1 /* @(#)s_scalbn.c 5.1 93/09/24 */
2 /*
3 * ====================================================
4 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
5 *
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
9 * is preserved.
10 * ====================================================
11 */
12
13 #ifndef lint
14 static char rcsid[] = "$FreeBSD$";
15 #endif
16
17 /*
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.
22 */
23
24 /*
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.
28 */
29
30 #include <sys/cdefs.h>
31 #include <float.h>
32 #include <math.h>
33
34 #include "fpmath.h"
35
36 #if LDBL_MAX_EXP != 0x4000
37 #error "Unsupported long double format"
38 #endif
39
40 static const long double
41 huge = 0x1p16000L,
42 tiny = 0x1p-16000L;
43
44 long double
scalbnl(long double x,int n)45 scalbnl (long double x, int n)
46 {
47 union IEEEl2bits u;
48 int k;
49 u.e = x;
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 */
53 u.e *= 0x1p+128;
54 k = u.bits.exp - 128;
55 if (n< -50000) return tiny*x; /*underflow*/
56 }
57 if (k==0x7fff) return x+x; /* NaN or Inf */
58 k = k+n;
59 if (k >= 0x7fff) return huge*copysignl(huge,x); /* overflow */
60 if (k > 0) /* normal result */
61 {u.bits.exp = k; return u.e;}
62 if (k <= -128)
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 */
67 u.bits.exp = k;
68 return u.e*0x1p-128;
69 }
70
71 __strong_reference(scalbnl, ldexpl);
72