1
2/* @(#)s_scalbn.c 1.3 95/01/18 */
3/*
4 * ====================================================
5 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
6 *
7 * Developed at SunSoft, a Sun Microsystems, Inc. business.
8 * Permission to use, copy, modify, and distribute this
9 * software is freely granted, provided that this notice
10 * is preserved.
11 * ====================================================
12 */
13
14/*
15 * ieee_scalbn (double x, int n)
16 * ieee_scalbn(x,n) returns x* 2**n  computed by  exponent
17 * manipulation rather than by actually performing an
18 * exponentiation or a multiplication.
19 */
20
21#include "fdlibm.h"
22
23#ifdef __STDC__
24static const double
25#else
26static double
27#endif
28two54   =  1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
29twom54  =  5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
30huge   = 1.0e+300,
31tiny   = 1.0e-300;
32
33#ifdef __STDC__
34	double ieee_scalbn (double x, int n)
35#else
36	double ieee_scalbn (x,n)
37	double x; int n;
38#endif
39{
40	int  k,hx,lx;
41	hx = __HI(x);
42	lx = __LO(x);
43        k = (hx&0x7ff00000)>>20;		/* extract exponent */
44        if (k==0) {				/* 0 or subnormal x */
45            if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */
46	    x *= two54;
47	    hx = __HI(x);
48	    k = ((hx&0x7ff00000)>>20) - 54;
49            if (n< -50000) return tiny*x; 	/*underflow*/
50	    }
51        if (k==0x7ff) return x+x;		/* NaN or Inf */
52        k = k+n;
53        if (k >  0x7fe) return huge*ieee_copysign(huge,x); /* overflow  */
54        if (k > 0) 				/* normal result */
55	    {__HI(x) = (hx&0x800fffff)|(k<<20); return x;}
56        if (k <= -54)
57            if (n > 50000) 	/* in case integer overflow in n+k */
58		return huge*ieee_copysign(huge,x);	/*overflow*/
59	    else return tiny*ieee_copysign(tiny,x); 	/*underflow*/
60        k += 54;				/* subnormal result */
61        __HI(x) = (hx&0x800fffff)|(k<<20);
62        return x*twom54;
63}
64