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 #include <sys/cdefs.h>
14 #if defined(LIBM_SCCS) && !defined(lint)
15 __RCSID("$NetBSD: s_scalbn.c,v 1.18 2013/05/20 19:40:09 joerg Exp $");
16 #endif
17
18 /*
19 * scalbn (double x, int n)
20 * scalbn(x,n) returns x* 2**n computed by exponent
21 * manipulation rather than by actually performing an
22 * exponentiation or a multiplication.
23 */
24
25 #include "namespace.h"
26 #include "math.h"
27 #include "math_private.h"
28
29 #ifndef _LP64
30 __strong_alias(_scalbn, _scalbln)
31 #endif
32
33 #ifndef __HAVE_LONG_DOUBLE
34 __strong_alias(_scalbnl, _scalbn)
35 __strong_alias(_scalblnl, _scalbln)
36 __weak_alias(scalbnl, _scalbnl)
37 __weak_alias(scalblnl, _scalblnl)
38 #endif
39
40 #ifdef __weak_alias
41 __weak_alias(scalbn, _scalbn)
42 __weak_alias(scalbln, _scalbln)
43 __weak_alias(ldexp, _scalbn)
44 #endif
45
46 static const double
47 two54 = 0x1.0p54, /* 0x43500000, 0x00000000 */
48 twom54 = 0x1.0p-54, /* 0x3C900000, 0x00000000 */
49 huge = 1.0e+300,
50 tiny = 1.0e-300;
51
52 #ifdef _LP64
53 double
scalbn(double x,int n)54 scalbn(double x, int n)
55 {
56 return scalbln(x, n);
57 }
58 #endif
59
60 double
scalbln(double x,long n)61 scalbln(double x, long n)
62 {
63 int32_t k,hx,lx;
64 EXTRACT_WORDS(hx,lx,x);
65 k = ((uint32_t)hx&0x7ff00000)>>20; /* extract exponent */
66 if (k==0) { /* 0 or subnormal x */
67 if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */
68 x *= two54;
69 GET_HIGH_WORD(hx,x);
70 k = (((uint32_t)hx&0x7ff00000)>>20) - 54;
71 if (n< -50000) return tiny*x; /*underflow*/
72 }
73 if (k==0x7ff) return x+x; /* NaN or Inf */
74 k = k+n;
75 if (k > 0x7fe) return huge*copysign(huge,x); /* overflow */
76 if (k > 0) /* normal result */
77 {SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;}
78 if (k <= -54) {
79 if (n > 50000) /* in case integer overflow in n+k */
80 return huge*copysign(huge,x); /*overflow*/
81 else return tiny*copysign(tiny,x); /*underflow*/
82 }
83 k += 54; /* subnormal result */
84 SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20));
85 return x*twom54;
86 }
87