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 * ====================================================
14 static char rcsid[] = "$Id$";
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.
25 #include "math_private.h"
32 two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
33 twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
38 double __generic_scalbn (double x, int n)
40 double __generic_scalbn (x,n)
45 EXTRACT_WORDS(hx,lx,x);
46 k = (hx&0x7ff00000)>>20; /* extract exponent */
47 if (k==0) { /* 0 or subnormal x */
48 if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */
51 k = ((hx&0x7ff00000)>>20) - 54;
52 if (n< -50000) return tiny*x; /*underflow*/
54 if (k==0x7ff) return x+x; /* NaN or Inf */
56 if (k > 0x7fe) return huge*copysign(huge,x); /* overflow */
57 if (k > 0) /* normal result */
58 {SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;}
60 if (n > 50000) /* in case integer overflow in n+k */
61 return huge*copysign(huge,x); /*overflow*/
62 else return tiny*copysign(tiny,x); /*underflow*/
63 k += 54; /* subnormal result */
64 SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20));