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