1 // std::tr1::hash definitions, long double bits -*- C++ -*- 2 3 // Copyright (C) 2010, 2011 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 namespace 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