e_log10f.cpp (1978B)
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 //__FBSDID("$FreeBSD$"); 14 15 /* 16 * Float version of e_log10.c. See the latter for most comments. 17 */ 18 19 #include "math.h" 20 #include "math_private.h" 21 #include "k_logf.h" 22 23 static const float 24 two25 = 3.3554432000e+07, /* 0x4c000000 */ 25 ivln10hi = 4.3432617188e-01, /* 0x3ede6000 */ 26 ivln10lo = -3.1689971365e-05, /* 0xb804ead9 */ 27 log10_2hi = 3.0102920532e-01, /* 0x3e9a2080 */ 28 log10_2lo = 7.9034151668e-07; /* 0x355427db */ 29 30 static const float zero = 0.0; 31 static volatile float vzero = 0.0; 32 33 float 34 __ieee754_log10f(float x) 35 { 36 float f,hfsq,hi,lo,r,y; 37 int32_t i,k,hx; 38 39 GET_FLOAT_WORD(hx,x); 40 41 k=0; 42 if (hx < 0x00800000) { /* x < 2**-126 */ 43 if ((hx&0x7fffffff)==0) 44 return -two25/vzero; /* log(+-0)=-inf */ 45 if (hx<0) return (x-x)/zero; /* log(-#) = NaN */ 46 k -= 25; x *= two25; /* subnormal number, scale up x */ 47 GET_FLOAT_WORD(hx,x); 48 } 49 if (hx >= 0x7f800000) return x+x; 50 if (hx == 0x3f800000) 51 return zero; /* log(1) = +0 */ 52 k += (hx>>23)-127; 53 hx &= 0x007fffff; 54 i = (hx+(0x4afb0d))&0x800000; 55 SET_FLOAT_WORD(x,hx|(i^0x3f800000)); /* normalize x or x/2 */ 56 k += (i>>23); 57 y = (float)k; 58 f = x - (float)1.0; 59 hfsq = (float)0.5*f*f; 60 r = k_log1pf(f); 61 62 /* See e_log2f.c and e_log2.c for details. */ 63 if (sizeof(float_t) > sizeof(float)) 64 return (r - hfsq + f) * ((float_t)ivln10lo + ivln10hi) + 65 y * ((float_t)log10_2lo + log10_2hi); 66 hi = f - hfsq; 67 GET_FLOAT_WORD(hx,hi); 68 SET_FLOAT_WORD(hi,hx&0xfffff000); 69 lo = (f - hi) - hfsq + r; 70 return y*log10_2lo + (lo+hi)*ivln10lo + lo*ivln10hi + hi*ivln10hi + 71 y*log10_2hi; 72 }