ArraySegmentX

High performance ArraySegment<T> for C#.

The Bottleneck

Consider the following code for built in ArraySegment.

int n = segment.Array[segment.Offset + i];

IL generates two call instructions because .Array and .Offset are properties:

ArraySegmentX does not need two extra call instructions:

This is a micro optimization. In most cases, it doesn't matter. For heavy number crunching like in Mirror's delta compression, it does matter.

Benchmarks

Test.cs simple benchmarks with 1 million iterations

• byte[]: 1.5s
• ArraySegment: 3.6s
• ArraySegmentX: 1.5s

=> 2.4x faster

Mirror's delta compression with 10k iterations, 1000 bytes, 1% changes:

• byte[]: 1.7s
• ArraySegment: 6.4s
• ArraySegmentX: 1.7s

=> 3.76x faster

Convenience [] access

Unity's ArraySegment does not support direct [] access:

// supported
int n = segment.Array[segment.Offset + i];
  
// not supported
int n = segment[i];

ArraySegmentX adds [] access for covenience.

NOTE that this requires an IL call instruction. Use the long way where performance matters.