xref: /netbsd/lib/libm/src/e_log10f.c (revision 6550d01e)
1 /* e_log10f.c -- float version of e_log10.c.
2  * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
3  */
4 
5 /*
6  * ====================================================
7  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
8  *
9  * Developed at SunPro, a Sun Microsystems, Inc. business.
10  * Permission to use, copy, modify, and distribute this
11  * software is freely granted, provided that this notice
12  * is preserved.
13  * ====================================================
14  */
15 
16 #include <sys/cdefs.h>
17 #if defined(LIBM_SCCS) && !defined(lint)
18 __RCSID("$NetBSD: e_log10f.c,v 1.8 2002/05/26 22:01:51 wiz Exp $");
19 #endif
20 
21 #include "math.h"
22 #include "math_private.h"
23 
24 static const float
25 two25      =  3.3554432000e+07, /* 0x4c000000 */
26 ivln10     =  4.3429449201e-01, /* 0x3ede5bd9 */
27 log10_2hi  =  3.0102920532e-01, /* 0x3e9a2080 */
28 log10_2lo  =  7.9034151668e-07; /* 0x355427db */
29 
30 static const float zero   =  0.0;
31 
32 float
33 __ieee754_log10f(float x)
34 {
35 	float y,z;
36 	int32_t i,k,hx;
37 
38 	GET_FLOAT_WORD(hx,x);
39 
40         k=0;
41         if (hx < 0x00800000) {                  /* x < 2**-126  */
42             if ((hx&0x7fffffff)==0)
43                 return -two25/zero;             /* log(+-0)=-inf */
44             if (hx<0) return (x-x)/zero;        /* log(-#) = NaN */
45             k -= 25; x *= two25; /* subnormal number, scale up x */
46 	    GET_FLOAT_WORD(hx,x);
47         }
48 	if (hx >= 0x7f800000) return x+x;
49 	k += (hx>>23)-127;
50 	i  = ((u_int32_t)k&0x80000000)>>31;
51         hx = (hx&0x007fffff)|((0x7f-i)<<23);
52         y  = (float)(k+i);
53 	SET_FLOAT_WORD(x,hx);
54 	z  = y*log10_2lo + ivln10*__ieee754_logf(x);
55 	return  z+y*log10_2hi;
56 }
57