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 * $FreeBSD: src/lib/msun/src/s_scalbn.c,v 1.6 1999/08/28 00:06:54 peter Exp $
13 * $DragonFly: src/lib/msun/src/Attic/s_scalbn.c,v 1.2 2003/06/17 04:26:53 dillon Exp $
17 * scalbn (double x, int n)
18 * scalbn(x,n) returns x* 2**n computed by exponent
19 * manipulation rather than by actually performing an
20 * exponentiation or a multiplication.
24 #include "math_private.h"
31 two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
32 twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
37 double __generic_scalbn (double x, int n)
39 double __generic_scalbn (x,n)
44 EXTRACT_WORDS(hx,lx,x);
45 k = (hx&0x7ff00000)>>20; /* extract exponent */
46 if (k==0) { /* 0 or subnormal x */
47 if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */
50 k = ((hx&0x7ff00000)>>20) - 54;
51 if (n< -50000) return tiny*x; /*underflow*/
53 if (k==0x7ff) return x+x; /* NaN or Inf */
55 if (k > 0x7fe) return huge*copysign(huge,x); /* overflow */
56 if (k > 0) /* normal result */
57 {SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;}
59 if (n > 50000) /* in case integer overflow in n+k */
60 return huge*copysign(huge,x); /*overflow*/
61 else return tiny*copysign(tiny,x); /*underflow*/
62 k += 54; /* subnormal result */
63 SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20));