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[] = "$FreeBSD$";
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.
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.
30 #include <sys/cdefs.h>
36 #if LDBL_MAX_EXP != 0x4000
37 #error "Unsupported long double format"
40 static const long double
45 scalbnl (long double x, int n)
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 */
55 if (n< -50000) return tiny*x; /*underflow*/
57 if (k==0x7fff) return x+x; /* NaN or Inf */
59 if (k >= 0x7fff) return huge*copysignl(huge,x); /* overflow */
60 if (k > 0) /* normal result */
61 {u.bits.exp = k; return u.e;}
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 */
71 __strong_reference(scalbnl, ldexpl);