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1 | // std::tr1::hash definitions, long double bits -*- C++ -*- |
2 | ||
a5544970 | 3 | // Copyright (C) 2010-2019 Free Software Foundation, Inc. |
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4 | // |
5 | // This file is part of the GNU ISO C++ Library. This library is free | |
6 | // software; you can redistribute it and/or modify it under the | |
7 | // terms of the GNU General Public License as published by the | |
8 | // Free Software Foundation; either version 3, or (at your option) | |
9 | // any later version. | |
10 | ||
11 | // This library is distributed in the hope that it will be useful, | |
12 | // but WITHOUT ANY WARRANTY; without even the implied warranty of | |
13 | // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
14 | // GNU General Public License for more details. | |
15 | ||
16 | // Under Section 7 of GPL version 3, you are granted additional | |
17 | // permissions described in the GCC Runtime Library Exception, version | |
18 | // 3.1, as published by the Free Software Foundation. | |
19 | ||
20 | // You should have received a copy of the GNU General Public License and | |
21 | // a copy of the GCC Runtime Library Exception along with this program; | |
22 | // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see | |
23 | // <http://www.gnu.org/licenses/>. | |
24 | ||
d56a3683 JW |
25 | #pragma GCC diagnostic ignored "-Wattribute-alias" |
26 | ||
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27 | namespace std _GLIBCXX_VISIBILITY(default) |
28 | { | |
f92ab29f | 29 | namespace tr1 |
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30 | { |
31 | // For long double, careful with random padding bits (e.g., on x86, | |
32 | // 10 bytes -> 12 bytes) and resort to frexp. | |
33 | template<> | |
34 | size_t | |
35 | hash<long double>::operator()(long double __val) const | |
36 | { | |
37 | // 0 and -0 both hash to zero. | |
38 | if (__val == 0.0L) | |
39 | return 0; | |
40 | ||
41 | int __exponent; | |
42 | __val = __builtin_frexpl(__val, &__exponent); | |
43 | __val = __val < 0.0l ? -(__val + 0.5l) : __val; | |
44 | ||
45 | const long double __mult = __SIZE_MAX__ + 1.0l; | |
46 | __val *= __mult; | |
47 | ||
48 | // Try to use all the bits of the mantissa (really necessary only | |
49 | // on 32-bit targets, at least for 80-bit floating point formats). | |
50 | const size_t __hibits = (size_t)__val; | |
51 | __val = (__val - (long double)__hibits) * __mult; | |
52 | ||
53 | const size_t __coeff = __SIZE_MAX__ / __LDBL_MAX_EXP__; | |
54 | ||
55 | return __hibits + (size_t)__val + __coeff * __exponent; | |
56 | } | |
57 | } | |
58 | } |