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) = 0x80000001
16  * ilogb(inf/NaN) = 0x7fffffff (no signal is raised)
17  */
18 
19 #include <float.h>
20 #include <math.h>
21 
22 #include "math_private.h"
23 
24 int
25 ilogb(double x)
26 {
27 	int32_t hx,lx,ix;
28 
29 	GET_HIGH_WORD(hx,x);
30 	hx &= 0x7fffffff;
31 	if(hx<0x00100000) {
32 	    GET_LOW_WORD(lx,x);
33 	    if((hx|lx)==0)
34 		return 0x80000001;	/* ilogb(0) = 0x80000001 */
35 	    else			/* subnormal x */
36 		if(hx==0) {
37 		    for (ix = -1043; lx>0; lx<<=1) ix -=1;
38 		} else {
39 		    for (ix = -1022,hx<<=11; hx>0; hx<<=1) ix -=1;
40 		}
41 	    return ix;
42 	}
43 	else if (hx<0x7ff00000) return (hx>>20)-1023;
44 	else return 0x7fffffff;
45 }
46 
47 #if	LDBL_MANT_DIG == DBL_MANT_DIG
48 __strong_alias(ilogbl, ilogb);
49 #endif	/* LDBL_MANT_DIG == DBL_MANT_DIG */
50