Subversion Repositories shark

Rev

Rev 1618 | Details | Compare with Previous | Last modification | View Log | RSS feed

Rev Author Line No. Line
2 pj 1
/* @(#)s_scalbn.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[] = "$\Id: s_scalbn.c,v 1.2.6.1 1997/02/23 11:03:21 joerg Exp $";
15
#endif
16
 
17
/*
18
 * scalbn (double x, int n)
19
 * scalbn(x,n) returns x* 2**n  computed by  exponent
20
 * manipulation rather than by actually performing an
21
 * exponentiation or a multiplication.
22
 */
23
 
24
#include "math.h"
25
#include "math_private.h"
26
 
27
#ifdef __STDC__
28
static const double
29
#else
30
static double
31
#endif
32
two54   =  1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
33
twom54  =  5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
34
huge   = 1.0e+300,
35
tiny   = 1.0e-300;
36
 
37
#ifdef __STDC__
38
        double __generic_scalbn (double x, int n)
39
#else
40
        double __generic_scalbn (x,n)
41
        double x; int n;
42
#endif
43
{
44
        int32_t k,hx,lx;
45
        EXTRACT_WORDS(hx,lx,x);
46
        k = (hx&0x7ff00000)>>20;                /* extract exponent */
47
        if (k==0) {                             /* 0 or subnormal x */
48
            if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */
49
            x *= two54;
50
            GET_HIGH_WORD(hx,x);
51
            k = ((hx&0x7ff00000)>>20) - 54;
52
            if (n< -50000) return tiny*x;       /*underflow*/
53
            }
54
        if (k==0x7ff) return x+x;               /* NaN or Inf */
55
        k = k+n;
56
        if (k >  0x7fe) return huge*copysign(huge,x); /* overflow  */
57
        if (k > 0)                              /* normal result */
58
            {SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;}
59
        if (k <= -54)
60
            if (n > 50000)      /* in case integer overflow in n+k */
61
                return huge*copysign(huge,x);   /*overflow*/
62
            else return tiny*copysign(tiny,x);  /*underflow*/
63
        k += 54;                                /* subnormal result */
64
        SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20));
65
        return x*twom54;
66
}