From: Hans Kristian Rosbach <hk-git@circlestorm.org>
Date: Fri, 21 Aug 2020 14:17:55 +0000 (+0200)
Subject: Increase hash table size from 15 to 16 bits.
X-Git-Tag: 1.9.9-b1~75
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=cbc3962b937315ccfb0108a6a96ee005328f467c;p=thirdparty%2Fzlib-ng.git

Increase hash table size from 15 to 16 bits.
This gives a good performance increase, and usually also improves compression.
Make separate define HASH_SLIDE for fallback version of UPDATE_HASH.
---

diff --git a/deflate.h b/deflate.h
index f9db02bb..ef84bde0 100644
--- a/deflate.h
+++ b/deflate.h
@@ -68,9 +68,9 @@
 #define FINISH_STATE 666    /* stream complete */
 /* Stream status */
 
-#define HASH_BITS 15        /* log2(HASH_SIZE) */
-#define HASH_SIZE 32768     /* number of elements in hash table */
-#define HASH_MASK 0x7FFF    /* HASH_SIZE-1 */
+#define HASH_BITS    16u           /* log2(HASH_SIZE) */
+#define HASH_SIZE 65536u           /* number of elements in hash table */
+#define HASH_MASK (HASH_SIZE - 1u) /* HASH_SIZE-1 */
 
 
 /* Data structure describing a single value and its code string. */
diff --git a/insert_string.c b/insert_string.c
index 72336681..4ddf9ae5 100644
--- a/insert_string.c
+++ b/insert_string.c
@@ -14,8 +14,10 @@
  *    input characters, so that a running hash key can be computed from the
  *    previous key instead of complete recalculation each time.
  */
+#define HASH_SLIDE 16  // Number of bits to slide hash
+
 #define UPDATE_HASH(s, h, val) \
-    h = ((val * 2654435761U) >> (32 - HASH_BITS));
+    h = ((val * 2654435761U) >> HASH_SLIDE);
 
 #define INSERT_STRING       insert_string_c
 #define QUICK_INSERT_STRING quick_insert_string_c