sysdeps/ieee754/flt-32/e_log10f.c

   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 __ieee754_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 (__builtin_expect((hx&0x7fffffff)==0, 0))
  38                 return -two25/(x-x);            /* log(+-0)=-inf */
  39             if (__builtin_expect(hx<0, 0))
  40                 return (x-x)/(x-x);     /* log(-#) = NaN */
  41             k -= 25; x *= two25; /* subnormal number, scale up x */
  42             GET_FLOAT_WORD(hx,x);
  43         }
  44         if (__builtin_expect(hx >= 0x7f800000, 0)) return x+x;
  45         k += (hx>>23)-127;
  46         i  = ((u_int32_t)k&0x80000000)>>31;
  47         hx = (hx&0x007fffff)|((0x7f-i)<<23);
  48         y  = (float)(k+i);
  49         SET_FLOAT_WORD(x,hx);
  50         z  = y*log10_2lo + ivln10*__ieee754_logf(x);
  51         return  z+y*log10_2hi;
  52 }
  53 strong_alias (__ieee754_log10f, __log10f_finite)