[857] | 1 | // Copyright (C) 2000, 2001 Stephen Cleary
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| 2 | //
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| 3 | // Distributed under the Boost Software License, Version 1.0. (See
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| 4 | // accompanying file LICENSE_1_0.txt or copy at
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| 5 | // http://www.boost.org/LICENSE_1_0.txt)
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| 6 | //
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| 7 | // See http://www.boost.org for updates, documentation, and revision history.
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| 8 |
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| 9 | #ifndef BOOST_SIMPLE_SEGREGATED_STORAGE_HPP
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| 10 | #define BOOST_SIMPLE_SEGREGATED_STORAGE_HPP
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| 11 |
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| 12 | // std::greater
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| 13 | #include <functional>
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| 14 |
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| 15 | #include <boost/pool/poolfwd.hpp>
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| 16 |
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| 17 | namespace boost {
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| 18 |
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| 19 | template <typename SizeType>
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| 20 | class simple_segregated_storage
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| 21 | {
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| 22 | public:
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| 23 | typedef SizeType size_type;
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| 24 |
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| 25 | private:
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| 26 | simple_segregated_storage(const simple_segregated_storage &);
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| 27 | void operator=(const simple_segregated_storage &);
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| 28 |
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| 29 | // pre: (n > 0), (start != 0), (nextof(start) != 0)
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| 30 | // post: (start != 0)
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| 31 | static void * try_malloc_n(void * & start, size_type n,
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| 32 | size_type partition_size);
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| 33 |
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| 34 | protected:
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| 35 | void * first;
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| 36 |
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| 37 | // Traverses the free list referred to by "first",
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| 38 | // and returns the iterator previous to where
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| 39 | // "ptr" would go if it was in the free list.
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| 40 | // Returns 0 if "ptr" would go at the beginning
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| 41 | // of the free list (i.e., before "first")
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| 42 | void * find_prev(void * ptr);
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| 43 |
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| 44 | // for the sake of code readability :)
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| 45 | static void * & nextof(void * const ptr)
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| 46 | { return *(static_cast<void **>(ptr)); }
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| 47 |
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| 48 | public:
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| 49 | // Post: empty()
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| 50 | simple_segregated_storage()
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| 51 | :first(0) { }
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| 52 |
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| 53 | // pre: npartition_sz >= sizeof(void *)
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| 54 | // npartition_sz = sizeof(void *) * i, for some integer i
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| 55 | // nsz >= npartition_sz
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| 56 | // block is properly aligned for an array of object of
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| 57 | // size npartition_sz and array of void *
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| 58 | // The requirements above guarantee that any pointer to a chunk
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| 59 | // (which is a pointer to an element in an array of npartition_sz)
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| 60 | // may be cast to void **.
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| 61 | static void * segregate(void * block,
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| 62 | size_type nsz, size_type npartition_sz,
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| 63 | void * end = 0);
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| 64 |
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| 65 | // Same preconditions as 'segregate'
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| 66 | // Post: !empty()
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| 67 | void add_block(void * const block,
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| 68 | const size_type nsz, const size_type npartition_sz)
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| 69 | {
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| 70 | // Segregate this block and merge its free list into the
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| 71 | // free list referred to by "first"
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| 72 | first = segregate(block, nsz, npartition_sz, first);
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| 73 | }
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| 74 |
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| 75 | // Same preconditions as 'segregate'
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| 76 | // Post: !empty()
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| 77 | void add_ordered_block(void * const block,
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| 78 | const size_type nsz, const size_type npartition_sz)
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| 79 | {
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| 80 | // This (slower) version of add_block segregates the
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| 81 | // block and merges its free list into our free list
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| 82 | // in the proper order
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| 83 |
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| 84 | // Find where "block" would go in the free list
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| 85 | void * const loc = find_prev(block);
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| 86 |
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| 87 | // Place either at beginning or in middle/end
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| 88 | if (loc == 0)
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| 89 | add_block(block, nsz, npartition_sz);
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| 90 | else
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| 91 | nextof(loc) = segregate(block, nsz, npartition_sz, nextof(loc));
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| 92 | }
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| 93 |
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| 94 | // default destructor
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| 95 |
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| 96 | bool empty() const { return (first == 0); }
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| 97 |
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| 98 | // pre: !empty()
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| 99 | void * malloc()
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| 100 | {
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| 101 | void * const ret = first;
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| 102 |
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| 103 | // Increment the "first" pointer to point to the next chunk
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| 104 | first = nextof(first);
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| 105 | return ret;
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| 106 | }
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| 107 |
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| 108 | // pre: chunk was previously returned from a malloc() referring to the
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| 109 | // same free list
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| 110 | // post: !empty()
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| 111 | void free(void * const chunk)
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| 112 | {
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| 113 | nextof(chunk) = first;
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| 114 | first = chunk;
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| 115 | }
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| 116 |
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| 117 | // pre: chunk was previously returned from a malloc() referring to the
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| 118 | // same free list
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| 119 | // post: !empty()
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| 120 | void ordered_free(void * const chunk)
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| 121 | {
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| 122 | // This (slower) implementation of 'free' places the memory
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| 123 | // back in the list in its proper order.
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| 124 |
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| 125 | // Find where "chunk" goes in the free list
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| 126 | void * const loc = find_prev(chunk);
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| 127 |
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| 128 | // Place either at beginning or in middle/end
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| 129 | if (loc == 0)
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| 130 | free(chunk);
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| 131 | else
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| 132 | {
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| 133 | nextof(chunk) = nextof(loc);
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| 134 | nextof(loc) = chunk;
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| 135 | }
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| 136 | }
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| 137 |
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| 138 | // Note: if you're allocating/deallocating n a lot, you should
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| 139 | // be using an ordered pool.
