1/* @(#)s_ilogb.c 5.1 93/09/24 */
2/*
3 * ====================================================
4 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
5 *
6 * Developed at SunPro, a Sun Microsystems, Inc. business.
7 * Permission to use, copy, modify, and distribute this
8 * software is freely granted, provided that this notice
9 * is preserved.
10 * ====================================================
11 */
12
13/* ilogb(double x)
14 * return the binary exponent of non-zero x
15 * ilogb(0) = FP_ILOGB0
16 * ilogb(NaN) = FP_ILOGBNAN (no signal is raised)
17 * ilogb(inf) = INT_MAX (no signal is raised)
18 */
19
20#include <float.h>
21#include <math.h>
22
23#include "math_private.h"
24
25int
26ilogb(double x)
27{
28	int32_t hx,lx,ix;
29
30	GET_HIGH_WORD(hx,x);
31	hx &= 0x7fffffff;
32	if(hx<0x00100000) {
33	    GET_LOW_WORD(lx,x);
34	    if((hx|lx)==0)
35		return FP_ILOGB0;	/* ilogb(0) = FP_ILOGB0 */
36	    else			/* subnormal x */
37		if(hx==0) {
38		    for (ix = -1043; lx>0; lx<<=1) ix -=1;
39		} else {
40		    for (ix = -1022,hx<<=11; hx>0; hx<<=1) ix -=1;
41		}
42	    return ix;
43	}
44	else if (hx<0x7ff00000) return (hx>>20)-1023;
45	else if (hx>0x7ff00000 || lx!=0) return FP_ILOGBNAN;
46	else return INT_MAX;
47}
48DEF_STD(ilogb);
49LDBL_MAYBE_CLONE(ilogb);
50