libgcc-math/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 #if defined(LIBM_SCCS) && !defined(lint)
  17 static char rcsid[] = "$NetBSD: e_log10f.c,v 1.5 1995/05/10 20:45:53 jtc Exp $";
  18 #endif
  19
  20 #include "math_private.h"
  21
  22 #ifdef __STDC__
  23 static const float
  24 #else
  25 static float
  26 #endif
  27 two25      =  3.3554432000e+07, /* 0x4c000000 */
  28 ivln10     =  4.3429449201e-01, /* 0x3ede5bd9 */
  29 log10_2hi  =  3.0102920532e-01, /* 0x3e9a2080 */
  30 log10_2lo  =  7.9034151668e-07; /* 0x355427db */
  31
  32 #ifdef __STDC__
  33 static const float zero   =  0.0;
  34 #else
  35 static float zero   =  0.0;
  36 #endif
  37
  38 #ifdef __STDC__
  39         float __ieee754_log10f(float x)
  40 #else
  41         float __ieee754_log10f(x)
  42         float x;
  43 #endif
  44 {
  45         float y,z;
  46         int32_t i,k,hx;
  47
  48         GET_FLOAT_WORD(hx,x);
  49
  50         k=0;
  51         if (hx < 0x00800000) {                  /* x < 2**-126  */
  52             if ((hx&0x7fffffff)==0)
  53                 return -two25/(x-x);            /* log(+-0)=-inf */
  54             if (hx<0) return (x-x)/(x-x);       /* log(-#) = NaN */
  55             k -= 25; x *= two25; /* subnormal number, scale up x */
  56             GET_FLOAT_WORD(hx,x);
  57         }
  58         if (hx >= 0x7f800000) return x+x;
  59         k += (hx>>23)-127;
  60         i  = ((uint32_t)k&0x80000000)>>31;
  61         hx = (hx&0x007fffff)|((0x7f-i)<<23);
  62         y  = (float)(k+i);
  63         SET_FLOAT_WORD(x,hx);
  64         z  = y*log10_2lo + ivln10*__ieee754_logf(x);
  65         return  z+y*log10_2hi;
  66 }