Move hasher to separate function

nodeca · Nov 12, 2020 · 677ba48 · 677ba48
1 parent 5638105
commit 677ba48
Showing 1 changed file with 15 additions and 8 deletions.
diff --git a/lib/zlib/deflate.js b/lib/zlib/deflate.js
@@ -96,6 +96,13 @@ const zero = (buf) => {
 };
 
 
+/* eslint-disable new-cap */
+let HASH_ZLIB = (s, prev, data) => ((prev << s.hash_shift) ^ data) & s.hash_mask;
+// This hash causes less collisions, https://github.com/nodeca/pako/issues/135
+// But breaks binary compatibility
+//let HASH_FAST = (s, prev, data) => ((prev << 8) + (prev >> 8) + (data << 4)) & s.hash_mask;
+let HASH = HASH_ZLIB;
+
 /* =========================================================================
  * Flush as much pending output as possible. All deflate() output goes
  * through this function so some applications may wish to modify it
@@ -395,13 +402,13 @@ const fill_window = (s) => {
       s.ins_h = s.window[str];
 
       /* UPDATE_HASH(s, s->ins_h, s->window[str + 1]); */
-      s.ins_h = ((s.ins_h << s.hash_shift) ^ s.window[str + 1]) & s.hash_mask;
+      s.ins_h = HASH(s, s.ins_h, s.window[str + 1]);
 //#if MIN_MATCH != 3
 //        Call update_hash() MIN_MATCH-3 more times
 //#endif
       while (s.insert) {
         /* UPDATE_HASH(s, s->ins_h, s->window[str + MIN_MATCH-1]); */
-        s.ins_h = ((s.ins_h << s.hash_shift) ^ s.window[str + MIN_MATCH - 1]) & s.hash_mask;
+        s.ins_h = HASH(s, s.ins_h, s.window[str + MIN_MATCH - 1]);
 
         s.prev[str & s.w_mask] = s.head[s.ins_h];
         s.head[s.ins_h] = str;
@@ -591,7 +598,7 @@ const deflate_fast = (s, flush) => {
     hash_head = 0/*NIL*/;
     if (s.lookahead >= MIN_MATCH) {
       /*** INSERT_STRING(s, s.strstart, hash_head); ***/
-      s.ins_h = ((s.ins_h << s.hash_shift) ^ s.window[s.strstart + MIN_MATCH - 1]) & s.hash_mask;
+      s.ins_h = HASH(s, s.ins_h, s.window[s.strstart + MIN_MATCH - 1]);
       hash_head = s.prev[s.strstart & s.w_mask] = s.head[s.ins_h];
       s.head[s.ins_h] = s.strstart;
       /***/
@@ -625,7 +632,7 @@ const deflate_fast = (s, flush) => {
         do {
           s.strstart++;
           /*** INSERT_STRING(s, s.strstart, hash_head); ***/
-          s.ins_h = ((s.ins_h << s.hash_shift) ^ s.window[s.strstart + MIN_MATCH - 1]) & s.hash_mask;
+          s.ins_h = HASH(s, s.ins_h, s.window[s.strstart + MIN_MATCH - 1]);
           hash_head = s.prev[s.strstart & s.w_mask] = s.head[s.ins_h];
           s.head[s.ins_h] = s.strstart;
           /***/
@@ -640,7 +647,7 @@ const deflate_fast = (s, flush) => {
         s.match_length = 0;
         s.ins_h = s.window[s.strstart];
         /* UPDATE_HASH(s, s.ins_h, s.window[s.strstart+1]); */
-        s.ins_h = ((s.ins_h << s.hash_shift) ^ s.window[s.strstart + 1]) & s.hash_mask;
+        s.ins_h = HASH(s, s.ins_h, s.window[s.strstart + 1]);
 
 //#if MIN_MATCH != 3
 //                Call UPDATE_HASH() MIN_MATCH-3 more times
@@ -721,7 +728,7 @@ const deflate_slow = (s, flush) => {
     hash_head = 0/*NIL*/;
     if (s.lookahead >= MIN_MATCH) {
       /*** INSERT_STRING(s, s.strstart, hash_head); ***/
-      s.ins_h = ((s.ins_h << s.hash_shift) ^ s.window[s.strstart + MIN_MATCH - 1]) & s.hash_mask;
+      s.ins_h = HASH(s, s.ins_h, s.window[s.strstart + MIN_MATCH - 1]);
       hash_head = s.prev[s.strstart & s.w_mask] = s.head[s.ins_h];
       s.head[s.ins_h] = s.strstart;
       /***/
@@ -773,7 +780,7 @@ const deflate_slow = (s, flush) => {
       do {
         if (++s.strstart <= max_insert) {
           /*** INSERT_STRING(s, s.strstart, hash_head); ***/
-          s.ins_h = ((s.ins_h << s.hash_shift) ^ s.window[s.strstart + MIN_MATCH - 1]) & s.hash_mask;
+          s.ins_h = HASH(s, s.ins_h, s.window[s.strstart + MIN_MATCH - 1]);
           hash_head = s.prev[s.strstart & s.w_mask] = s.head[s.ins_h];
           s.head[s.ins_h] = s.strstart;
           /***/
@@ -1798,7 +1805,7 @@ const deflateSetDictionary = (strm, dictionary) => {
     let n = s.lookahead - (MIN_MATCH - 1);
     do {
       /* UPDATE_HASH(s, s->ins_h, s->window[str + MIN_MATCH-1]); */
-      s.ins_h = ((s.ins_h << s.hash_shift) ^ s.window[str + MIN_MATCH - 1]) & s.hash_mask;
+      s.ins_h = HASH(s, s.ins_h, s.window[str + MIN_MATCH - 1]);
 
       s.prev[str & s.w_mask] = s.head[s.ins_h];