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

[Junio C Hamano <gitster@pobox.com>]

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;
}