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Improve bigrams performance (#804)

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andrews05 2026-04-01 04:57:18 +13:00 committed by GitHub
parent 5bbd826ae3
commit 7d52fd66d0
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GPG key ID: B5690EEEBB952194
1 changed files with 22 additions and 6 deletions
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28
src/png/mod.rs
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@ -1,6 +1,5 @@
use std::{fs, path::Path, sync::Arc};
use bitvec::bitarr;
use libdeflater::{CompressionLvl, Compressor};
use log::warn;
use rustc_hash::FxHashMap;
@ -373,6 +372,12 @@ impl PngImage {
let mut f_buf = Vec::new();
// For heuristic strategies, keep track of the actual filter used for each line
let mut filters_used = Vec::new();
// Pre-allocate buffers for the Bigrams strategy to avoid per-line allocations
let (mut bigram_seen, mut bigram_touched) = if matches!(strategy, FilterStrategy::Bigrams) {
(vec![false; 0x10000], Vec::<u16>::new())
} else {
(Vec::new(), Vec::new())
};
for (i, line) in self.scan_lines(false).enumerate() {
if prev_pass != line.pass || line.data.len() != prev_line.len() {
prev_line = vec![0; line.data.len()];
@ -464,18 +469,29 @@ impl PngImage {
let mut best_size = usize::MAX;
for f in try_filters {
f.filter_line(bpp, &mut line_data, &prev_line, &mut f_buf, alpha_bytes);
let mut set = bitarr![0; 0x10000];
let mut count = 0;
for pair in f_buf.windows(2) {
let bigram = ((pair[0] as usize) << 8) | pair[1] as usize;
set.set(bigram, true);
if !bigram_seen[bigram] {
count += 1;
if count >= best_size {
break;
}
bigram_seen[bigram] = true;
bigram_touched.push(bigram as u16);
}
}
let size = set.count_ones();
if size < best_size {
best_size = size;
if count < best_size {
best_size = count;
std::mem::swap(&mut best_line, &mut f_buf);
best_line_raw.clone_from(&line_data);
best_filter = *f;
}
// Clear only the entries that were touched
for &idx in &bigram_touched {
bigram_seen[idx as usize] = false;
}
bigram_touched.clear();
}
}
FilterStrategy::BigEnt => {