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

Junio C Hamano [off-list ref] 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;
}