libstdc++-v3/src/c++11/hashtable_c++0x.cc

   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[]
  50       = { 2, 2, 2, 3, 5, 5, 7, 7, 11, 11, 11, 11, 13, 13 };
  51
  52     if (__n < sizeof(__fast_bkt))
  53       {
  54         _M_next_resize =
  55           __builtin_floor(__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     const unsigned long* __next_bkt =
  69       std::lower_bound(__prime_list + 6, __last_prime, __n);
  70
  71     if (__next_bkt == __last_prime)
  72       // Set next resize to the max value so that we never try to rehash again
  73       // as we already reach the biggest possible bucket number.
  74       // Note that it might result in max_load_factor not being respected.
  75       _M_next_resize = std::size_t(-1);
  76     else
  77       _M_next_resize =
  78         __builtin_floor(*__next_bkt * (long double)_M_max_load_factor);
  79
  80     return *__next_bkt;
  81   }
  82
  83   // Finds the smallest prime p such that alpha p > __n_elt + __n_ins.
  84   // If p > __n_bkt, return make_pair(true, p); otherwise return
  85   // make_pair(false, 0).  In principle this isn't very different from
  86   // _M_bkt_for_elements.
  87
  88   // The only tricky part is that we're caching the element count at
  89   // which we need to rehash, so we don't have to do a floating-point
  90   // multiply for every insertion.
  91
  92   std::pair<bool, std::size_t>
  93   _Prime_rehash_policy::
  94   _M_need_rehash(std::size_t __n_bkt, std::size_t __n_elt,
  95                  std::size_t __n_ins) const
  96   {
  97     if (__n_elt + __n_ins > _M_next_resize)
  98       {
  99         long double __min_bkts = (__n_elt + __n_ins)
 100                                    / (long double)_M_max_load_factor;
 101         if (__min_bkts >= __n_bkt)
 102           return std::make_pair(true,
 103             _M_next_bkt(std::max<std::size_t>(__builtin_floor(__min_bkts) + 1,
 104                                               __n_bkt * _S_growth_factor)));
 105
 106         _M_next_resize
 107           = __builtin_floor(__n_bkt * (long double)_M_max_load_factor);
 108         return std::make_pair(false, 0);
 109       }
 110     else
 111       return std::make_pair(false, 0);
 112   }
 113 } // namespace __detail
 114
 115 _GLIBCXX_END_NAMESPACE_VERSION
 116 } // namespace std