1 /* @(#)s_scalbn.c 5.1 93/09/24 */
3 * ====================================================
4 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
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
10 * ====================================================
12 * $NetBSD: s_scalbn.c,v 1.15 2011/07/26 16:10:16 joerg Exp $
16 * scalbn (double x, int n)
17 * scalbn(x,n) returns x* 2**n computed by exponent
18 * manipulation rather than by actually performing an
19 * exponentiation or a multiplication.
23 #include "math_private.h"
26 two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
27 twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
32 scalbn(double x, int n)
35 EXTRACT_WORDS(hx,lx,x);
36 k = ((uint32_t)hx&0x7ff00000)>>20; /* extract exponent */
37 if (k==0) { /* 0 or subnormal x */
38 if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */
41 k = (((uint32_t)hx&0x7ff00000)>>20) - 54;
42 if (n< -50000) return tiny*x; /*underflow*/
44 if (k==0x7ff) return x+x; /* NaN or Inf */
46 if (k > 0x7fe) return huge*copysign(huge,x); /* overflow */
47 if (k > 0) /* normal result */
48 {SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;}
50 if (n > 50000) /* in case integer overflow in n+k */
51 return huge*copysign(huge,x); /*overflow*/
52 else return tiny*copysign(tiny,x); /*underflow*/
54 k += 54; /* subnormal result */
55 SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20));