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 #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.h"
  21 #include "math_private.h"
  22
  23 #ifdef __STDC__
  24 static const float
  25 #else
  26 static float
  27 #endif
  28 two25      =  3.3554432000e+07, /* 0x4c000000 */
  29 ivln10     =  4.3429449201e-01, /* 0x3ede5bd9 */
  30 log10_2hi  =  3.0102920532e-01, /* 0x3e9a2080 */
  31 log10_2lo  =  7.9034151668e-07; /* 0x355427db */
  32
  33 #ifdef __STDC__
  34 static const float zero   =  0.0;
  35 #else
  36 static float zero   =  0.0;
  37 #endif
  38
  39 #ifdef __STDC__
  40         float __ieee754_log10f(float x)
  41 #else
  42         float __ieee754_log10f(x)
  43         float x;
  44 #endif
  45 {
  46         float y,z;
  47         int32_t i,k,hx;
  48
  49         GET_FLOAT_WORD(hx,x);
  50
  51         k=0;
  52         if (hx < 0x00800000) {                  /* x < 2**-126  */
  53             if ((hx&0x7fffffff)==0)
  54                 return -two25/(x-x);            /* log(+-0)=-inf */
  55             if (hx<0) return (x-x)/(x-x);       /* log(-#) = NaN */
  56             k -= 25; x *= two25; /* subnormal number, scale up x */
  57             GET_FLOAT_WORD(hx,x);
  58         }
  59         if (hx >= 0x7f800000) return x+x;
  60         k += (hx>>23)-127;
  61         i  = ((u_int32_t)k&0x80000000)>>31;
  62         hx = (hx&0x007fffff)|((0x7f-i)<<23);
  63         y  = (float)(k+i);
  64         SET_FLOAT_WORD(x,hx);
  65         z  = y*log10_2lo + ivln10*__ieee754_logf(x);
  66         return  z+y*log10_2hi;
  67 }