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
14static char rcsid[] = "$FreeBSD$";
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 <sys/cdefs.h>
25#include <float.h>
26
27#include "math.h"
28#include "math_private.h"
29
30static const double
31two54   =  1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
32twom54  =  5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
33huge   = 1.0e+300,
34tiny   = 1.0e-300;
35
36double
37scalbn (double x, int n)
38{
39	int32_t k,hx,lx;
40	EXTRACT_WORDS(hx,lx,x);
41        k = (hx&0x7ff00000)>>20;		/* extract exponent */
42        if (k==0) {				/* 0 or subnormal x */
43            if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */
44	    x *= two54;
45	    GET_HIGH_WORD(hx,x);
46	    k = ((hx&0x7ff00000)>>20) - 54;
47            if (n< -50000) return tiny*x; 	/*underflow*/
48	    }
49        if (k==0x7ff) return x+x;		/* NaN or Inf */
50        k = k+n;
51        if (k >  0x7fe) return huge*copysign(huge,x); /* overflow  */
52        if (k > 0) 				/* normal result */
53	    {SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;}
54        if (k <= -54)
55            if (n > 50000) 	/* in case integer overflow in n+k */
56		return huge*copysign(huge,x);	/*overflow*/
57	    else return tiny*copysign(tiny,x); 	/*underflow*/
58        k += 54;				/* subnormal result */
59	SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20));
60        return x*twom54;
61}
62
63#if (LDBL_MANT_DIG == 53)
64__weak_reference(scalbn, ldexpl);
65__weak_reference(scalbn, scalbnl);
66#endif
67