presto-iceberg/src/main/java/io/prestosql/plugin/iceberg/PartitionTransforms.java/PartitionTransforms/truncateBigint
class PartitionTransforms:    private static Block truncateBigint(Block block, int width)
    {
        BlockBuilder builder = BIGINT.createFixedSizeBlockBuilder(block.getPositionCount());
        for (int position = 0; position < block.getPositionCount(); position++) {
            if (block.isNull(position)) {
                builder.appendNull();
                continue;
            }
            long value = BIGINT.getLong(block, position);
            value -= ((value % width) + width) % width;
            BIGINT.writeLong(builder, value);
        }
        return builder.build();
    }