# ReadPackedULongDelta(ulong, in StreamCompressionModel)

> Reads an 8-byte unsigned long delta value from the data stream using a StreamCompressionModel.

## Definition

* **Type:** Method
* **Namespace:** [Unity.Collections](/engine/6000.7/script-reference/unity/collections.md)
* **Assembly:** UnityEngine.ManagedKernelModule

## ReadPackedULongDelta(ulong, StreamCompressionModel)

```csharp
public ulong ReadPackedULongDelta(ulong baseline, in StreamCompressionModel model)
```

### Parameters

**** (\[ulong]\(https\://learn.microsoft.com/dotnet/api/system.uint64)): The previous 8-byte unsigned long value, used to compute the diff.**** (\[StreamCompressionModel]\(/engine/6000.7/script-reference/unity/collections/streamcompressionmodel)): [StreamCompressionModel](/engine/6000.7/script-reference/unity/collections/streamcompressionmodel.md) model for reading value in a packed manner.

### Returns

| Type                                                          | Description                                                                                                                                            |
| ------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------ |
| [ulong](https://learn.microsoft.com/dotnet/api/system.uint64) | An 8-byte unsigned long read from the current stream, or 0 if the end of the stream has been reached. If the data did not change, this also returns 0. |