presto-main/src/main/java/io/prestosql/operator/window/NTileFunction.java/NTileFunction/processRow
class NTileFunction:    @Override
    public void processRow(BlockBuilder output, boolean newPeerGroup, int peerGroupCount, int currentPosition)
    {
        if (windowIndex.isNull(valueChannel, currentPosition)) {
            output.appendNull();
        }
        else {
            long buckets = windowIndex.getLong(valueChannel, currentPosition);
            checkCondition(buckets > 0, INVALID_FUNCTION_ARGUMENT, "Buckets must be greater than 0");
            BIGINT.writeLong(output, bucket(buckets, currentPosition) + 1);
        }
    }