1 | #include "SDL_internal.h" |
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 | /* |
14 | * scalbln(double x, long n) |
15 | * scalbln(x,n) returns x * 2**n computed by exponent |
16 | * manipulation rather than by actually performing an |
17 | * exponentiation or a multiplication. |
18 | */ |
19 | |
20 | #include "math_libm.h" |
21 | #include "math_private.h" |
22 | #include <limits.h> |
23 | |
24 | #ifdef __WATCOMC__ /* Watcom defines huge=__huge */ |
25 | #undef huge |
26 | #endif |
27 | |
28 | static const double |
29 | two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */ |
30 | twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */ |
31 | huge = 1.0e+300, |
32 | tiny = 1.0e-300; |
33 | |
34 | double scalbln(double x, long n) |
35 | { |
36 | int32_t k, hx, lx; |
37 | |
38 | EXTRACT_WORDS(hx, lx, x); |
39 | k = (hx & 0x7ff00000) >> 20; /* extract exponent */ |
40 | if (k == 0) { /* 0 or subnormal x */ |
41 | if ((lx | (hx & 0x7fffffff)) == 0) |
42 | return x; /* +-0 */ |
43 | x *= two54; |
44 | GET_HIGH_WORD(hx, x); |
45 | k = ((hx & 0x7ff00000) >> 20) - 54; |
46 | } |
47 | if (k == 0x7ff) |
48 | return x + x; /* NaN or Inf */ |
49 | k = (int32_t)(k + n); |
50 | if (k > 0x7fe) |
51 | return huge * copysign(huge, x); /* overflow */ |
52 | if (n < -50000) |
53 | return tiny * copysign(tiny, x); /* underflow */ |
54 | if (k > 0) { /* normal result */ |
55 | SET_HIGH_WORD(x, (hx & 0x800fffff) | (k << 20)); |
56 | return x; |
57 | } |
58 | if (k <= -54) { |
59 | if (n > 50000) /* in case integer overflow in n+k */ |
60 | return huge * copysign(huge, x); /* overflow */ |
61 | return tiny * copysign(tiny, x); /* underflow */ |
62 | } |
63 | k += 54; /* subnormal result */ |
64 | SET_HIGH_WORD(x, (hx & 0x800fffff) | (k << 20)); |
65 | return x * twom54; |
66 | } |
67 | libm_hidden_def(scalbln) |
68 | |
69 | |
70 | double scalbn(double x, int n) |
71 | { |
72 | return scalbln(x, n); |
73 | } |
74 | libm_hidden_def(scalbn) |
75 | |