static int reuse_worktree_file(const char *name, const unsigned char *sha1, int want_file)
{
	struct cache_entry *ce;
	struct stat st;
	int pos, len;

	/* We do not read the cache ourselves here, because the
	 * benchmark with my previous version that always reads cache
	 * shows that it makes things worse for diff-tree comparing
	 * two linux-2.6 kernel trees in an already checked out work
	 * tree.  This is because most diff-tree comparisons deal with
	 * only a small number of files, while reading the cache is
	 * expensive for a large project, and its cost outweighs the
	 * savings we get by not inflating the object to a temporary
	 * file.  Practically, this code only helps when we are used
	 * by diff-cache --cached, which does read the cache before
	 * calling us.
	 */
	if (!active_cache)
		return 0;

	/* We want to avoid the working directory if our caller
	 * doesn't need the data in a normal file, this system
	 * is rather slow with its stat/open/mmap/close syscalls,
	 * and the object is contained in a pack file.  The pack
	 * is probably already open and will be faster to obtain
	 * the data through than the working directory.  Loose
	 * objects however would tend to be slower as they need
	 * to be individually opened and inflated.
	 */
	if (!FAST_WORKING_DIRECTORY && !want_file && has_sha1_pack(sha1, NULL))
		return 0;

	len = strlen(name);
	pos = cache_name_pos(name, len);
	if (pos < 0)
		return 0;
	ce = active_cache[pos];

	/*
	 * This is not the sha1 we are looking for, or
	 * unreusable because it is not a regular file.
	 */
	if (hashcmp(sha1, ce->sha1) || !S_ISREG(ce->ce_mode))
		return 0;

	/*
	 * If ce matches the file in the work tree, we can reuse it.
	 */
	if (ce_uptodate(ce) ||
	    (!lstat(name, &st) && !ce_match_stat(ce, &st, 0)))
		return 1;

	return 0;
}
Unknown