Re: [PATCH] Make zlib compression level configurable, and change default.

From: Linus Torvalds <torvalds@osdl.org>
Date: Jul 3, 2006, 19:33 UTC
Message-ID: <Pine.LNX.4.64.0607031226370.12404@g5.osdl.org>
In-Reply-To: <85d5cm8qfn.fsf_-_@lupus.ig3.net>

On Mon, 3 Jul 2006, Joachim B Haga wrote:

Show 5 quoted lines

> 
> 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.

My only worry is that this encodes "Z_DEFAULT_COMPRESSION" as being -1, which happens to be /true/, but I don't think that's a documented interface (you're supposed to use the Z_DEFAULT_COMPRESSION macro, which could have any value, and just _happens_ to be -1).

Is it likely to ever change from that -1? Probably not. So I think your patch is technically correct, but it might just be nicer if it did something like

	..
	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;
	}
	..

which would be safer, and a smart compiler might notice that the -1 case ends up being a no-op, and then just generate code AS IF we just had a

	if (level < -1 || level > Z_BEST_COMPRESSION)
		die(...

there.

Oh, and for all the same reasons, we should use

	int zlib_compression_level = Z_BEST_COMPRESSION;

for the default initializer.

Hmm?

		Linus