incentive/psopeeps-newserv
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

make PRS compression faster & more efficient

Browse Source
This commit is contained in:
Martin Michelsen
2023-01-17 22:02:24 -08:00
parent a937e50681
commit 133ca0b3cc
2 changed files with 23 additions and 14 deletions
Download Patch File Download Diff File Expand all files Collapse all files
src/Compression.cc
+22 -14
View File
@@ -20,7 +20,8 @@ PRSCompressor::PRSCompressor(function<void(size_t, size_t)> progress_fn)
control_byte_offset(0),
pending_control_bits(0),
input_bytes(0),
compression_offset(0) {
compression_offset(0),
reverse_log_offsets(0x100) {
this->output.put_u8(0);
}
@@ -51,11 +52,12 @@ void PRSCompressor::advance() {
// Search for a match in the decompressed data history
size_t best_match_size = 0;
size_t best_match_offset = 0;
size_t start_offset = max<ssize_t>(
0, static_cast<ssize_t>(this->compression_offset) - 0x1FFF);
for (size_t match_offset = start_offset;
(match_offset < this->compression_offset - best_match_size) && (best_match_size < 0x100);
match_offset++) {
uint8_t first_v = this->forward_log[this->compression_offset & 0xFF];
const auto& start_offsets = this->reverse_log_offsets[first_v];
for (auto it = start_offsets.begin(); (it != start_offsets.end()) && (best_match_size < 0x100); it++) {
size_t match_offset = *it;
size_t match_size = 0;
while ((match_size < 0x100) &&
(match_offset + match_size < this->compression_offset) &&
@@ -73,20 +75,20 @@ void PRSCompressor::advance() {
// If there is a suitable match, write a backreference
bool should_write_literal = false;
size_t advance_bytes = 0;
if (best_match_size < 2) {
ssize_t backreference_offset = best_match_offset - this->compression_offset;
if (best_match_size < 2 || backreference_offset == -0x2000) {
should_write_literal = true;
} else {
// The backreference should be encoded:
// - As a short copy if offset in [-0x100, -1] and size in [2, 5]
// - As a long copy if offset in [-0x1FFF, -1] and size in [3, 9]
// - As an extended copy if offset in [-0x1FFF, -1] and size in [1, 0x100]
// Because an extended copy costs two control bits and three data bytes,
// it's not worth it to use an extended copy for sizes 1 and 2 (and 3, but
// that case is always done via a long copy instead). In cases 1 and 2, if a
// short copy can't reach back far enough, we just write literal(s) instead.
// - As an extended copy if offset in [-0x1FFF, -1] and size in [10, 0x100]
// Technically an extended copy can be used for sizes 1-9 as well, but if
// size is 1 or 2, writing literals is better (since it uses fewer data
// bytes and control bits), and a long copy can cover sizes 3-9 (and also
// uses fewer data bytes and control bits).
ssize_t backreference_offset = best_match_offset - this->compression_offset;
if ((backreference_offset >= -0x100) && (best_match_size <= 5)) {
// Write short copy
uint8_t size = best_match_size - 2;
@@ -136,7 +138,13 @@ void PRSCompressor::advance() {
if ((this->compression_offset & 0x1000) && this->progress_fn) {
this->progress_fn(this->compression_offset, this->output.size());
}
this->reverse_log[this->compression_offset & 0x1FFF] = this->forward_log[this->compression_offset & 0xFF];
size_t reverse_log_offset = this->compression_offset & 0x1FFF;
uint8_t existing_v = this->reverse_log[reverse_log_offset];
uint8_t new_v = this->forward_log[this->compression_offset & 0xFF];
this->reverse_log_offsets[existing_v].erase(this->compression_offset - this->reverse_log.size());
this->reverse_log[reverse_log_offset] = new_v;
this->reverse_log_offsets[new_v].emplace(this->compression_offset);
this->compression_offset++;
}
}