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| 140 | void * malloc_n(size_type n, size_type partition_size);
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| 141 |
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| 142 | // pre: chunks was previously allocated from *this with the same
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| 143 | // values for n and partition_size
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| 144 | // post: !empty()
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| 145 | // Note: if you're allocating/deallocating n a lot, you should
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| 146 | // be using an ordered pool.
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| 147 | void free_n(void * const chunks, const size_type n,
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| 148 | const size_type partition_size)
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| 149 | {
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| 150 | add_block(chunks, n * partition_size, partition_size);
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| 151 | }
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| 152 |
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| 153 | // pre: chunks was previously allocated from *this with the same
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| 154 | // values for n and partition_size
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| 155 | // post: !empty()
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| 156 | void ordered_free_n(void * const chunks, const size_type n,
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| 157 | const size_type partition_size)
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| 158 | {
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| 159 | add_ordered_block(chunks, n * partition_size, partition_size);
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| 160 | }
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| 161 | };
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| 162 |
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| 163 | template <typename SizeType>
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| 164 | void * simple_segregated_storage<SizeType>::find_prev(void * const ptr)
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| 165 | {
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| 166 | // Handle border case
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| 167 | if (first == 0 || std::greater<void *>()(first, ptr))
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| 168 | return 0;
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| 169 |
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| 170 | void * iter = first;
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| 171 | while (true)
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| 172 | {
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| 173 | // if we're about to hit the end or
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| 174 | // if we've found where "ptr" goes
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| 175 | if (nextof(iter) == 0 || std::greater<void *>()(nextof(iter), ptr))
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| 176 | return iter;
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| 177 |
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| 178 | iter = nextof(iter);
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| 179 | }
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| 180 | }
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| 181 |
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| 182 | template <typename SizeType>
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| 183 | void * simple_segregated_storage<SizeType>::segregate(
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| 184 | void * const block,
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| 185 | const size_type sz,
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| 186 | const size_type partition_sz,
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| 187 | void * const end)
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| 188 | {
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| 189 | // Get pointer to last valid chunk, preventing overflow on size calculations
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| 190 | // The division followed by the multiplication just makes sure that
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| 191 | // old == block + partition_sz * i, for some integer i, even if the
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| 192 | // block size (sz) is not a multiple of the partition size.
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| 193 | char * old = static_cast<char *>(block)
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| 194 | + ((sz - partition_sz) / partition_sz) * partition_sz;
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| 195 |
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| 196 | // Set it to point to the end
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| 197 | nextof(old) = end;
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| 198 |
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| 199 | // Handle border case where sz == partition_sz (i.e., we're handling an array
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| 200 | // of 1 element)
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| 201 | if (old == block)
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| 202 | return block;
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| 203 |
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| 204 | // Iterate backwards, building a singly-linked list of pointers
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| 205 | for (char * iter = old - partition_sz; iter != block;
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| 206 | old = iter, iter -= partition_sz)
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| 207 | nextof(iter) = old;
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| 208 |
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| 209 | // Point the first pointer, too
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| 210 | nextof(block) = old;
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| 211 |
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| 212 | return block;
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| 213 | }
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| 214 |
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| 215 | // The following function attempts to find n contiguous chunks
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| 216 | // of size partition_size in the free list, starting at start.
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| 217 | // If it succeds, it returns the last chunk in that contiguous
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| 218 | // sequence, so that the sequence is known by [start, {retval}]
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| 219 | // If it fails, it does do either because it's at the end of the
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| 220 | // free list or hits a non-contiguous chunk. In either case,
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| 221 | // it will return 0, and set start to the last considered
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| 222 | // chunk. You are at the end of the free list if
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| 223 | // nextof(start) == 0. Otherwise, start points to the last
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| 224 | // chunk in the contiguous sequence, and nextof(start) points
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| 225 | // to the first chunk in the next contiguous sequence (assuming
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| 226 | // an ordered free list)
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| 227 | template <typename SizeType>
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| 228 | void * simple_segregated_storage<SizeType>::try_malloc_n(
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| 229 | void * & start, size_type n, const size_type partition_size)
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| 230 | {
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| 231 | void * iter = nextof(start);
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| 232 | while (--n != 0)
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| 233 | {
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| 234 | void * next = nextof(iter);
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| 235 | if (next != static_cast<char *>(iter) + partition_size)
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| 236 | {
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| 237 | // next == 0 (end-of-list) or non-contiguous chunk found
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| 238 | start = iter;
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| 239 | return 0;
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| 240 | }
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| 241 | iter = next;
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| 242 | }
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| 243 | return iter;
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| 244 | }
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| 245 |
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| 246 | template <typename SizeType>
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| 247 | void * simple_segregated_storage<SizeType>::malloc_n(const size_type n,
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| 248 | const size_type partition_size)
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| 249 | {
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| 250 | void * start = &first;
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| 251 | void * iter;
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| 252 | do
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| 253 | {
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| 254 | if (nextof(start) == 0)
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| 255 | return 0;
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| 256 | iter = try_malloc_n(start, n, partition_size);
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| 257 | } while (iter == 0);
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| 258 | void * const ret = nextof(start);
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| 259 | nextof(start) = nextof(iter);
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| 260 | return ret;
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| 261 | }
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| 262 |
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| 263 | } // namespace boost
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| 264 |
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| 265 | #endif
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