Atlas - s_scalbn.c
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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_libm.h"
20#include "math_private.h"
21#include <limits.h>
22
23static const double
24two54  = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
25twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
26huge   = 1.0e+300,
27tiny   = 1.0e-300;
28
29double 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}
62libm_hidden_def(scalbln)
63
64
65double scalbn(double x, int n)
66{
67	return scalbln(x, n);
68}
69libm_hidden_def(scalbn)
70
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