toolchain/gcc/newlib/libm/math/ef_log10.c

   1 /* ef_log10.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 "fdlibm.h"
  17
  18 #ifdef __STDC__
  19 static const float
  20 #else
  21 static float
  22 #endif
  23 two25      =  3.3554432000e+07, /* 0x4c000000 */
  24 ivln10     =  4.3429449201e-01, /* 0x3ede5bd9 */
  25 log10_2hi  =  3.0102920532e-01, /* 0x3e9a2080 */
  26 log10_2lo  =  7.9034151668e-07; /* 0x355427db */
  27
  28 #ifdef __STDC__
  29 static const float zero   =  0.0;
  30 #else
  31 static float zero   =  0.0;
  32 #endif
  33
  34 #ifdef __STDC__
  35         float __ieee754_log10f(float x)
  36 #else
  37         float __ieee754_log10f(x)
  38         float x;
  39 #endif
  40 {
  41         float y,z;
  42         __int32_t i,k,hx;
  43
  44         GET_FLOAT_WORD(hx,x);
  45
  46         k=0;
  47         if (FLT_UWORD_IS_ZERO(hx&0x7fffffff))
  48             return -two25/zero;             /* log(+-0)=-inf */
  49         if (hx<0) return (x-x)/zero;        /* log(-#) = NaN */
  50         if (!FLT_UWORD_IS_FINITE(hx)) return x+x;
  51         if (FLT_UWORD_IS_SUBNORMAL(hx)) {
  52             k -= 25; x *= two25; /* subnormal number, scale up x */
  53             GET_FLOAT_WORD(hx,x);
  54         }
  55         k += (hx>>23)-127;
  56         i  = ((__uint32_t)k&0x80000000)>>31;
  57         hx = (hx&0x007fffff)|((0x7f-i)<<23);
  58         y  = (float)(k+i);
  59         SET_FLOAT_WORD(x,hx);
  60         z  = y*log10_2lo + ivln10*__ieee754_logf(x);
  61         return  z+y*log10_2hi;
  62 }