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
25 int
ilogb(double x)26 ilogb(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 }
48 DEF_STD(ilogb);
49 LDBL_MAYBE_CLONE(ilogb);
50