1*2fe8fb19SBen Gras /* e_log10f.c -- float version of e_log10.c.
2*2fe8fb19SBen Gras * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
3*2fe8fb19SBen Gras */
4*2fe8fb19SBen Gras
5*2fe8fb19SBen Gras /*
6*2fe8fb19SBen Gras * ====================================================
7*2fe8fb19SBen Gras * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
8*2fe8fb19SBen Gras *
9*2fe8fb19SBen Gras * Developed at SunPro, a Sun Microsystems, Inc. business.
10*2fe8fb19SBen Gras * Permission to use, copy, modify, and distribute this
11*2fe8fb19SBen Gras * software is freely granted, provided that this notice
12*2fe8fb19SBen Gras * is preserved.
13*2fe8fb19SBen Gras * ====================================================
14*2fe8fb19SBen Gras */
15*2fe8fb19SBen Gras
16*2fe8fb19SBen Gras #include <sys/cdefs.h>
17*2fe8fb19SBen Gras #if defined(LIBM_SCCS) && !defined(lint)
18*2fe8fb19SBen Gras __RCSID("$NetBSD: e_log10f.c,v 1.8 2002/05/26 22:01:51 wiz Exp $");
19*2fe8fb19SBen Gras #endif
20*2fe8fb19SBen Gras
21*2fe8fb19SBen Gras #include "math.h"
22*2fe8fb19SBen Gras #include "math_private.h"
23*2fe8fb19SBen Gras
24*2fe8fb19SBen Gras static const float
25*2fe8fb19SBen Gras two25 = 3.3554432000e+07, /* 0x4c000000 */
26*2fe8fb19SBen Gras ivln10 = 4.3429449201e-01, /* 0x3ede5bd9 */
27*2fe8fb19SBen Gras log10_2hi = 3.0102920532e-01, /* 0x3e9a2080 */
28*2fe8fb19SBen Gras log10_2lo = 7.9034151668e-07; /* 0x355427db */
29*2fe8fb19SBen Gras
30*2fe8fb19SBen Gras static const float zero = 0.0;
31*2fe8fb19SBen Gras
32*2fe8fb19SBen Gras float
__ieee754_log10f(float x)33*2fe8fb19SBen Gras __ieee754_log10f(float x)
34*2fe8fb19SBen Gras {
35*2fe8fb19SBen Gras float y,z;
36*2fe8fb19SBen Gras int32_t i,k,hx;
37*2fe8fb19SBen Gras
38*2fe8fb19SBen Gras GET_FLOAT_WORD(hx,x);
39*2fe8fb19SBen Gras
40*2fe8fb19SBen Gras k=0;
41*2fe8fb19SBen Gras if (hx < 0x00800000) { /* x < 2**-126 */
42*2fe8fb19SBen Gras if ((hx&0x7fffffff)==0)
43*2fe8fb19SBen Gras return -two25/zero; /* log(+-0)=-inf */
44*2fe8fb19SBen Gras if (hx<0) return (x-x)/zero; /* log(-#) = NaN */
45*2fe8fb19SBen Gras k -= 25; x *= two25; /* subnormal number, scale up x */
46*2fe8fb19SBen Gras GET_FLOAT_WORD(hx,x);
47*2fe8fb19SBen Gras }
48*2fe8fb19SBen Gras if (hx >= 0x7f800000) return x+x;
49*2fe8fb19SBen Gras k += (hx>>23)-127;
50*2fe8fb19SBen Gras i = ((u_int32_t)k&0x80000000)>>31;
51*2fe8fb19SBen Gras hx = (hx&0x007fffff)|((0x7f-i)<<23);
52*2fe8fb19SBen Gras y = (float)(k+i);
53*2fe8fb19SBen Gras SET_FLOAT_WORD(x,hx);
54*2fe8fb19SBen Gras z = y*log10_2lo + ivln10*__ieee754_logf(x);
55*2fe8fb19SBen Gras return z+y*log10_2hi;
56*2fe8fb19SBen Gras }
57