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 #include "math.h" 17 #include "math_private.h" 18 19 static const float 20 two25 = 3.3554432000e+07, /* 0x4c000000 */ 21 ivln10 = 4.3429449201e-01, /* 0x3ede5bd9 */ 22 log10_2hi = 3.0102920532e-01, /* 0x3e9a2080 */ 23 log10_2lo = 7.9034151668e-07; /* 0x355427db */ 24 25 static const float zero = 0.0; 26 27 float 28 log10f(float x) 29 { 30 float y,z; 31 int32_t i,k,hx; 32 33 GET_FLOAT_WORD(hx,x); 34 35 k=0; 36 if (hx < 0x00800000) { /* x < 2**-126 */ 37 if ((hx&0x7fffffff)==0) 38 return -two25/zero; /* log(+-0)=-inf */ 39 if (hx<0) return (x-x)/zero; /* log(-#) = NaN */ 40 k -= 25; x *= two25; /* subnormal number, scale up x */ 41 GET_FLOAT_WORD(hx,x); 42 } 43 if (hx >= 0x7f800000) return x+x; 44 k += (hx>>23)-127; 45 i = ((u_int32_t)k&0x80000000)>>31; 46 hx = (hx&0x007fffff)|((0x7f-i)<<23); 47 y = (float)(k+i); 48 SET_FLOAT_WORD(x,hx); 49 z = y*log10_2lo + ivln10*logf(x); 50 return z+y*log10_2hi; 51 } 52