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117 lines
4.1 KiB
C++
117 lines
4.1 KiB
C++
/* Copyright 2013 Google Inc. All Rights Reserved.
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Distributed under MIT license.
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See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
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*/
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// Function to find backward reference copies.
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#ifndef BROTLI_ENC_BACKWARD_REFERENCES_H_
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#define BROTLI_ENC_BACKWARD_REFERENCES_H_
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#include <vector>
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#include "./hash.h"
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#include "./command.h"
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#include "./types.h"
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namespace brotli {
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// "commands" points to the next output command to write to, "*num_commands" is
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// initially the total amount of commands output by previous
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// CreateBackwardReferences calls, and must be incremented by the amount written
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// by this call.
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void CreateBackwardReferences(size_t num_bytes,
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size_t position,
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bool is_last,
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const uint8_t* ringbuffer,
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size_t ringbuffer_mask,
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const int quality,
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const int lgwin,
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Hashers* hashers,
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int hash_type,
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int* dist_cache,
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size_t* last_insert_len,
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Command* commands,
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size_t* num_commands,
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size_t* num_literals);
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static const float kInfinity = std::numeric_limits<float>::infinity();
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struct ZopfliNode {
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ZopfliNode(void) : length(1),
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distance(0),
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insert_length(0),
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cost(kInfinity) {}
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inline uint32_t copy_length() const {
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return length & 0xffffff;
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}
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inline uint32_t length_code() const {
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const uint32_t modifier = length >> 24;
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return copy_length() + 9u - modifier;
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}
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inline uint32_t copy_distance() const {
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return distance & 0x1ffffff;
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}
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inline uint32_t distance_code() const {
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const uint32_t short_code = distance >> 25;
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return short_code == 0 ? copy_distance() + 15 : short_code - 1;
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}
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inline uint32_t command_length() const {
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return copy_length() + insert_length;
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}
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// best length to get up to this byte (not including this byte itself)
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// highest 8 bit is used to reconstruct the length code
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uint32_t length;
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// distance associated with the length
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// highest 7 bit contains distance short code + 1 (or zero if no short code)
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uint32_t distance;
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// number of literal inserts before this copy
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uint32_t insert_length;
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// smallest cost to get to this byte from the beginning, as found so far
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float cost;
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};
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// Computes the shortest path of commands from position to at most
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// position + num_bytes.
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//
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// On return, path->size() is the number of commands found and path[i] is the
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// length of the ith command (copy length plus insert length).
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// Note that the sum of the lengths of all commands can be less than num_bytes.
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//
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// On return, the nodes[0..num_bytes] array will have the following
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// "ZopfliNode array invariant":
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// For each i in [1..num_bytes], if nodes[i].cost < kInfinity, then
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// (1) nodes[i].copy_length() >= 2
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// (2) nodes[i].command_length() <= i and
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// (3) nodes[i - nodes[i].command_length()].cost < kInfinity
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void ZopfliComputeShortestPath(size_t num_bytes,
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size_t position,
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const uint8_t* ringbuffer,
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size_t ringbuffer_mask,
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const size_t max_backward_limit,
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const int* dist_cache,
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Hashers::H10* hasher,
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ZopfliNode* nodes,
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std::vector<uint32_t>* path);
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void ZopfliCreateCommands(const size_t num_bytes,
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const size_t block_start,
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const size_t max_backward_limit,
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const std::vector<uint32_t>& path,
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const ZopfliNode* nodes,
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int* dist_cache,
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size_t* last_insert_len,
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Command* commands,
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size_t* num_literals);
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} // namespace brotli
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#endif // BROTLI_ENC_BACKWARD_REFERENCES_H_
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