e_log10f.c revision 219361 
12116Sjkh/*
22116Sjkh * ====================================================
32116Sjkh * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
42116Sjkh *
52116Sjkh * Developed at SunPro, a Sun Microsystems, Inc. business.
62116Sjkh * Permission to use, copy, modify, and distribute this
78870Srgrimes * software is freely granted, provided that this notice
82116Sjkh * is preserved.
92116Sjkh * ====================================================
102116Sjkh */
112116Sjkh
12176451Sdas#include <sys/cdefs.h>
13176451Sdas__FBSDID("$FreeBSD: head/lib/msun/src/e_log10f.c 219361 2011-03-07 03:12:08Z das $");
142116Sjkh
15219361Sdas/*
16219361Sdas * Return the base 10 logarithm of x. See k_log.c for details on the algorithm.
17219361Sdas */
18219361Sdas
192116Sjkh#include "math.h"
202116Sjkh#include "math_private.h"
21219361Sdas#include "k_logf.h"
222116Sjkh
232116Sjkhstatic const float
242116Sjkhtwo25      =  3.3554432000e+07, /* 0x4c000000 */
25219361Sdasivln10hi   =  4.3432617188e-01, /* 0x3ede6000 */
26219361Sdasivln10lo   = -3.1689971365e-05, /* 0xb804ead9 */
272116Sjkhlog10_2hi  =  3.0102920532e-01, /* 0x3e9a2080 */
282116Sjkhlog10_2lo  =  7.9034151668e-07; /* 0x355427db */
292116Sjkh
302116Sjkhstatic const float zero   =  0.0;
312116Sjkh
3297413Salfredfloat
3397413Salfred__ieee754_log10f(float x)
342116Sjkh{
35219361Sdas	float f,hi,lo,y,z;
362116Sjkh	int32_t i,k,hx;
372116Sjkh
382116Sjkh	GET_FLOAT_WORD(hx,x);
392116Sjkh
402116Sjkh        k=0;
412116Sjkh        if (hx < 0x00800000) {                  /* x < 2**-126  */
422116Sjkh            if ((hx&0x7fffffff)==0)
432116Sjkh                return -two25/zero;             /* log(+-0)=-inf */
442116Sjkh            if (hx<0) return (x-x)/zero;        /* log(-#) = NaN */
452116Sjkh            k -= 25; x *= two25; /* subnormal number, scale up x */
462116Sjkh	    GET_FLOAT_WORD(hx,x);
472116Sjkh        }
482116Sjkh	if (hx >= 0x7f800000) return x+x;
492116Sjkh	k += (hx>>23)-127;
50219361Sdas	hx &= 0x007fffff;
51219361Sdas	i = (hx+(0x4afb0d))&0x800000;
52219361Sdas	SET_FLOAT_WORD(x,hx|(i^0x3f800000));	/* normalize x or x/2 */
53219361Sdas	k += (i>>23);
54219361Sdas	y = (float)k;
55219361Sdas	f = __kernel_logf(x);
56219361Sdas	x = x - (float)1.0;
57219361Sdas	GET_FLOAT_WORD(hx,x);
58219361Sdas	SET_FLOAT_WORD(hi,hx&0xfffff000);
59219361Sdas	lo = x - hi;
60219361Sdas	z = y*log10_2lo + (x+f)*ivln10lo + (lo+f)*ivln10hi + hi*ivln10hi;
612116Sjkh	return  z+y*log10_2hi;
622116Sjkh}
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