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1 | // std::__detail definitions -*- C++ -*- | |
2 | ||
3 | // Copyright (C) 2007-2020 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 "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 | if (__n == 0) | |
55 | // Special case on container 1st initialization with 0 bucket count | |
56 | // hint. We keep _M_next_resize to 0 to make sure that next time we | |
57 | // want to add an element allocation will take place. | |
58 | return 1; | |
59 | ||
60 | _M_next_resize = | |
61 | __builtin_floorl(__fast_bkt[__n] * (long double)_M_max_load_factor); | |
62 | return __fast_bkt[__n]; | |
63 | } | |
64 | ||
65 | // Number of primes (without sentinel). | |
66 | constexpr auto __n_primes | |
67 | = sizeof(__prime_list) / sizeof(unsigned long) - 1; | |
68 | ||
69 | // Don't include the last prime in the search, so that anything | |
70 | // higher than the second-to-last prime returns a past-the-end | |
71 | // iterator that can be dereferenced to get the last prime. | |
72 | constexpr auto __last_prime = __prime_list + __n_primes - 1; | |
73 | ||
74 | const unsigned long* __next_bkt = | |
75 | std::lower_bound(__prime_list + 6, __last_prime, __n); | |
76 | ||
77 | if (__next_bkt == __last_prime) | |
78 | // Set next resize to the max value so that we never try to rehash again | |
79 | // as we already reach the biggest possible bucket number. | |
80 | // Note that it might result in max_load_factor not being respected. | |
81 | _M_next_resize = numeric_limits<size_t>::max(); | |
82 | else | |
83 | _M_next_resize = | |
84 | __builtin_floorl(*__next_bkt * (long double)_M_max_load_factor); | |
85 | ||
86 | return *__next_bkt; | |
87 | } | |
88 | ||
89 | // Finds the smallest prime p such that alpha p > __n_elt + __n_ins. | |
90 | // If p > __n_bkt, return make_pair(true, p); otherwise return | |
91 | // make_pair(false, 0). In principle this isn't very different from | |
92 | // _M_bkt_for_elements. | |
93 | ||
94 | // The only tricky part is that we're caching the element count at | |
95 | // which we need to rehash, so we don't have to do a floating-point | |
96 | // multiply for every insertion. | |
97 | ||
98 | std::pair<bool, std::size_t> | |
99 | _Prime_rehash_policy:: | |
100 | _M_need_rehash(std::size_t __n_bkt, std::size_t __n_elt, | |
101 | std::size_t __n_ins) const | |
102 | { | |
103 | if (__n_elt + __n_ins > _M_next_resize) | |
104 | { | |
105 | // If _M_next_resize is 0 it means that we have nothing allocated so | |
106 | // far and that we start inserting elements. In this case we start | |
107 | // with an initial bucket size of 11. | |
108 | long double __min_bkts | |
109 | = std::max<std::size_t>(__n_elt + __n_ins, _M_next_resize ? 0 : 11) | |
110 | / (long double)_M_max_load_factor; | |
111 | if (__min_bkts >= __n_bkt) | |
112 | return { true, | |
113 | _M_next_bkt(std::max<std::size_t>(__builtin_floorl(__min_bkts) + 1, | |
114 | __n_bkt * _S_growth_factor)) }; | |
115 | ||
116 | _M_next_resize | |
117 | = __builtin_floorl(__n_bkt * (long double)_M_max_load_factor); | |
118 | return { false, 0 }; | |
119 | } | |
120 | else | |
121 | return { false, 0 }; | |
122 | } | |
123 | } // namespace __detail | |
124 | ||
125 | _GLIBCXX_END_NAMESPACE_VERSION | |
126 | } // namespace std |