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Improved PRS compression performance.

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This commit is contained in:
Daan Vanden Bosch 2020-07-19 00:13:49 +02:00
parent 8b8e87c8c5
commit 6fd94c1de2
2 changed files with 10 additions and 26 deletions
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6
src/core/data_formats/block/cursor/BufferCursor.ts
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@ -22,13 +22,13 @@ export class BufferCursor extends AbstractArrayBufferCursor {
buffer: Buffer,
endianness: Endianness,
offset: number = 0,
size: number = buffer.byteLength - offset,
size: number = buffer.length - offset,
) {
if (offset < 0 || offset > buffer.byteLength) {
if (offset < 0 || offset > buffer.length) {
throw new Error(`Offset ${offset} is out of bounds.`);
}
if (size < 0 || size > buffer.byteLength - offset) {
if (size < 0 || size > buffer.length - offset) {
throw new Error(`Size ${size} is out of bounds.`);
}

30
src/core/data_formats/compression/prs/compress.ts
View File

@ -21,38 +21,22 @@ export function prs_compress(cursor: Cursor): Cursor {
export function prs_compress_js(cursor: Cursor): Cursor {
const pc = new Context(cursor.size, cursor.endianness);
const comp_cursor = cursor.take(cursor.size);
cursor.seek_start(0);
while (cursor.bytes_left) {
// Find the longest match.
let best_offset = 0;
let best_size = 0;
const min_offset = Math.max(0, cursor.position - Math.min(0x800, cursor.bytes_left));
const start_pos = cursor.position;
const min_offset = Math.max(0, start_pos - Math.min(0x800, cursor.bytes_left));
for (let i = cursor.position - 255; i >= min_offset; i--) {
const start_pos = cursor.position;
let s1 = start_pos;
let s2 = i;
for (let i = start_pos - 255; i >= min_offset; i--) {
comp_cursor.seek_start(i);
let size = 0;
// Optimization: compare 4 bytes at a time while we can.
while (
s1 + 3 < cursor.size &&
size < 252 &&
cursor.seek_start(s1).u32() === cursor.seek_start(s2).u32()
) {
size += 4;
s1 += 4;
s2 += 4;
}
while (
s1 < cursor.size &&
size < 255 &&
cursor.seek_start(s1).u8() === cursor.seek_start(s2).u8()
) {
while (cursor.bytes_left && size <= 254 && cursor.u8() === comp_cursor.u8()) {
size++;
s1++;
s2++;
}
cursor.seek_start(start_pos);