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 #include <fix-int-fp-convert-zero.h>
  19
  20 static const float
  21 two25      =  3.3554432000e+07, /* 0x4c000000 */
  22 ivln10     =  4.3429449201e-01, /* 0x3ede5bd9 */
  23 log10_2hi  =  3.0102920532e-01, /* 0x3e9a2080 */
  24 log10_2lo  =  7.9034151668e-07; /* 0x355427db */
  25
  26 float
  27 __ieee754_log10f(float x)
  28 {
  29         float y,z;
  30         int32_t i,k,hx;
  31
  32         GET_FLOAT_WORD(hx,x);
  33
  34         k=0;
  35         if (hx < 0x00800000) {                  /* x < 2**-126  */
  36             if (__builtin_expect((hx&0x7fffffff)==0, 0))
  37               return -two25/__fabsf (x);        /* log(+-0)=-inf  */
  38             if (__builtin_expect(hx<0, 0))
  39                 return (x-x)/(x-x);     /* log(-#) = NaN */
  40             k -= 25; x *= two25; /* subnormal number, scale up x */
  41             GET_FLOAT_WORD(hx,x);
  42         }
  43         if (__builtin_expect(hx >= 0x7f800000, 0)) 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         if (FIX_INT_FP_CONVERT_ZERO && y == 0.0f)
  49           y = 0.0f;
  50         SET_FLOAT_WORD(x,hx);
  51         z  = y*log10_2lo + ivln10*__ieee754_logf(x);
  52         return  z+y*log10_2hi;
  53 }
  54 strong_alias (__ieee754_log10f, __log10f_finite)