1*05a0b428SJohn Marino /* @(#)s_ilogb.c 5.1 93/09/24 */
2*05a0b428SJohn Marino /*
3*05a0b428SJohn Marino * ====================================================
4*05a0b428SJohn Marino * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
5*05a0b428SJohn Marino *
6*05a0b428SJohn Marino * Developed at SunPro, a Sun Microsystems, Inc. business.
7*05a0b428SJohn Marino * Permission to use, copy, modify, and distribute this
8*05a0b428SJohn Marino * software is freely granted, provided that this notice
9*05a0b428SJohn Marino * is preserved.
10*05a0b428SJohn Marino * ====================================================
11*05a0b428SJohn Marino */
12*05a0b428SJohn Marino
13*05a0b428SJohn Marino /* ilogb(double x)
14*05a0b428SJohn Marino * return the binary exponent of non-zero x
15*05a0b428SJohn Marino * ilogb(0) = 0x80000001
16*05a0b428SJohn Marino * ilogb(inf/NaN) = 0x7fffffff (no signal is raised)
17*05a0b428SJohn Marino */
18*05a0b428SJohn Marino
19*05a0b428SJohn Marino #include <float.h>
20*05a0b428SJohn Marino #include <math.h>
21*05a0b428SJohn Marino
22*05a0b428SJohn Marino #include "math_private.h"
23*05a0b428SJohn Marino
24*05a0b428SJohn Marino int
ilogb(double x)25*05a0b428SJohn Marino ilogb(double x)
26*05a0b428SJohn Marino {
27*05a0b428SJohn Marino int32_t hx,lx,ix;
28*05a0b428SJohn Marino
29*05a0b428SJohn Marino GET_HIGH_WORD(hx,x);
30*05a0b428SJohn Marino hx &= 0x7fffffff;
31*05a0b428SJohn Marino if(hx<0x00100000) {
32*05a0b428SJohn Marino GET_LOW_WORD(lx,x);
33*05a0b428SJohn Marino if((hx|lx)==0)
34*05a0b428SJohn Marino return 0x80000001; /* ilogb(0) = 0x80000001 */
35*05a0b428SJohn Marino else /* subnormal x */
36*05a0b428SJohn Marino if(hx==0) {
37*05a0b428SJohn Marino for (ix = -1043; lx>0; lx<<=1) ix -=1;
38*05a0b428SJohn Marino } else {
39*05a0b428SJohn Marino for (ix = -1022,hx<<=11; hx>0; hx<<=1) ix -=1;
40*05a0b428SJohn Marino }
41*05a0b428SJohn Marino return ix;
42*05a0b428SJohn Marino }
43*05a0b428SJohn Marino else if (hx<0x7ff00000) return (hx>>20)-1023;
44*05a0b428SJohn Marino else return 0x7fffffff;
45*05a0b428SJohn Marino }
46*05a0b428SJohn Marino
47*05a0b428SJohn Marino #if LDBL_MANT_DIG == DBL_MANT_DIG
48*05a0b428SJohn Marino __strong_alias(ilogbl, ilogb);
49*05a0b428SJohn Marino #endif /* LDBL_MANT_DIG == DBL_MANT_DIG */
50