/* @(#)s_ilogb.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.
 * ====================================================
 */

/* ilogb(double x)
 * return the binary exponent of non-zero x
 * ilogb(0) = 0x80000001
 * ilogb(inf/NaN) = 0x7fffffff (no signal is raised)
 */

#include "math.h"

int ilogb(double x) {
	int hx, lx, ix;

	hx = (__HI(x)) & 0x7fffffff; /* high word of x */
	if(hx < 0x00100000) {
		lx = __LO(x);
		if((hx | lx) == 0)
			return 0x80000001; /* ilogb(0) = 0x80000001 */
		else			   /* subnormal x */
			if(hx == 0) {
				for(ix = -1043; lx > 0; lx <<= 1) ix -= 1;
			} else {
				for(ix = -1022, hx <<= 11; hx > 0; hx <<= 1) ix -= 1;
			}
		return ix;
	} else if(hx < 0x7ff00000)
		return (hx >> 20) - 1023;
	else
		return 0x7fffffff;
}