1 // std::hash definitions -*- 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 #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 32 namespace std _GLIBCXX_VISIBILITY(default) 33 { 34 _GLIBCXX_PURE size_t operator ()(long double __val) const35 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