1 /* @(#)s_logb.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 #ifndef lint
14 static char rcsid[] = "$FreeBSD: src/lib/msun/src/s_logb.c,v 1.10 2005/12/03 11:57:19 bde Exp $";
15 #endif
16
17 /*
18 * double logb(x)
19 * IEEE 754 logb. Included to pass IEEE test suite. Not recommend.
20 * Use ilogb instead.
21 */
22
23 #include "math.h"
24 #include "math_private.h"
25
26 static const double
27 two54 = 1.80143985094819840000e+16; /* 43500000 00000000 */
28
29 double
logb(double x)30 logb(double x)
31 {
32 int32_t lx,ix;
33 EXTRACT_WORDS(ix,lx,x);
34 ix &= 0x7fffffff; /* high |x| */
35 if((ix|lx)==0) return -1.0/fabs(x);
36 if(ix>=0x7ff00000) return x*x;
37 if(ix<0x00100000) {
38 x *= two54; /* convert subnormal x to normal */
39 GET_HIGH_WORD(ix,x);
40 ix &= 0x7fffffff;
41 return (double) ((ix>>20)-1023-54);
42 } else
43 return (double) ((ix>>20)-1023);
44 }
45