| The Android Open Source Project | a27d2ba | 2008-10-21 07:00:00 -0700 | [diff] [blame^] | 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 | #ifndef lint |
| 17 | static char rcsid[] = "$FreeBSD: src/lib/msun/src/e_log10f.c,v 1.8 2002/05/28 18:15:04 alfred Exp $"; |
| 18 | #endif |
| 19 | |
| 20 | #include "math.h" |
| 21 | #include "math_private.h" |
| 22 | |
| 23 | static const float |
| 24 | two25 = 3.3554432000e+07, /* 0x4c000000 */ |
| 25 | ivln10 = 4.3429449201e-01, /* 0x3ede5bd9 */ |
| 26 | log10_2hi = 3.0102920532e-01, /* 0x3e9a2080 */ |
| 27 | log10_2lo = 7.9034151668e-07; /* 0x355427db */ |
| 28 | |
| 29 | static const float zero = 0.0; |
| 30 | |
| 31 | float |
| 32 | __ieee754_log10f(float x) |
| 33 | { |
| 34 | float y,z; |
| 35 | int32_t i,k,hx; |
| 36 | |
| 37 | GET_FLOAT_WORD(hx,x); |
| 38 | |
| 39 | k=0; |
| 40 | if (hx < 0x00800000) { /* x < 2**-126 */ |
| 41 | if ((hx&0x7fffffff)==0) |
| 42 | return -two25/zero; /* log(+-0)=-inf */ |
| 43 | if (hx<0) return (x-x)/zero; /* log(-#) = NaN */ |
| 44 | k -= 25; x *= two25; /* subnormal number, scale up x */ |
| 45 | GET_FLOAT_WORD(hx,x); |
| 46 | } |
| 47 | if (hx >= 0x7f800000) return x+x; |
| 48 | k += (hx>>23)-127; |
| 49 | i = ((u_int32_t)k&0x80000000)>>31; |
| 50 | hx = (hx&0x007fffff)|((0x7f-i)<<23); |
| 51 | y = (float)(k+i); |
| 52 | SET_FLOAT_WORD(x,hx); |
| 53 | z = y*log10_2lo + ivln10*__ieee754_logf(x); |
| 54 | return z+y*log10_2hi; |
| 55 | } |