1*05a0b428SJohn Marino /* e_log10f.c -- float version of e_log10.c.
2*05a0b428SJohn Marino * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
3*05a0b428SJohn Marino */
4*05a0b428SJohn Marino
5*05a0b428SJohn Marino /*
6*05a0b428SJohn Marino * ====================================================
7*05a0b428SJohn Marino * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
8*05a0b428SJohn Marino *
9*05a0b428SJohn Marino * Developed at SunPro, a Sun Microsystems, Inc. business.
10*05a0b428SJohn Marino * Permission to use, copy, modify, and distribute this
11*05a0b428SJohn Marino * software is freely granted, provided that this notice
12*05a0b428SJohn Marino * is preserved.
13*05a0b428SJohn Marino * ====================================================
14*05a0b428SJohn Marino */
15*05a0b428SJohn Marino
16*05a0b428SJohn Marino #include "math.h"
17*05a0b428SJohn Marino #include "math_private.h"
18*05a0b428SJohn Marino
19*05a0b428SJohn Marino static const float
20*05a0b428SJohn Marino two25 = 3.3554432000e+07, /* 0x4c000000 */
21*05a0b428SJohn Marino ivln10 = 4.3429449201e-01, /* 0x3ede5bd9 */
22*05a0b428SJohn Marino log10_2hi = 3.0102920532e-01, /* 0x3e9a2080 */
23*05a0b428SJohn Marino log10_2lo = 7.9034151668e-07; /* 0x355427db */
24*05a0b428SJohn Marino
25*05a0b428SJohn Marino static const float zero = 0.0;
26*05a0b428SJohn Marino
27*05a0b428SJohn Marino float
log10f(float x)28*05a0b428SJohn Marino log10f(float x)
29*05a0b428SJohn Marino {
30*05a0b428SJohn Marino float y,z;
31*05a0b428SJohn Marino int32_t i,k,hx;
32*05a0b428SJohn Marino
33*05a0b428SJohn Marino GET_FLOAT_WORD(hx,x);
34*05a0b428SJohn Marino
35*05a0b428SJohn Marino k=0;
36*05a0b428SJohn Marino if (hx < 0x00800000) { /* x < 2**-126 */
37*05a0b428SJohn Marino if ((hx&0x7fffffff)==0)
38*05a0b428SJohn Marino return -two25/zero; /* log(+-0)=-inf */
39*05a0b428SJohn Marino if (hx<0) return (x-x)/zero; /* log(-#) = NaN */
40*05a0b428SJohn Marino k -= 25; x *= two25; /* subnormal number, scale up x */
41*05a0b428SJohn Marino GET_FLOAT_WORD(hx,x);
42*05a0b428SJohn Marino }
43*05a0b428SJohn Marino if (hx >= 0x7f800000) return x+x;
44*05a0b428SJohn Marino k += (hx>>23)-127;
45*05a0b428SJohn Marino i = ((u_int32_t)k&0x80000000)>>31;
46*05a0b428SJohn Marino hx = (hx&0x007fffff)|((0x7f-i)<<23);
47*05a0b428SJohn Marino y = (float)(k+i);
48*05a0b428SJohn Marino SET_FLOAT_WORD(x,hx);
49*05a0b428SJohn Marino z = y*log10_2lo + ivln10*logf(x);
50*05a0b428SJohn Marino return z+y*log10_2hi;
51*05a0b428SJohn Marino }
52