12116Sjkh/* @(#)s_ilogb.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
88870Srgrimes * software is freely granted, provided that this notice
92116Sjkh * is preserved.
102116Sjkh * ====================================================
112116Sjkh */
122116Sjkh
13176451Sdas#include <sys/cdefs.h>
14176451Sdas__FBSDID("$FreeBSD$");
152116Sjkh
162116Sjkh/* ilogb(double x)
172116Sjkh * return the binary exponent of non-zero x
18136332Sstefanf * ilogb(0) = FP_ILOGB0
19136332Sstefanf * ilogb(NaN) = FP_ILOGBNAN (no signal is raised)
20136332Sstefanf * ilogb(inf) = INT_MAX (no signal is raised)
212116Sjkh */
222116Sjkh
23136332Sstefanf#include <limits.h>
24136332Sstefanf
252116Sjkh#include "math.h"
262116Sjkh#include "math_private.h"
272116Sjkh
28117912Speter	int ilogb(double x)
292116Sjkh{
302116Sjkh	int32_t hx,lx,ix;
312116Sjkh
322116Sjkh	EXTRACT_WORDS(hx,lx,x);
332116Sjkh	hx &= 0x7fffffff;
342116Sjkh	if(hx<0x00100000) {
358870Srgrimes	    if((hx|lx)==0)
36136332Sstefanf		return FP_ILOGB0;
372116Sjkh	    else			/* subnormal x */
382116Sjkh		if(hx==0) {
392116Sjkh		    for (ix = -1043; lx>0; lx<<=1) ix -=1;
402116Sjkh		} else {
412116Sjkh		    for (ix = -1022,hx<<=11; hx>0; hx<<=1) ix -=1;
422116Sjkh		}
432116Sjkh	    return ix;
442116Sjkh	}
452116Sjkh	else if (hx<0x7ff00000) return (hx>>20)-1023;
46136332Sstefanf	else if (hx>0x7ff00000 || lx!=0) return FP_ILOGBNAN;
47136332Sstefanf	else return INT_MAX;
482116Sjkh}
49