POK
logb.c
1 /*
2  * POK header
3  *
4  * The following file is a part of the POK project. Any modification should
5  * made according to the POK licence. You CANNOT use this file or a part of
6  * this file is this part of a file for your own project
7  *
8  * For more information on the POK licence, please see our LICENCE FILE
9  *
10  * Please follow the coding guidelines described in doc/CODING_GUIDELINES
11  *
12  * Copyright (c) 2007-2009 POK team
13  *
14  * Created by julien on Fri Jan 30 14:41:34 2009
15  */
16 
17 /* @(#)s_logb.c 5.1 93/09/24 */
18 /*
19  * ====================================================
20  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
21  *
22  * Developed at SunPro, a Sun Microsystems, Inc. business.
23  * Permission to use, copy, modify, and distribute this
24  * software is freely granted, provided that this notice
25  * is preserved.
26  * ====================================================
27  */
28 
29 
30 /*
31  * double logb(x)
32  * IEEE 754 logb. Included to pass IEEE test suite. Not recommend.
33  * Use ilogb instead.
34  */
35 
36 #ifdef POK_NEEDS_LIBMATH
37 
38 #include <libm.h>
39 #include "math_private.h"
40 
41 double
42 logb(double x)
43 {
44  int32_t lx,ix;
45  EXTRACT_WORDS(ix,lx,x);
46  ix &= 0x7fffffff; /* high |x| */
47  if((ix|lx)==0) return -1.0/fabs(x);
48  if(ix>=0x7ff00000) return x*x;
49  if((ix>>=20)==0) /* IEEE 754 logb */
50  return -1022.0;
51  else
52  return (double) (ix-1023);
53 }
54 
55 #endif