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#if defined(LIBM_SCCS) && !defined(lint)
14static char rcsid[] = "$NetBSD: s_scalbn.c,v 1.8 1995/05/10 20:48:08 jtc 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__
28static const double
29#else
30static double
31#endif
32two54   =  1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
33twom54  =  5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
34huge   = 1.0e+300,
35tiny   = 1.0e-300;
36
37#ifdef __STDC__
38	double __scalbln (double x, long int n)
39#else
40	double __scalbln (x,n)
41	double x; long 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	    }
53        if (k==0x7ff) return x+x;		/* NaN or Inf */
54        k = k+n;
55        if (n> 50000 || k >  0x7fe)
56	  return huge*__copysign(huge,x); /* overflow  */
57	if (n< -50000) return tiny*__copysign(tiny,x); /*underflow*/
58        if (k > 0) 				/* normal result */
59	    {SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;}
60        if (k <= -54)
61	  return tiny*__copysign(tiny,x); 	/*underflow*/
62        k += 54;				/* subnormal result */
63	SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20));
64        return x*twom54;
65}
66weak_alias (__scalbln, scalbln)
67#ifdef NO_LONG_DOUBLE
68strong_alias (__scalbln, __scalblnl)
69weak_alias (__scalbln, scalblnl)
70#endif
71