From: Junio C Hamano <junkio@cox.net>
Date: Tue, 28 Feb 2006 05:37:56 +0000 (-0800)
Subject: Revert "Revert "diff-delta: produce optimal pack data""
X-Git-Tag: v1.3.0-rc1~54^2~22^2~1
X-Git-Url: https://git.verplant.org/?a=commitdiff_plain;h=bec2a69fe4c2dbb377d2742a4def7e3569b4c1d4;p=git.git

Revert "Revert "diff-delta: produce optimal pack data""
---

diff --git a/diff-delta.c b/diff-delta.c
index 2ed5984b..27f83a08 100644
--- a/diff-delta.c
+++ b/diff-delta.c
@@ -20,21 +20,11 @@
 
 #include <stdlib.h>
 #include <string.h>
-#include <zlib.h>
 #include "delta.h"
 
 
-/* block size: min = 16, max = 64k, power of 2 */
-#define BLK_SIZE 16
-
-#define MIN(a, b) ((a) < (b) ? (a) : (b))
-
-#define GR_PRIME 0x9e370001
-#define HASH(v, shift) (((unsigned int)(v) * GR_PRIME) >> (shift))
-
 struct index {
 	const unsigned char *ptr;
-	unsigned int val;
 	struct index *next;
 };
 
@@ -42,21 +32,21 @@ static struct index ** delta_index(const unsigned char *buf,
 				   unsigned long bufsize,
 				   unsigned int *hash_shift)
 {
-	unsigned int hsize, hshift, entries, blksize, i;
+	unsigned long hsize;
+	unsigned int hshift, i;
 	const unsigned char *data;
 	struct index *entry, **hash;
 	void *mem;
 
 	/* determine index hash size */
-	entries = (bufsize + BLK_SIZE - 1) / BLK_SIZE;
-	hsize = entries / 4;
-	for (i = 4; (1 << i) < hsize && i < 16; i++);
+	hsize = bufsize / 4;
+	for (i = 8; (1 << i) < hsize && i < 16; i++);
 	hsize = 1 << i;
-	hshift = 32 - i;
+	hshift = i - 8;
 	*hash_shift = hshift;
 
 	/* allocate lookup index */
-	mem = malloc(hsize * sizeof(*hash) + entries * sizeof(*entry));
+	mem = malloc(hsize * sizeof(*hash) + bufsize * sizeof(*entry));
 	if (!mem)
 		return NULL;
 	hash = mem;
@@ -64,17 +54,12 @@ static struct index ** delta_index(const unsigned char *buf,
 	memset(hash, 0, hsize * sizeof(*hash));
 
 	/* then populate it */
-	data = buf + entries * BLK_SIZE - BLK_SIZE;
-	blksize = bufsize - (data - buf);
-	while (data >= buf) {
-		unsigned int val = adler32(0, data, blksize);
-		i = HASH(val, hshift);
-		entry->ptr = data;
-		entry->val = val;
+	data = buf + bufsize - 2;
+	while (data > buf) {
+		entry->ptr = --data;
+		i = data[0] ^ data[1] ^ (data[2] << hshift);
 		entry->next = hash[i];
 		hash[i] = entry++;
-		blksize = BLK_SIZE;
-		data -= BLK_SIZE;
  	}
 
 	return hash;
@@ -141,29 +126,27 @@ void *diff_delta(void *from_buf, unsigned long from_size,
 
 	while (data < top) {
 		unsigned int moff = 0, msize = 0;
-		unsigned int blksize = MIN(top - data, BLK_SIZE);
-		unsigned int val = adler32(0, data, blksize);
-		i = HASH(val, hash_shift);
-		for (entry = hash[i]; entry; entry = entry->next) {
-			const unsigned char *ref = entry->ptr;
-			const unsigned char *src = data;
-			unsigned int ref_size = ref_top - ref;
-			if (entry->val != val)
-				continue;
-			if (ref_size > top - src)
-				ref_size = top - src;
-			while (ref_size && *src++ == *ref) {
-				ref++;
-				ref_size--;
-			}
-			ref_size = ref - entry->ptr;
-			if (ref_size > msize) {
-				/* this is our best match so far */
-				moff = entry->ptr - ref_data;
-				msize = ref_size;
-				if (msize >= 0x10000) {
-					msize = 0x10000;
+		if (data + 2 < top) {
+			i = data[0] ^ data[1] ^ (data[2] << hash_shift);
+			for (entry = hash[i]; entry; entry = entry->next) {
+				const unsigned char *ref = entry->ptr;
+				const unsigned char *src = data;
+				unsigned int ref_size = ref_top - ref;
+				if (ref_size > top - src)
+					ref_size = top - src;
+				if (ref_size > 0x10000)
+					ref_size = 0x10000;
+				if (ref_size <= msize)
 					break;
+				while (ref_size && *src++ == *ref) {
+					ref++;
+					ref_size--;
+				}
+				ref_size = ref - entry->ptr;
+				if (msize < ref - entry->ptr) {
+					/* this is our best match so far */
+					msize = ref - entry->ptr;
+					moff = entry->ptr - ref_data;
 				}
 			}
 		}