SDL  2.0
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 
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 
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 
65 double scalbn(double x, int n)
66 {
67  return scalbln(x, n);
68 }
69 libm_hidden_def(scalbn)