0.0 and y is finite.
20 In such a case, there is no error checking or setting of errno.
21 All other cases defer to normal pow() function which will
22 set errno as normal.
23 */
24
25 #include <math.h>
26 #include <ieeefp.h>
27 #include "f_math.h"
28
_f_pow(double x,double y)29 double _f_pow (double x, double y)
30 {
31 /* following sequence handles the majority of cases for pow() */
32 if (x > 0.0 && check_finite(y))
33 {
34 double result;
35 /* calculate x ** y as 2 ** (y log2(x)). On Intel, can only
36 raise 2 to an integer or a small fraction, thus, we have
37 to perform two steps 2**integer portion * 2**fraction. */
38 __asm__("fyl2x; fld %%st; frndint; fsub %%st,%%st(1);"\
39 "fxch; fchs; f2xm1; fld1; faddp; fxch; fld1; fscale; fstp %%st(1);"\
40 "fmulp" : "=t" (result) : "0" (x), "u" (y) : "st(1)" );
41 return result;
42 }
43 else /* all other strange cases, defer to normal pow() */
44 return pow (x,y);
45 }
46
47 #endif
48
