From 6fd94c1de2ea1377980a681b7dec6e52b0a1f8a7 Mon Sep 17 00:00:00 2001
From: Daan Vanden Bosch <daan.v.d.bosch@gmail.com>
Date: Sun, 19 Jul 2020 00:13:49 +0200
Subject: [PATCH] Improved PRS compression performance.

---
 .../data_formats/block/cursor/BufferCursor.ts |  6 ++--
 .../data_formats/compression/prs/compress.ts  | 30 +++++--------------
 2 files changed, 10 insertions(+), 26 deletions(-)

diff --git a/src/core/data_formats/block/cursor/BufferCursor.ts b/src/core/data_formats/block/cursor/BufferCursor.ts
index ba21e38b..da6ceca5 100644
--- a/src/core/data_formats/block/cursor/BufferCursor.ts
+++ b/src/core/data_formats/block/cursor/BufferCursor.ts
@@ -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.`);
         }
 
diff --git a/src/core/data_formats/compression/prs/compress.ts b/src/core/data_formats/compression/prs/compress.ts
index 62bad34e..cf34c34a 100644
--- a/src/core/data_formats/compression/prs/compress.ts
+++ b/src/core/data_formats/compression/prs/compress.ts
@@ -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);