1 /* s_scalbnl.c -- long double version of s_scalbn.c.
2 */
3
4 /* @(#)s_scalbn.c 5.1 93/09/24 */
5 /*
6 * ====================================================
7 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
8 *
9 * Developed at SunPro, a Sun Microsystems, Inc. business.
10 * Permission to use, copy, modify, and distribute this
11 * software is freely granted, provided that this notice
12 * is preserved.
13 * ====================================================
14 */
15
16 #if defined(LIBM_SCCS) && !defined(lint)
17 static char rcsid[] = "$NetBSD: $";
18 #endif
19
20 /*
21 * scalbnl (long double x, int n)
22 * scalbnl(x,n) returns x* 2**n computed by exponent
23 * manipulation rather than by actually performing an
24 * exponentiation or a multiplication.
25 */
26
27 #include <math.h>
28 #include <math_private.h>
29 #include <math_ldbl_opt.h>
30
31 static const long double
32 twolm54 = 5.55111512312578270212e-17, /* 0x3C90000000000000, 0 */
33 huge = 1.0E+300L,
34 tiny = 1.0E-300L;
35 static const double
36 two54 = 1.80143985094819840000e+16, /* 0x4350000000000000 */
37 twom54 = 5.55111512312578270212e-17; /* 0x3C90000000000000 */
38
__scalbnl(long double x,int n)39 long double __scalbnl (long double x, int n)
40 {
41 int64_t k,l,hx,lx;
42 union { int64_t i; double d; } u;
43 double xhi, xlo;
44
45 ldbl_unpack (x, &xhi, &xlo);
46 EXTRACT_WORDS64 (hx, xhi);
47 EXTRACT_WORDS64 (lx, xlo);
48 k = (hx>>52)&0x7ff; /* extract exponent */
49 l = (lx>>52)&0x7ff;
50 if (k==0) { /* 0 or subnormal x */
51 if ((hx&0x7fffffffffffffffULL)==0) return x; /* +-0 */
52 u.i = hx;
53 u.d *= two54;
54 hx = u.i;
55 k = ((hx>>52)&0x7ff) - 54;
56 }
57 else if (k==0x7ff) return x+x; /* NaN or Inf */
58 if (n< -50000) return tiny*copysignl(tiny,x); /*underflow */
59 if (n> 50000 || k+n > 0x7fe)
60 return huge*copysignl(huge,x); /* overflow */
61 /* Now k and n are bounded we know that k = k+n does not
62 overflow. */
63 k = k+n;
64 if (k > 0) { /* normal result */
65 hx = (hx&0x800fffffffffffffULL)|(k<<52);
66 if ((lx & 0x7fffffffffffffffULL) == 0) { /* low part +-0 */
67 INSERT_WORDS64 (xhi, hx);
68 INSERT_WORDS64 (xlo, lx);
69 x = ldbl_pack (xhi, xlo);
70 return x;
71 }
72 if (l == 0) { /* low part subnormal */
73 u.i = lx;
74 u.d *= two54;
75 lx = u.i;
76 l = ((lx>>52)&0x7ff) - 54;
77 }
78 l = l + n;
79 if (l > 0)
80 lx = (lx&0x800fffffffffffffULL)|(l<<52);
81 else if (l <= -54)
82 lx = (lx&0x8000000000000000ULL);
83 else {
84 l += 54;
85 u.i = (lx&0x800fffffffffffffULL)|(l<<52);
86 u.d *= twom54;
87 lx = u.i;
88 }
89 INSERT_WORDS64 (xhi, hx);
90 INSERT_WORDS64 (xlo, lx);
91 x = ldbl_pack (xhi, xlo);
92 return x;
93 }
94 if (k <= -54)
95 return tiny*copysignl(tiny,x); /*underflow*/
96 k += 54; /* subnormal result */
97 lx &= 0x8000000000000000ULL;
98 hx &= 0x800fffffffffffffULL;
99 INSERT_WORDS64 (xhi, hx|(k<<52));
100 INSERT_WORDS64 (xlo, lx);
101 x = ldbl_pack (xhi, xlo);
102 return x*twolm54;
103 }
104