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 * scalbnl (long double x, int n)
19 * scalbnl(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/*
25 * We assume that a long double has a 15-bit exponent.  On systems
26 * where long double is the same as double, scalbnl() is an alias
27 * for scalbn(), so we don't use this routine.
28 */
29
30#include <sys/cdefs.h>
31#include <float.h>
32#include <math.h>
33
34#include "fpmath.h"
35
36#if LDBL_MAX_EXP != 0x4000
37#error "Unsupported long double format"
38#endif
39
40static const long double
41huge = 0x1p16000L,
42tiny = 0x1p-16000L;
43
44long double
45scalbnl (long double x, int n)
46{
47	union IEEEl2bits u;
48	int k;
49	u.e = x;
50        k = u.bits.exp;				/* extract exponent */
51        if (k==0) {				/* 0 or subnormal x */
52            if ((u.bits.manh|u.bits.manl)==0) return x;	/* +-0 */
53	    u.e *= 0x1p+128;
54	    k = u.bits.exp - 128;
55            if (n< -50000) return tiny*x; 	/*underflow*/
56	    }
57        if (k==0x7fff) return x+x;		/* NaN or Inf */
58        k = k+n;
59        if (k >= 0x7fff) return huge*copysignl(huge,x); /* overflow  */
60        if (k > 0) 				/* normal result */
61	    {u.bits.exp = k; return u.e;}
62        if (k <= -128)
63            if (n > 50000) 	/* in case integer overflow in n+k */
64		return huge*copysign(huge,x);	/*overflow*/
65	    else return tiny*copysign(tiny,x); 	/*underflow*/
66        k += 128;				/* subnormal result */
67	u.bits.exp = k;
68        return u.e*0x1p-128;
69}
70
71__strong_reference(scalbnl, ldexpl);
72