Make zlib compression level configurable, and change default.

With the change in default, "git add ." on kernel dir is about
twice as fast as before, with only minimal (0.5%) change in
object size. The speed difference is even more noticeable
when committing large files, which is now up to 8 times faster.

The configurability is through setting core.compression = [-1..9]
which maps to the zlib constants; -1 is the default, 0 is no
compression, and 1..9 are various speed/size tradeoffs, 9
being slowest.

Signed-off-by: Joachim B Haga (cjhaga@fys.uio.no)
Acked-by: Linus Torvalds <torvalds@osdl.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

Documentation/config.txt

@@ -91,6 +91,12 @@ core.warnAmbiguousRefs::
 	If true, git will warn you if the ref name you passed it is ambiguous
 	and might match multiple refs in the .git/refs/ tree. True by default.
 
+core.compression:
+	An integer -1..9, indicating the compression level for objects that
+	are not in a pack file. -1 is the zlib and git default. 0 means no
+	compression, and 1..9 are various speed/size tradeoffs, 9 being
+	slowest.
+
 alias.*::
 	Command aliases for the gitlink:git[1] command wrapper - e.g.
 	after defining "alias.last = cat-file commit HEAD", the invocation

cache.h

@@ -183,6 +183,7 @@ extern int log_all_ref_updates;
 extern int warn_ambiguous_refs;
 extern int shared_repository;
 extern const char *apply_default_whitespace;
+extern int zlib_compression_level;
 
 #define GIT_REPO_VERSION 0
 extern int repository_format_version;

config.c

@@ -279,6 +279,16 @@ int git_default_config(const char *var, const char *value)
 		return 0;
 	}
 
+	if (!strcmp(var, "core.compression")) {
+		int level = git_config_int(var, value);
+		if (level == -1)
+			level = Z_DEFAULT_COMPRESSION;
+		else if (level < 0 || level > Z_BEST_COMPRESSION)
+			die("bad zlib compression level %d", level);
+		zlib_compression_level = level;
+		return 0;
+	}
+
 	if (!strcmp(var, "user.name")) {
 		strlcpy(git_default_name, value, sizeof(git_default_name));
 		return 0;

csum-file.c

@@ -122,7 +122,7 @@ int sha1write_compressed(struct sha1file *f, void *in, unsigned int size)
 	void *out;
 
 	memset(&stream, 0, sizeof(stream));
-	deflateInit(&stream, Z_DEFAULT_COMPRESSION);
+	deflateInit(&stream, zlib_compression_level);
 	maxsize = deflateBound(&stream, size);
 	out = xmalloc(maxsize);
 

diff.c

@@ -583,7 +583,7 @@ static unsigned char *deflate_it(char *data,
 	z_stream stream;
 
 	memset(&stream, 0, sizeof(stream));
-	deflateInit(&stream, Z_BEST_COMPRESSION);
+	deflateInit(&stream, zlib_compression_level);
 	bound = deflateBound(&stream, size);
 	deflated = xmalloc(bound);
 	stream.next_out = deflated;

environment.c

@@ -20,6 +20,7 @@ int repository_format_version = 0;
 char git_commit_encoding[MAX_ENCODING_LENGTH] = "utf-8";
 int shared_repository = PERM_UMASK;
 const char *apply_default_whitespace = NULL;
+int zlib_compression_level = Z_DEFAULT_COMPRESSION;
 
 static char *git_dir, *git_object_dir, *git_index_file, *git_refs_dir,
 	*git_graft_file;

http-push.c

@@ -492,7 +492,7 @@ static void start_put(struct transfer_request *request)
 
 	/* Set it up */
 	memset(&stream, 0, sizeof(stream));
-	deflateInit(&stream, Z_BEST_COMPRESSION);
+	deflateInit(&stream, zlib_compression_level);
 	size = deflateBound(&stream, len + hdrlen);
 	request->buffer.buffer = xmalloc(size);
 

sha1_file.c

@@ -1458,7 +1458,7 @@ int write_sha1_file(void *buf, unsigned long len, const char *type, unsigned cha
 
 	/* Set it up */
 	memset(&stream, 0, sizeof(stream));
-	deflateInit(&stream, Z_BEST_COMPRESSION);
+	deflateInit(&stream, zlib_compression_level);
 	size = deflateBound(&stream, len+hdrlen);
 	compressed = xmalloc(size);
 
@@ -1511,7 +1511,7 @@ static void *repack_object(const unsigned char *sha1, unsigned long *objsize)
 
 	/* Set it up */
 	memset(&stream, 0, sizeof(stream));
-	deflateInit(&stream, Z_BEST_COMPRESSION);
+	deflateInit(&stream, zlib_compression_level);
 	size = deflateBound(&stream, len + hdrlen);
 	buf = xmalloc(size);