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 1.19 2018/03/27 11:59:49 martin 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 __weak_alias(ldexpl, _scalblnl)
39 #endif
40
41 #ifdef __weak_alias
42 __weak_alias(scalbn, _scalbn)
43 __weak_alias(scalbln, _scalbln)
44 __weak_alias(ldexp, _scalbn)
45 #endif
46
47 static const double
48 two54 = 0x1.0p54, /* 0x43500000, 0x00000000 */
49 twom54 = 0x1.0p-54, /* 0x3C900000, 0x00000000 */
50 huge = 1.0e+300,
51 tiny = 1.0e-300;
52
53 #ifdef _LP64
54 double
scalbn(double x,int n)55 scalbn(double x, int n)
56 {
57 return scalbln(x, n);
58 }
59 #endif
60
61 double
scalbln(double x,long n)62 scalbln(double x, long n)
63 {
64 int32_t k,hx,lx;
65 EXTRACT_WORDS(hx,lx,x);
66 k = ((uint32_t)hx&0x7ff00000)>>20; /* extract exponent */
67 if (k==0) { /* 0 or subnormal x */
68 if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */
69 x *= two54;
70 GET_HIGH_WORD(hx,x);
71 k = (((uint32_t)hx&0x7ff00000)>>20) - 54;
72 if (n< -50000) return tiny*x; /*underflow*/
73 }
74 if (k==0x7ff) return x+x; /* NaN or Inf */
75 k = k+n;
76 if (k > 0x7fe) return huge*copysign(huge,x); /* overflow */
77 if (k > 0) /* normal result */
78 {SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;}
79 if (k <= -54) {
80 if (n > 50000) /* in case integer overflow in n+k */
81 return huge*copysign(huge,x); /*overflow*/
82 else return tiny*copysign(tiny,x); /*underflow*/
83 }
84 k += 54; /* subnormal result */
85 SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20));
86 return x*twom54;
87 }
88