X-Git-Url: https://git.octo.it/?a=blobdiff_plain;f=diff-delta.c;h=2ed5984b1c360194d53fd287962d7857e19a097c;hb=00333ca35c5986e44d4cd4fd59433200d916f77e;hp=0730b24df8fe679d16e1cd03d066b4d7f33e73cd;hpb=1025fe51bf540bc4c63bce2553a43b1c753e1c40;p=git.git

diff --git a/diff-delta.c b/diff-delta.c
index 0730b24d..2ed5984b 100644
--- a/diff-delta.c
+++ b/diff-delta.c
@@ -20,93 +20,63 @@
 
 #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;
 };
 
 static struct index ** delta_index(const unsigned char *buf,
 				   unsigned long bufsize,
-				   unsigned long trg_bufsize,
 				   unsigned int *hash_shift)
 {
-	unsigned long hsize;
-	unsigned int i, hshift, hlimit, *hash_count;
+	unsigned int hsize, hshift, entries, blksize, i;
 	const unsigned char *data;
 	struct index *entry, **hash;
 	void *mem;
 
 	/* determine index hash size */
-	hsize = bufsize / 4;
-	for (i = 8; (1 << i) < hsize && i < 24; i += 2);
+	entries = (bufsize + BLK_SIZE - 1) / BLK_SIZE;
+	hsize = entries / 4;
+	for (i = 4; (1 << i) < hsize && i < 16; i++);
 	hsize = 1 << i;
-	hshift = (i - 8) / 2;
+	hshift = 32 - i;
 	*hash_shift = hshift;
 
 	/* allocate lookup index */
-	mem = malloc(hsize * sizeof(*hash) + bufsize * sizeof(*entry));
+	mem = malloc(hsize * sizeof(*hash) + entries * sizeof(*entry));
 	if (!mem)
 		return NULL;
 	hash = mem;
 	entry = mem + hsize * sizeof(*hash);
 	memset(hash, 0, hsize * sizeof(*hash));
 
-	/* allocate an array to count hash entries */
-	hash_count = calloc(hsize, sizeof(*hash_count));
-	if (!hash_count) {
-		free(hash);
-		return NULL;
-	}
-
-	/* then populate the index */
-	data = buf + bufsize - 2;
-	while (data > buf) {
-		entry->ptr = --data;
-		i = data[0] ^ ((data[1] ^ (data[2] << hshift)) << hshift);
+	/* 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;
 		entry->next = hash[i];
 		hash[i] = entry++;
-		hash_count[i]++;
+		blksize = BLK_SIZE;
+		data -= BLK_SIZE;
  	}
 
-	/*
-	 * Determine a limit on the number of entries in the same hash
-	 * bucket.  This guard us against patological data sets causing
-	 * really bad hash distribution with most entries in the same hash
-	 * bucket that would bring us to O(m*n) computing costs (m and n
-	 * corresponding to reference and target buffer sizes).
-	 *
-	 * The more the target buffer is large, the more it is important to
-	 * have small entry lists for each hash buckets.  With such a limit
-	 * the cost is bounded to something more like O(m+n).
-	 */
-	hlimit = (1 << 26) / trg_bufsize;
-	if (hlimit < 16)
-		hlimit = 16;
-
-	/*
-	 * Now make sure none of the hash buckets has more entries than
-	 * we're willing to test.  Otherwise we short-circuit the entry
-	 * list uniformly to still preserve a good repartition across
-	 * the reference buffer.
-	 */
-	for (i = 0; i < hsize; i++) {
-		if (hash_count[i] < hlimit)
-			continue;
-		entry = hash[i];
-		do {
-			struct index *keep = entry;
-			int skip = hash_count[i] / hlimit / 2;
-			do {
-				entry = entry->next;
-			} while(--skip && entry);
-			keep->next = entry;
-		} while(entry);
-	}
-	free(hash_count);
-
 	return hash;
 }
 
@@ -130,7 +100,7 @@ void *diff_delta(void *from_buf, unsigned long from_size,
 
 	if (!from_size || !to_size)
 		return NULL;
-	hash = delta_index(from_buf, from_size, to_size, &hash_shift);
+	hash = delta_index(from_buf, from_size, &hash_shift);
 	if (!hash)
 		return NULL;
 
@@ -171,25 +141,29 @@ void *diff_delta(void *from_buf, unsigned long from_size,
 
 	while (data < top) {
 		unsigned int moff = 0, msize = 0;
-		if (data + 3 <= top) {
-			i = data[0] ^ ((data[1] ^ (data[2] << hash_shift)) << 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)
+		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;
 					break;
-				if (*ref != *src)
-					continue;
-				while (ref_size-- && *++src == *++ref);
-				if (msize < ref - entry->ptr) {
-					/* this is our best match so far */
-					msize = ref - entry->ptr;
-					moff = entry->ptr - ref_data;
 				}
 			}
 		}