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My C# solution to the One Billion Row Challenge

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# The One Billion Row Challenge
This is my C# implementation for the One Billion Row Challenge (1BRC) as defined in the [gunnarmorling/1brc](https://github.com/gunnarmorling/1brc) GitHub repository.

## Running my solution
Make sure you have the latest .NET 8 SDK installed. Building the project is done using the following commands (change the runtime identifier from win-x64 to the [one for your OS](https://learn.microsoft.com/en-us/dotnet/core/rid-catalog)):

```cmd
dotnet build -c Release
dotnet publish -r win-x64 -c Release
```

Then you can find the `1brc.exe` inside the `bin/Release/net8.0/publish/win-x64` directory. This executable takes a single argument which is the file path to the measurements file.

While my solution doesn't require AVX2, it is written assuming that it is available on the machine this is running on. If AVX2 is not available, then it will fall back to simulating 256-bit vectors using two 128-bit vectors as is provided by the `Vector256` type in the standard library.

## Measurements
My system has the following specs
- CPU: AMD Ryzen 9 5950X @ 3.4GHz (default clock speed)
- RAM: 32GB 3600MHz DDR4
- SSD: Samsung 980 PRO
- OS: Windows 11

I generated my input file using the `CreateMeasurements` script from the original repo. They recently changed it so that it doesn't generate carriage returns on Windows, so my solution assumes that lines are separated only by newlines.

I have a `Stopwatch` that is started when the program starts and prints the elapsed time just before the program exits. I also am using [pbench](https://github.com/chemodax/pbench) to time how long it takes to invoke the whole program so that it includes the time spent launching the runtime. I have my application compiled with NativeAOT so there is no JIT needed.

After running my program 10 times in a row, these are my measurements on my system:
- Stopwatch: Min=1.318s, Avg=1.335s, Max=1.350s
- Process Time: Min=1.329s, Avg=1.346s, Max=1.361s

## Comparison to other solutions
I also ran [buybackoff's C# solution](https://github.com/buybackoff/1brc) which also has a Stopwatch at the start and stop of the program. I noticed when running it that there was a much larger gap between the Stopwatch time and the process time. I believe this is because the stopwatch time is not timing how long it takes to close/dispose any of the file handles. I have a suspicion that maybe these issues are only showing up because I am using Windows and the results would be different on Linux.

And I also ran [royvanrijn's Java solution](https://github.com/gunnarmorling/1brc/blob/main/src/main/java/dev/morling/onebrc/CalculateAverage_royvanrijn.java) which is currently winning the competition in the original repo. I ran it using the latest GraalVM JDK. It does not have a stopwatch in the source code, so I can only time the whole process time.

buybackoff's C# solution:
- Stopwatch: Min=1.433s, Avg=1.453s, Max=1.503s
- Process Time: Min=2.202s, Avg=2.215s, Max=2.270s

royvanrijn's Java solution:
- Process Time: Min=2.501s, Avg=2.549s, Max=2.597s

Right now I'm still waiting for some other people to test out my code on their hardware and get some more performance measurements. In particular I would like to see how it fares when comparing on Linux instead of Windows, as it may be that this improved performance is not reproducible on Linux. I would take these comparisons with a grain of salt for now until then.

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