1// std::tr1::hash definitions, long double bits -*- C++ -*-
2
3// Copyright (C) 2010-2020 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#pragma GCC diagnostic ignored "-Wattribute-alias"
26
27namespace std _GLIBCXX_VISIBILITY(default)
28{
29  namespace tr1
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}
59