libstdc++
hash_prime_size_policy_imp.hpp
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1 // -*- C++ -*-
2 
3 // Copyright (C) 2005-2020 Free Software Foundation, Inc.
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25 // Copyright (C) 2004 Ami Tavory and Vladimir Dreizin, IBM-HRL.
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35 
36 /**
37  * @file hash_prime_size_policy_imp.hpp
38  * Contains a resize size policy implementation.
39  */
40 
41 #ifdef PB_DS_CLASS_C_DEC
42 
43 #pragma GCC system_header
44 
45 namespace detail
46 {
47  enum
48  {
49  num_distinct_sizes_32_bit = 30,
50  num_distinct_sizes_64_bit = 62,
51  num_distinct_sizes = sizeof(std::size_t) != 8 ?
52  num_distinct_sizes_32_bit : num_distinct_sizes_64_bit,
53  };
54 
55  // Originally taken from the SGI implementation; acknowledged in the docs.
56  // Further modified (for 64 bits) from tr1's hashtable.
57  static const std::size_t g_a_sizes[num_distinct_sizes_64_bit] =
58  {
59  /* 0 */ 5ul,
60  /* 1 */ 11ul,
61  /* 2 */ 23ul,
62  /* 3 */ 47ul,
63  /* 4 */ 97ul,
64  /* 5 */ 199ul,
65  /* 6 */ 409ul,
66  /* 7 */ 823ul,
67  /* 8 */ 1741ul,
68  /* 9 */ 3469ul,
69  /* 10 */ 6949ul,
70  /* 11 */ 14033ul,
71  /* 12 */ 28411ul,
72  /* 13 */ 57557ul,
73  /* 14 */ 116731ul,
74  /* 15 */ 236897ul,
75  /* 16 */ 480881ul,
76  /* 17 */ 976369ul,
77  /* 18 */ 1982627ul,
78  /* 19 */ 4026031ul,
79  /* 20 */ 8175383ul,
80  /* 21 */ 16601593ul,
81  /* 22 */ 33712729ul,
82  /* 23 */ 68460391ul,
83  /* 24 */ 139022417ul,
84  /* 25 */ 282312799ul,
85  /* 26 */ 573292817ul,
86  /* 27 */ 1164186217ul,
87  /* 28 */ 2364114217ul,
88  /* 29 */ 4294967291ul,
89  /* 30 */ (std::size_t)8589934583ull,
90  /* 31 */ (std::size_t)17179869143ull,
91  /* 32 */ (std::size_t)34359738337ull,
92  /* 33 */ (std::size_t)68719476731ull,
93  /* 34 */ (std::size_t)137438953447ull,
94  /* 35 */ (std::size_t)274877906899ull,
95  /* 36 */ (std::size_t)549755813881ull,
96  /* 37 */ (std::size_t)1099511627689ull,
97  /* 38 */ (std::size_t)2199023255531ull,
98  /* 39 */ (std::size_t)4398046511093ull,
99  /* 40 */ (std::size_t)8796093022151ull,
100  /* 41 */ (std::size_t)17592186044399ull,
101  /* 42 */ (std::size_t)35184372088777ull,
102  /* 43 */ (std::size_t)70368744177643ull,
103  /* 44 */ (std::size_t)140737488355213ull,
104  /* 45 */ (std::size_t)281474976710597ull,
105  /* 46 */ (std::size_t)562949953421231ull,
106  /* 47 */ (std::size_t)1125899906842597ull,
107  /* 48 */ (std::size_t)2251799813685119ull,
108  /* 49 */ (std::size_t)4503599627370449ull,
109  /* 50 */ (std::size_t)9007199254740881ull,
110  /* 51 */ (std::size_t)18014398509481951ull,
111  /* 52 */ (std::size_t)36028797018963913ull,
112  /* 53 */ (std::size_t)72057594037927931ull,
113  /* 54 */ (std::size_t)144115188075855859ull,
114  /* 55 */ (std::size_t)288230376151711717ull,
115  /* 56 */ (std::size_t)576460752303423433ull,
116  /* 57 */ (std::size_t)1152921504606846883ull,
117  /* 58 */ (std::size_t)2305843009213693951ull,
118  /* 59 */ (std::size_t)4611686018427387847ull,
119  /* 60 */ (std::size_t)9223372036854775783ull,
120  /* 61 */ (std::size_t)18446744073709551557ull,
121  };
122 
123 } // namespace detail
124 
125 PB_DS_CLASS_T_DEC
126 inline
127 PB_DS_CLASS_C_DEC::
128 hash_prime_size_policy(size_type n) : m_start_size(n)
129 { m_start_size = get_nearest_larger_size(n); }
130 
131 PB_DS_CLASS_T_DEC
132 inline void
133 PB_DS_CLASS_C_DEC::
134 swap(PB_DS_CLASS_C_DEC& other)
135 { std::swap(m_start_size, other.m_start_size); }
136 
137 PB_DS_CLASS_T_DEC
138 inline PB_DS_CLASS_C_DEC::size_type
139 PB_DS_CLASS_C_DEC::
140 get_nearest_larger_size(size_type n) const
141 {
142  const std::size_t* const p_upper = std::upper_bound(detail::g_a_sizes,
143  detail::g_a_sizes + detail::num_distinct_sizes, n);
144 
145  if (p_upper == detail::g_a_sizes + detail::num_distinct_sizes)
146  __throw_resize_error();
147  return *p_upper;
148 }
149 
150 PB_DS_CLASS_T_DEC
151 inline PB_DS_CLASS_C_DEC::size_type
152 PB_DS_CLASS_C_DEC::
153 get_nearest_smaller_size(size_type n) const
154 {
155  const std::size_t* p_lower = std::lower_bound(detail::g_a_sizes,
156  detail::g_a_sizes + detail::num_distinct_sizes, n);
157 
158  if (*p_lower >= n && p_lower != detail::g_a_sizes)
159  --p_lower;
160  if (*p_lower < m_start_size)
161  return m_start_size;
162  return *p_lower;
163 }
164 #endif