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106 lines
3.5 KiB
C++
106 lines
3.5 KiB
C++
/*
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* This is part of HarfBuzz, a text shaping library.
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*
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* Permission is hereby granted, without written agreement and without
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* license or royalty fees, to use, copy, modify, and distribute this
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* software and its documentation for any purpose, provided that the
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* above copyright notice and the following two paragraphs appear in
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* all copies of this software.
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*
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* IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE TO ANY PARTY FOR
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* DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
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* ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN
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* IF THE COPYRIGHT HOLDER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
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* DAMAGE.
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*
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* THE COPYRIGHT HOLDER SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING,
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* BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
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* FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS
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* ON AN "AS IS" BASIS, AND THE COPYRIGHT HOLDER HAS NO OBLIGATION TO
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* PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
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*
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* Author(s): Behdad Esfahbod
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*/
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#ifndef HB_ALLOC_POOL_HH
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#define HB_ALLOC_POOL_HH
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#include "hb-vector.hh"
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/* Memory pool for persistent small- to medium-sized allocations.
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*
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* Some AI musings on this, not necessarily true:
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*
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* This is a very simple implementation, but it's good enough for our
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* purposes. It's not thread-safe. It's not very fast. It's not
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* very memory efficient. It's not very cache efficient. It's not
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* very anything efficient. But it's simple and it works. And it's
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* good enough for our purposes. If you need something more
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* sophisticated, use a real allocator. Or use a real language. */
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struct hb_alloc_pool_t
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{
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unsigned ChunkSize = 65536 - 2 * sizeof (void *);
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void *alloc (size_t size, unsigned alignment = 2 * sizeof (void *))
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{
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if (unlikely (chunks.in_error ())) return nullptr;
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assert (alignment > 0);
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assert (alignment <= 2 * sizeof (void *));
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assert ((alignment & (alignment - 1)) == 0); /* power of two */
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if (size > (ChunkSize) / 4)
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{
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/* Big chunk, allocate separately. */
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hb_vector_t<char> chunk;
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if (unlikely (!chunk.resize (size))) return nullptr;
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void *ret = chunk.arrayZ;
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chunks.push (std::move (chunk));
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if (chunks.in_error ()) return nullptr;
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if (chunks.length > 1)
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{
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// Bring back the previous last chunk to the end, so that
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// we can continue to allocate from it.
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hb_swap (chunks.arrayZ[chunks.length - 1], chunks.arrayZ[chunks.length - 2]);
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}
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return ret;
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}
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unsigned pad = (unsigned)(-(uintptr_t) current_chunk.arrayZ) & (alignment - 1);
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// Small chunk, allocate from the last chunk.
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if (current_chunk.length < pad + size)
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{
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chunks.push ();
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if (unlikely (chunks.in_error ())) return nullptr;
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hb_vector_t<char> &chunk = chunks.arrayZ[chunks.length - 1];
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if (unlikely (!chunk.resize (ChunkSize))) return nullptr;
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current_chunk = chunk;
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pad = (unsigned)(-(uintptr_t) current_chunk.arrayZ) & (alignment - 1);
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}
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current_chunk += pad;
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assert (current_chunk.length >= size);
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void *ret = current_chunk.arrayZ;
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current_chunk += size;
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return ret;
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}
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void discard (void *p_, size_t size)
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{
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// Reclaim memory if we can.
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char *p = (char *) p_;
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if (current_chunk.arrayZ == p + size && current_chunk.backwards_length >= size)
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current_chunk -= size;
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}
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private:
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hb_vector_t<hb_vector_t<char>> chunks;
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hb_array_t<char> current_chunk;
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};
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#endif /* HB_ALLOC_POOL_HH */
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