1// std::hash definitions -*- 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 25#if __cplusplus < 201103L 26# error "hash_c++0x.cc must be compiled with -std=gnu++0x" 27#endif 28 29#include <type_traits> 30#include <bits/functional_hash.h> 31 32namespace std _GLIBCXX_VISIBILITY(default) 33{ 34 _GLIBCXX_PURE size_t 35 hash<long double>::operator()(long double __val) const noexcept 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