1 // std::__detail definitions -*- C++ -*- 2 3 // Copyright (C) 2007-2018 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 "hashtable_c++0x.cc must be compiled with -std=gnu++0x" 27 #endif 28 29 #include <initializer_list> 30 #include <tuple> 31 #include <ext/aligned_buffer.h> 32 #include <ext/alloc_traits.h> 33 #include <bits/hashtable_policy.h> 34 35 namespace std _GLIBCXX_VISIBILITY(default) 36 { 37 _GLIBCXX_BEGIN_NAMESPACE_VERSION 38 39 #include "../shared/hashtable-aux.cc" 40 41 namespace __detail 42 { 43 // Return a prime no smaller than n. 44 std::size_t 45 _Prime_rehash_policy::_M_next_bkt(std::size_t __n) const 46 { 47 // Optimize lookups involving the first elements of __prime_list. 48 // (useful to speed-up, eg, constructors) 49 static const unsigned char __fast_bkt[13] 50 = { 2, 2, 3, 5, 5, 7, 7, 11, 11, 11, 11, 13, 13 }; 51 52 if (__n <= 12) 53 { 54 _M_next_resize = 55 __builtin_ceil(__fast_bkt[__n] * (long double)_M_max_load_factor); 56 return __fast_bkt[__n]; 57 } 58 59 // Number of primes (without sentinel). 60 constexpr auto __n_primes 61 = sizeof(__prime_list) / sizeof(unsigned long) - 1; 62 63 // Don't include the last prime in the search, so that anything 64 // higher than the second-to-last prime returns a past-the-end 65 // iterator that can be dereferenced to get the last prime. 66 constexpr auto __last_prime = __prime_list + __n_primes - 1; 67 68 // Look for 'n + 1' to make sure returned value will be greater than n. 69 const unsigned long* __next_bkt = 70 std::lower_bound(__prime_list + 6, __last_prime, __n + 1); 71 72 if (__next_bkt == __last_prime) 73 // Set next resize to the max value so that we never try to rehash again 74 // as we already reach the biggest possible bucket number. 75 // Note that it might result in max_load_factor not being respected. 76 _M_next_resize = std::size_t(-1); 77 else 78 _M_next_resize = 79 __builtin_ceil(*__next_bkt * (long double)_M_max_load_factor); 80 81 return *__next_bkt; 82 } 83 84 // Finds the smallest prime p such that alpha p > __n_elt + __n_ins. 85 // If p > __n_bkt, return make_pair(true, p); otherwise return 86 // make_pair(false, 0). In principle this isn't very different from 87 // _M_bkt_for_elements. 88 89 // The only tricky part is that we're caching the element count at 90 // which we need to rehash, so we don't have to do a floating-point 91 // multiply for every insertion. 92 93 std::pair<bool, std::size_t> 94 _Prime_rehash_policy:: 95 _M_need_rehash(std::size_t __n_bkt, std::size_t __n_elt, 96 std::size_t __n_ins) const 97 { 98 if (__n_elt + __n_ins >= _M_next_resize) 99 { 100 long double __min_bkts = (__n_elt + __n_ins) 101 / (long double)_M_max_load_factor; 102 if (__min_bkts >= __n_bkt) 103 return std::make_pair(true, 104 _M_next_bkt(std::max<std::size_t>(__builtin_floor(__min_bkts) + 1, 105 __n_bkt * _S_growth_factor))); 106 107 _M_next_resize 108 = __builtin_floor(__n_bkt * (long double)_M_max_load_factor); 109 return std::make_pair(false, 0); 110 } 111 else 112 return std::make_pair(false, 0); 113 } 114 } // namespace __detail 115 116 _GLIBCXX_END_NAMESPACE_VERSION 117 } // namespace std 118