/* @(#)s_logb.c 1.3 95/01/18 */
/*
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * Developed at SunSoft, a Sun Microsystems, Inc. business.
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice
 * is preserved.
 * ====================================================
 */

/*
 * double logb(x)
 * IEEE 754 logb. Included to pass IEEE test suite. Not recommend.
 * Use ilogb instead.
 */

#include "math.h"

double logb(double x) {
	int lx, ix;
	ix = (__HI(x)) & 0x7fffffff; /* high |x| */
	lx = __LO(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);
}