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      1 /* e_log10f.c -- float version of e_log10.c.
      2  * Conversion to float by Ian Lance Taylor, Cygnus Support, ian (at) 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 <sys/cdefs.h>
     17 #if defined(LIBM_SCCS) && !defined(lint)
     18 __RCSID("$NetBSD: e_log10f.c,v 1.8 2002/05/26 22:01:51 wiz Exp $");
     19 #endif
     20 
     21 #include "math.h"
     22 #include "math_private.h"
     23 
     24 static const float
     25 two25      =  3.3554432000e+07, /* 0x4c000000 */
     26 ivln10     =  4.3429449201e-01, /* 0x3ede5bd9 */
     27 log10_2hi  =  3.0102920532e-01, /* 0x3e9a2080 */
     28 log10_2lo  =  7.9034151668e-07; /* 0x355427db */
     29 
     30 static const float zero   =  0.0;
     31 
     32 float
     33 __ieee754_log10f(float x)
     34 {
     35 	float y,z;
     36 	int32_t i,k,hx;
     37 
     38 	GET_FLOAT_WORD(hx,x);
     39 
     40         k=0;
     41         if (hx < 0x00800000) {                  /* x < 2**-126  */
     42             if ((hx&0x7fffffff)==0)
     43                 return -two25/zero;             /* log(+-0)=-inf */
     44             if (hx<0) return (x-x)/zero;        /* log(-#) = NaN */
     45             k -= 25; x *= two25; /* subnormal number, scale up x */
     46 	    GET_FLOAT_WORD(hx,x);
     47         }
     48 	if (hx >= 0x7f800000) return x+x;
     49 	k += (hx>>23)-127;
     50 	i  = ((u_int32_t)k&0x80000000)>>31;
     51         hx = (hx&0x007fffff)|((0x7f-i)<<23);
     52         y  = (float)(k+i);
     53 	SET_FLOAT_WORD(x,hx);
     54 	z  = y*log10_2lo + ivln10*__ieee754_logf(x);
     55 	return  z+y*log10_2hi;
     56 }
     57