1 /* 2 * ==================================================== 3 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 4 * 5 * Developed at SunPro, a Sun Microsystems, Inc. business. 6 * Permission to use, copy, modify, and distribute this 7 * software is freely granted, provided that this notice 8 * is preserved. 9 * ==================================================== 10 */ 11 12 #include <sys/cdefs.h> 13 /* 14 * Float version of e_log10.c. See the latter for most comments. 15 */ 16 17 #include "math.h" 18 #include "math_private.h" 19 #include "k_logf.h" 20 21 static const float 22 two25 = 3.3554432000e+07, /* 0x4c000000 */ 23 ivln10hi = 4.3432617188e-01, /* 0x3ede6000 */ 24 ivln10lo = -3.1689971365e-05, /* 0xb804ead9 */ 25 log10_2hi = 3.0102920532e-01, /* 0x3e9a2080 */ 26 log10_2lo = 7.9034151668e-07; /* 0x355427db */ 27 28 static const float zero = 0.0; 29 static volatile float vzero = 0.0; 30 31 float 32 log10f(float x) 33 { 34 float f,hfsq,hi,lo,r,y; 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/vzero; /* 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 if (hx == 0x3f800000) 49 return zero; /* log(1) = +0 */ 50 k += (hx>>23)-127; 51 hx &= 0x007fffff; 52 i = (hx+(0x4afb0d))&0x800000; 53 SET_FLOAT_WORD(x,hx|(i^0x3f800000)); /* normalize x or x/2 */ 54 k += (i>>23); 55 y = (float)k; 56 f = x - (float)1.0; 57 hfsq = (float)0.5*f*f; 58 r = k_log1pf(f); 59 60 /* See e_log2f.c and e_log2.c for details. */ 61 if (sizeof(float_t) > sizeof(float)) 62 return (r - hfsq + f) * ((float_t)ivln10lo + ivln10hi) + 63 y * ((float_t)log10_2lo + log10_2hi); 64 hi = f - hfsq; 65 GET_FLOAT_WORD(hx,hi); 66 SET_FLOAT_WORD(hi,hx&0xfffff000); 67 lo = (f - hi) - hfsq + r; 68 return y*log10_2lo + (lo+hi)*ivln10lo + lo*ivln10hi + hi*ivln10hi + 69 y*log10_2hi; 70 } 71