/**
 * ntfs_rl_vcn_to_lcn - convert a vcn into a lcn given a runlist
 * @rl:		runlist to use for conversion
 * @vcn:	vcn to convert
 *
 * Convert the virtual cluster number @vcn of an attribute into a logical
 * cluster number (lcn) of a device using the runlist @rl to map vcns to their
 * corresponding lcns.
 *
 * Since lcns must be >= 0, we use negative return values with special meaning:
 *
 * Return value			Meaning / Description
 * ==================================================
 *  -1 = LCN_HOLE		Hole / not allocated on disk.
 *  -2 = LCN_RL_NOT_MAPPED	This is part of the runlist which has not been
 *				inserted into the runlist yet.
 *  -3 = LCN_ENOENT		There is no such vcn in the attribute.
 *  -4 = LCN_EINVAL		Input parameter error.
 */
LCN ntfs_rl_vcn_to_lcn(const runlist_element *rl, const VCN vcn)
{
	int i;

	if (vcn < (VCN)0)
		return (LCN)LCN_EINVAL;
	/*
	 * If rl is NULL, assume that we have found an unmapped runlist. The
	 * caller can then attempt to map it and fail appropriately if
	 * necessary.
	 */
	if (!rl)
		return (LCN)LCN_RL_NOT_MAPPED;

	/* Catch out of lower bounds vcn. */
	if (vcn < rl[0].vcn)
		return (LCN)LCN_ENOENT;

	for (i = 0; rl[i].length; i++) {
		if (vcn < rl[i+1].vcn) {
			if (rl[i].lcn >= (LCN)0)
				return rl[i].lcn + (vcn - rl[i].vcn);
			return rl[i].lcn;
		}
	}
	/*
	 * The terminator element is setup to the correct value, i.e. one of
	 * LCN_HOLE, LCN_RL_NOT_MAPPED, or LCN_ENOENT.
	 */
	if (rl[i].lcn < (LCN)0)
		return rl[i].lcn;
	/* Just in case... We could replace this with BUG() some day. */
	return (LCN)LCN_ENOENT;
}