Re: [PATCH] common_prefix: be more careful about pathspec bounds

From: Junio C Hamano <gitster@pobox.com>
Date: Jun 15, 2010, 16:06 UTC
Message-ID: <7v4oh48elm.fsf@alter.siamese.dyndns.org>
In-Reply-To: <7v8w6g8hfx.fsf@alter.siamese.dyndns.org>

Junio C Hamano <gitster@pobox.com> writes:

> Isn't it more intuitive to structure the loop by saying 'Ok, if "path" up
> to the currently proposed "prefix" is too long to match, let's shorten it
> by one path component and try again'?

Another way of saying this, which probably needs less number of scans, would be to shorten prefix to what is known to match --- use of memcmp() discards this information.

static int common_prefix(const char **pathspec)
{
	const char *path, *slash, *next;
	int prefix;

	if (!pathspec)
		return 0;

	path = *pathspec;
	slash = strrchr(path, '/');
	if (!slash)
		return 0;
	prefix = slash - path + 1;

	while ((next = *++pathspec) != NULL) {
		int len, last_matching_slash = -1;
		for (len = 0;
		     len < prefix && next[len] == path[len];
		     len++)
			if (next[len] == '/')
				last_matching_slash = len;
		if (len == prefix)
			continue;
		if (last_matching_slash < 0)
			return 0;
		prefix = last_matching_slash + 1;
	}
	return prefix;
}