1/*
2 * ====================================================
3 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
4 *
5 * Developed at SunPro, a Sun Microsystems, Inc. business.
6 * Permission to use, copy, modify, and distribute this
7 * software is freely granted, provided that this notice
8 * is preserved.
9 * ====================================================
10 */
11
12/*
13 * double logb(x)
14 * IEEE 754 logb. Included to pass IEEE test suite. Not recommend.
15 * Use ilogb instead.
16 */
17
18#include <float.h>
19
20#include "math.h"
21#include "math_private.h"
22
23static const double
24two54 = 1.80143985094819840000e+16;	/* 43500000 00000000 */
25
26double
27logb(double x)
28{
29	int32_t lx,ix;
30	EXTRACT_WORDS(ix,lx,x);
31	ix &= 0x7fffffff;			/* high |x| */
32	if((ix|lx)==0) return -1.0/fabs(x);
33	if(ix>=0x7ff00000) return x*x;
34	if(ix<0x00100000) {
35		x *= two54;		 /* convert subnormal x to normal */
36		GET_HIGH_WORD(ix,x);
37		ix &= 0x7fffffff;
38		return (double) ((ix>>20)-1023-54);
39	} else
40		return (double) ((ix>>20)-1023);
41}
42
43#if (LDBL_MANT_DIG == 53)
44__weak_reference(logb, logbl);
45#endif
46