1// std::tr1::hash definitions, long double bits -*- C++ -*-
2
3// Copyright (C) 2010-2015 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
25namespace std _GLIBCXX_VISIBILITY(default)
26{
27  namespace tr1
28  {
29    // For long double, careful with random padding bits (e.g., on x86,
30    // 10 bytes -> 12 bytes) and resort to frexp.
31    template<>
32      size_t
33      hash<long double>::operator()(long double __val) const
34      {
35	// 0 and -0 both hash to zero.
36	if (__val == 0.0L)
37	  return 0;
38
39	int __exponent;
40	__val = __builtin_frexpl(__val, &__exponent);
41	__val = __val < 0.0l ? -(__val + 0.5l) : __val;
42
43	const long double __mult = __SIZE_MAX__ + 1.0l;
44	__val *= __mult;
45
46	// Try to use all the bits of the mantissa (really necessary only
47	// on 32-bit targets, at least for 80-bit floating point formats).
48	const size_t __hibits = (size_t)__val;
49	__val = (__val - (long double)__hibits) * __mult;
50
51	const size_t __coeff = __SIZE_MAX__ / __LDBL_MAX_EXP__;
52
53	return __hibits + (size_t)__val + __coeff * __exponent;
54      }
55  }
56}
57