1 |
424 |
jeremybenn |
// std::hash and std::tr1::hash definitions, long double bits -*- C++ -*-
|
2 |
|
|
|
3 |
|
|
// Copyright (C) 2010 Free Software Foundation, Inc.
|
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 |
|
|
|
25 |
|
|
// For long double, careful with random padding bits (e.g., on x86,
|
26 |
|
|
// 10 bytes -> 12 bytes) and resort to frexp.
|
27 |
|
|
template<>
|
28 |
|
|
size_t
|
29 |
|
|
hash<long double>::operator()(long double __val) const
|
30 |
|
|
{
|
31 |
|
|
// 0 and -0 both hash to zero.
|
32 |
|
|
if (__val == 0.0L)
|
33 |
|
|
return 0;
|
34 |
|
|
|
35 |
|
|
int __exponent;
|
36 |
|
|
__val = __builtin_frexpl(__val, &__exponent);
|
37 |
|
|
__val = __val < 0.0l ? -(__val + 0.5l) : __val;
|
38 |
|
|
|
39 |
|
|
const long double __mult = __SIZE_MAX__ + 1.0l;
|
40 |
|
|
__val *= __mult;
|
41 |
|
|
|
42 |
|
|
// Try to use all the bits of the mantissa (really necessary only
|
43 |
|
|
// on 32-bit targets, at least for 80-bit floating point formats).
|
44 |
|
|
const size_t __hibits = (size_t)__val;
|
45 |
|
|
__val = (__val - (long double)__hibits) * __mult;
|
46 |
|
|
|
47 |
|
|
const size_t __coeff = __SIZE_MAX__ / __LDBL_MAX_EXP__;
|
48 |
|
|
|
49 |
|
|
return __hibits + (size_t)__val + __coeff * __exponent;
|
50 |
|
|
}
|