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[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