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 #include <sys/cdefs.h>
14 __FBSDID("$FreeBSD$");
15
16 /*
17 * double logb(x)
18 * IEEE 754 logb. Included to pass IEEE test suite. Not recommend.
19 * Use ilogb instead.
20 */
21
22 #include <float.h>
23
24 #include "math.h"
25 #include "math_private.h"
26
27 static const double
28 two54 = 1.80143985094819840000e+16; /* 43500000 00000000 */
29
30 double
logb(double x)31 logb(double x)
32 {
33 int32_t lx,ix;
34 EXTRACT_WORDS(ix,lx,x);
35 ix &= 0x7fffffff; /* high |x| */
36 if((ix|lx)==0) return -1.0/fabs(x);
37 if(ix>=0x7ff00000) return x*x;
38 if(ix<0x00100000) {
39 x *= two54; /* convert subnormal x to normal */
40 GET_HIGH_WORD(ix,x);
41 ix &= 0x7fffffff;
42 return (double) ((ix>>20)-1023-54);
43 } else
44 return (double) ((ix>>20)-1023);
45 }
46
47 #if (LDBL_MANT_DIG == 53)
48 __weak_reference(logb, logbl);
49 #endif
50