s_logb.c revision 2116 
12116Sjkh/* @(#)s_logb.c 5.1 93/09/24 */
22116Sjkh/*
32116Sjkh * ====================================================
42116Sjkh * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
52116Sjkh *
62116Sjkh * Developed at SunPro, a Sun Microsystems, Inc. business.
72116Sjkh * Permission to use, copy, modify, and distribute this
82116Sjkh * software is freely granted, provided that this notice
92116Sjkh * is preserved.
102116Sjkh * ====================================================
112116Sjkh */
122116Sjkh
132116Sjkh#ifndef lint
142116Sjkhstatic char rcsid[] = "$Id: s_logb.c,v 1.6 1994/08/18 23:07:04 jtc Exp $";
152116Sjkh#endif
162116Sjkh
172116Sjkh/*
182116Sjkh * double logb(x)
192116Sjkh * IEEE 754 logb. Included to pass IEEE test suite. Not recommend.
202116Sjkh * Use ilogb instead.
212116Sjkh */
222116Sjkh
232116Sjkh#include "math.h"
242116Sjkh#include "math_private.h"
252116Sjkh
262116Sjkh#ifdef __STDC__
272116Sjkh	double logb(double x)
282116Sjkh#else
292116Sjkh	double logb(x)
302116Sjkh	double x;
312116Sjkh#endif
322116Sjkh{
332116Sjkh	int32_t lx,ix;
342116Sjkh	EXTRACT_WORDS(ix,lx,x);
352116Sjkh	ix &= 0x7fffffff;			/* high |x| */
362116Sjkh	if((ix|lx)==0) return -1.0/fabs(x);
372116Sjkh	if(ix>=0x7ff00000) return x*x;
382116Sjkh	if((ix>>=20)==0) 			/* IEEE 754 logb */
392116Sjkh		return -1022.0;
402116Sjkh	else
412116Sjkh		return (double) (ix-1023);
422116Sjkh}
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