1 /*
2 * ====================================================
3 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
4 *
5 * Developed at SunPro, a Sun Microsystems, Inc. business.
6 * Permission to use, copy, modify, and distribute this
7 * software is freely granted, provided that this notice
8 * is preserved.
9 * ====================================================
10 */
11
12 /*
13 * scalbln(double x, long n)
14 * scalbln(x,n) returns x * 2**n computed by exponent
15 * manipulation rather than by actually performing an
16 * exponentiation or a multiplication.
17 */
18
19 #include "math.h"
20 #include "math_private.h"
21 #include <limits.h>
22
23 static const double
24 two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
25 twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
26 huge = 1.0e+300,
27 tiny = 1.0e-300;
28
scalbln(double x,long n)29 double scalbln(double x, long n)
30 {
31 int32_t k, hx, lx;
32
33 EXTRACT_WORDS(hx, lx, x);
34 k = (hx & 0x7ff00000) >> 20; /* extract exponent */
35 if (k == 0) { /* 0 or subnormal x */
36 if ((lx | (hx & 0x7fffffff)) == 0)
37 return x; /* +-0 */
38 x *= two54;
39 GET_HIGH_WORD(hx, x);
40 k = ((hx & 0x7ff00000) >> 20) - 54;
41 }
42 if (k == 0x7ff)
43 return x + x; /* NaN or Inf */
44 k = k + n;
45 if (k > 0x7fe)
46 return huge * copysign(huge, x); /* overflow */
47 if (n < -50000)
48 return tiny * copysign(tiny, x); /* underflow */
49 if (k > 0) { /* normal result */
50 SET_HIGH_WORD(x, (hx & 0x800fffff) | (k << 20));
51 return x;
52 }
53 if (k <= -54) {
54 if (n > 50000) /* in case integer overflow in n+k */
55 return huge * copysign(huge, x); /* overflow */
56 return tiny * copysign(tiny, x); /* underflow */
57 }
58 k += 54; /* subnormal result */
59 SET_HIGH_WORD(x, (hx & 0x800fffff) | (k << 20));
60 return x * twom54;
61 }
62 libm_hidden_def(scalbln)
63
64 #if LONG_MAX == INT_MAX
65 strong_alias_untyped(scalbln,scalbn)
66 #else
67 double scalbn(double x, int n)
68 {
69 return scalbln(x, n);
70 }
71 #endif
72 libm_hidden_def(scalbn)
73