From: Nicolas Pitre <nico@cam.org>
Date: Wed, 29 Jun 2005 04:27:45 +0000 (-0400)
Subject: [PATCH] denser delta header encoding
X-Git-Tag: v0.99~132
X-Git-Url: https://git.verplant.org/?a=commitdiff_plain;h=69a2d426f0d249bca2c6f754b3c1283c0fa72fd4;p=git.git

[PATCH] denser delta header encoding

Since the delta data format is not tied to any actual git object
anymore, now is the time to add a small improvement to the delta data
header as it is been done for packed object header.  This patch allows
for reducing the delta header of about 2 bytes and makes for simpler
code.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
---

diff --git a/count-delta.c b/count-delta.c
index c7f37678..89010341 100644
--- a/count-delta.c
+++ b/count-delta.c
@@ -11,16 +11,13 @@
 static unsigned long get_hdr_size(const unsigned char **datap)
 {
 	const unsigned char *data = *datap;
-	unsigned long size;
-	unsigned char cmd;
-	int i;
-	size = i = 0;
-	cmd = *data++;
-	while (cmd) {
-		if (cmd & 1)
-			size |= *data++ << i;
-		i += 8;
-		cmd >>= 1;
+	unsigned char cmd = *data++;
+	unsigned long size = cmd & ~0x80;
+	int i = 7;
+	while (cmd & 0x80) {
+		cmd = *data++;
+		size |= (cmd & ~0x80) << i;
+		i += 7;
 	}
 	*datap = data;
 	return size;
@@ -47,8 +44,8 @@ int count_delta(void *delta_buf, unsigned long delta_size,
 	unsigned char cmd;
 	unsigned long src_size, dst_size, out;
 
-	/* the smallest delta size possible is 6 bytes */
-	if (delta_size < 6)
+	/* the smallest delta size possible is 4 bytes */
+	if (delta_size < 4)
 		return -1;
 
 	data = delta_buf;
diff --git a/diff-delta.c b/diff-delta.c
index fd9b37f4..67f60814 100644
--- a/diff-delta.c
+++ b/diff-delta.c
@@ -228,28 +228,22 @@ void *diff_delta(void *from_buf, unsigned long from_size,
 	top = to_buf + to_size;
 
 	/* store reference buffer size */
-	orig = out + outpos++;
-	*orig = i = 0;
-	do {
-		if (from_size & 0xff) {
-			*orig |= (1 << i);
-			out[outpos++] = from_size;
-		}
-		i++;
-		from_size >>= 8;
-	} while (from_size);
+	out[outpos++] = from_size;
+	from_size >>= 7;
+	while (from_size) {
+		out[outpos - 1] |= 0x80;
+		out[outpos++] = from_size;
+		from_size >>= 7;
+	}
 
 	/* store target buffer size */
-	orig = out + outpos++;
-	*orig = i = 0;
-	do {
-		if (to_size & 0xff) {
-			*orig |= (1 << i);
-			out[outpos++] = to_size;
-		}
-		i++;
-		to_size >>= 8;
-	} while (to_size);
+	out[outpos++] = to_size;
+	to_size >>= 7;
+	while (to_size) {
+		out[outpos - 1] |= 0x80;
+		out[outpos++] = to_size;
+		to_size >>= 7;
+	}
 
 	inscnt = 0;
 	moff = 0;
diff --git a/patch-delta.c b/patch-delta.c
index a8d75ee1..b68dd13c 100644
--- a/patch-delta.c
+++ b/patch-delta.c
@@ -22,33 +22,33 @@ void *patch_delta(void *src_buf, unsigned long src_size,
 	unsigned long size;
 	int i;
 
-	/* the smallest delta size possible is 6 bytes */
-	if (delta_size < 6)
+	/* the smallest delta size possible is 4 bytes */
+	if (delta_size < 4)
 		return NULL;
 
 	data = delta_buf;
 	top = delta_buf + delta_size;
 
 	/* make sure the orig file size matches what we expect */
-	size = i = 0;
 	cmd = *data++;
-	while (cmd) {
-		if (cmd & 1)
-			size |= *data++ << i;
-		i += 8;
-		cmd >>= 1;
+	size = cmd & ~0x80;
+	i = 7;
+	while (cmd & 0x80) {
+		cmd = *data++;
+		size |= (cmd & ~0x80) << i;
+		i += 7;
 	}
 	if (size != src_size)
 		return NULL;
 
 	/* now the result size */
-	size = i = 0;
 	cmd = *data++;
-	while (cmd) {
-		if (cmd & 1)
-			size |= *data++ << i;
-		i += 8;
-		cmd >>= 1;
+	size = cmd & ~0x80;
+	i = 7;
+	while (cmd & 0x80) {
+		cmd = *data++;
+		size |= (cmd & ~0x80) << i;
+		i += 7;
 	}
 	dst_buf = malloc(size);
 	if (!dst_buf)