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/* @(#)s_logb.c 5.1 93/09/24 */
/*
* ====================================================
* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
*
* Developed at SunPro, a Sun Microsystems, Inc. business.
* Permission to use, copy, modify, and distribute this
* software is freely granted, provided that this notice
* is preserved.
* ====================================================
*/
#ifndef lint
static char rcsid[] = "$Id: s_logb.c,v 1.4 1994/03/03 17:04:41 jtc Exp $";
#endif
/*
* double logb(x)
* IEEE 754 logb. Included to pass IEEE test suite. Not recommend.
* Use ilogb instead.
*/
#include <math.h>
#include <machine/endian.h>
#if BYTE_ORDER == LITTLE_ENDIAN
#define n0 1
#else
#define n0 0
#endif
#ifdef __STDC__
double logb(double x)
#else
double logb(x)
double x;
#endif
{
int lx,ix;
ix = (*(n0+(int*)&x))&0x7fffffff; /* high |x| */
lx = *(1-n0+(int*)&x); /* low x */
if((ix|lx)==0) return -1.0/fabs(x);
if(ix>=0x7ff00000) return x*x;
if((ix>>=20)==0) /* IEEE 754 logb */
return -1022.0;
else
return (double) (ix-1023);
}
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