compiler/stdc/math/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 #ifndef lint
  17 static char rcsid[] = "$FreeBSD: src/lib/msun/src/e_log10f.c,v 1.13 2011/10/16 05:36:23 das Exp $";
  18 #endif
  19
  20 /*
  21  * Float version of e_log10.c.  See the latter for most comments.
  22  */
  23
  24 #include "math.h"
  25 #include "math_private.h"
  26 #include "k_logf.h"
  27
  28 static const float
  29 two25      =  3.3554432000e+07, /* 0x4c000000 */
  30 ivln10hi   =  4.3432617188e-01, /* 0x3ede6000 */
  31 ivln10lo   = -3.1689971365e-05, /* 0xb804ead9 */
  32 log10_2hi  =  3.0102920532e-01, /* 0x3e9a2080 */
  33 log10_2lo  =  7.9034151668e-07; /* 0x355427db */
  34
  35 static const float zero   =  0.0;
  36 static const volatile float vzero __attribute__ ((__section__(".rodata"))) = 0.0;
  37
  38 float
  39 __ieee754_log10f(float x)
  40 {
  41         float f,hfsq,hi,lo,r,y;
  42         int32_t i,k,hx;
  43
  44         GET_FLOAT_WORD(hx,x);
  45
  46         k=0;
  47         if (hx < 0x00800000) {                  /* x < 2**-126  */
  48             if ((hx&0x7fffffff)==0)
  49                 return -two25/vzero;            /* log(+-0)=-inf */
  50             if (hx<0) return (x-x)/zero;        /* log(-#) = NaN */
  51             k -= 25; x *= two25; /* subnormal number, scale up x */
  52             GET_FLOAT_WORD(hx,x);
  53         }
  54         if (hx >= 0x7f800000) return x+x;
  55         if (hx == 0x3f800000)
  56             return zero;                        /* log(1) = +0 */
  57         k += (hx>>23)-127;
  58         hx &= 0x007fffff;
  59         i = (hx+(0x4afb0d))&0x800000;
  60         SET_FLOAT_WORD(x,hx|(i^0x3f800000));    /* normalize x or x/2 */
  61         k += (i>>23);
  62         y = (float)k;
  63         f = x - (float)1.0;
  64         hfsq = (float)0.5*f*f;
  65         r = k_log1pf(f);
  66
  67         /* See e_log2f.c and e_log2.c for details. */
  68         if (sizeof(float_t) > sizeof(float))
  69                 return (r - hfsq + f) * ((float_t)ivln10lo + ivln10hi) +
  70                     y * ((float_t)log10_2lo + log10_2hi);
  71         hi = f - hfsq;
  72         GET_FLOAT_WORD(hx,hi);
  73         SET_FLOAT_WORD(hi,hx&0xfffff000);
  74         lo = (f - hi) - hfsq + r;
  75         return y*log10_2lo + (lo+hi)*ivln10lo + lo*ivln10hi + hi*ivln10hi +
  76             y*log10_2hi;
  77 }