X-Git-Url: https://git.octo.it/?a=blobdiff_plain;f=diff-delta.c;h=1188b31cd0f1e2f3a1fc2096a10243a03b439021;hb=e464f4c3119b04712ab87329f3dd4d4f21b0a8a7;hp=0730b24df8fe679d16e1cd03d066b4d7f33e73cd;hpb=213523f46c51c5e5f1b2623dcb3af822add75caa;p=git.git

diff --git a/diff-delta.c b/diff-delta.c
index 0730b24d..1188b31c 100644
--- a/diff-delta.c
+++ b/diff-delta.c
@@ -20,11 +20,21 @@
 
 #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;
 };
 
@@ -33,21 +43,21 @@ static struct index ** delta_index(const unsigned char *buf,
 				   unsigned long trg_bufsize,
 				   unsigned int *hash_shift)
 {
-	unsigned long hsize;
-	unsigned int i, hshift, hlimit, *hash_count;
+	unsigned int i, hsize, hshift, hlimit, entries, *hash_count;
 	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;
+	hsize = entries / 4;
+	for (i = 4; (1 << i) < hsize && i < 31; 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;
@@ -62,13 +72,16 @@ static struct index ** delta_index(const unsigned char *buf,
 	}
 
 	/* then populate the index */
-	data = buf + bufsize - 2;
-	while (data > buf) {
-		entry->ptr = --data;
-		i = data[0] ^ ((data[1] ^ (data[2] << hshift)) << hshift);
+	data = buf + entries * BLK_SIZE - BLK_SIZE;
+	while (data >= buf) {
+		unsigned int val = adler32(0, data, BLK_SIZE);
+		i = HASH(val, hshift);
+		entry->ptr = data;
+		entry->val = val;
 		entry->next = hash[i];
 		hash[i] = entry++;
 		hash_count[i]++;
+		data -= BLK_SIZE;
  	}
 
 	/*
@@ -83,13 +96,13 @@ static struct index ** delta_index(const unsigned char *buf,
 	 * the cost is bounded to something more like O(m+n).
 	 */
 	hlimit = (1 << 26) / trg_bufsize;
-	if (hlimit < 16)
-		hlimit = 16;
+	if (hlimit < 4*BLK_SIZE)
+		hlimit = 4*BLK_SIZE;
 
 	/*
 	 * 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
+	 * we're willing to test.  Otherwise we cull the entry list
+	 * uniformly to still preserve a good repartition across
 	 * the reference buffer.
 	 */
 	for (i = 0; i < hsize; i++) {
@@ -123,7 +136,8 @@ void *diff_delta(void *from_buf, unsigned long from_size,
 		 unsigned long *delta_size,
 		 unsigned long max_size)
 {
-	unsigned int i, outpos, outsize, inscnt, hash_shift;
+	unsigned int i, outpos, outsize, hash_shift;
+	int inscnt;
 	const unsigned char *ref_data, *ref_top, *data, *top;
 	unsigned char *out;
 	struct index *entry, **hash;
@@ -171,21 +185,23 @@ 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);
+		if (data + BLK_SIZE <= top) {
+			unsigned int val = adler32(0, data, BLK_SIZE);
+			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;
 				if (ref_size > 0x10000)
 					ref_size = 0x10000;
 				if (ref_size <= msize)
 					break;
-				if (*ref != *src)
-					continue;
-				while (ref_size-- && *++src == *++ref);
+				while (ref_size-- && *src++ == *ref)
+					ref++;
 				if (msize < ref - entry->ptr) {
 					/* this is our best match so far */
 					msize = ref - entry->ptr;
@@ -207,6 +223,20 @@ void *diff_delta(void *from_buf, unsigned long from_size,
 			unsigned char *op;
 
 			if (inscnt) {
+				while (moff && ref_data[moff-1] == data[-1]) {
+					if (msize == 0x10000)
+						break;
+					/* we can match one byte back */
+					msize++;
+					moff--;
+					data--;
+					outpos--;
+					if (--inscnt)
+						continue;
+					outpos--;  /* remove count slot */
+					inscnt--;  /* make it -1 */
+					break;
+				}
 				out[outpos - inscnt - 1] = inscnt;
 				inscnt = 0;
 			}