archive: make zip compression level independent from core git

zlib_compression_level is the compression level used for git's object store.
It's 1 by default, which is the fastest setting.  This variable is also used
as the default compression level for ZIP archives created by git archive.

For archives, however, zlib's own default of 6 is more appropriate, as it's
favouring small size over speed -- archive creation is not that performance
critical most of the time.

This patch makes git archive independent from git's internal compression
level setting.  It affects invocations of git archive without explicitly
specified compression level option, only.

Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

archive-zip.c

@@ -93,15 +93,15 @@ static void copy_le32(unsigned char *dest, unsigned int n)
 }
 
 static void *zlib_deflate(void *data, unsigned long size,
-                          unsigned long *compressed_size)
+		int compression_level, unsigned long *compressed_size)
 {
 	z_stream stream;
 	unsigned long maxsize;
 	void *buffer;
 	int result;
 
 	memset(&stream, 0, sizeof(stream));
-	deflateInit(&stream, zlib_compression_level);
+	deflateInit(&stream, compression_level);
 	maxsize = deflateBound(&stream, size);
 	buffer = xmalloc(maxsize);
 
@@ -157,7 +157,7 @@ static int write_zip_entry(struct archiver_args *args,
 		method = 0;
 		attr2 = S_ISLNK(mode) ? ((mode | 0777) << 16) :
 			(mode & 0111) ? ((mode) << 16) : 0;
-		if (S_ISREG(mode) && zlib_compression_level != 0)
+		if (S_ISREG(mode) && args->compression_level != 0)
 			method = 8;
 		crc = crc32(crc, buffer, size);
 		out = buffer;
@@ -169,7 +169,8 @@ static int write_zip_entry(struct archiver_args *args,
 	}
 
 	if (method == 8) {
-		deflated = zlib_deflate(buffer, size, &compressed_size);
+		deflated = zlib_deflate(buffer, size, args->compression_level,
+				&compressed_size);
 		if (deflated && compressed_size - 6 < size) {
 			/* ZLIB --> raw compressed data (see RFC 1950) */
 			/* CMF and FLG ... */

archive.h

@@ -13,6 +13,7 @@ struct archiver_args {
 	time_t time;
 	const char **pathspec;
 	unsigned int verbose : 1;
+	int compression_level;
 };
 
 typedef int (*write_archive_fn_t)(struct archiver_args *);

builtin-archive.c

@@ -185,9 +185,10 @@ int parse_archive_args(int argc, const char **argv, const struct archiver **ar,
 	if (!*ar)
 		die("Unknown archive format '%s'", format);
 
+	args->compression_level = Z_DEFAULT_COMPRESSION;
 	if (compression_level != -1) {
 		if ((*ar)->flags & USES_ZLIB_COMPRESSION)
-			zlib_compression_level = compression_level;
+			args->compression_level = compression_level;
 		else {
 			die("Argument not supported for format '%s': -%d",
 					format, compression_level);