ArraySegment<T> performance on tight-loops

gistfile1.cs

        static float[] data = new float[1000000];

        static void Main(string[] args)
        {
            int offset = 49421;

            Stopwatch watch = new Stopwatch();
            watch.Start();

            float t = 0;
            for (int tries = 0; tries < 1000; tries++)
            {
                for (int i = 0; i < 100000; i++)
                {
                    t = data[i];
                }
            }
            Console.WriteLine("Access without offset: " + watch.ElapsedMilliseconds + "ms.");
            // Avoid the read optimization;
            Console.WriteLine(t);

            watch.Restart();
            for (int tries = 0; tries < 1000; tries++)
            {
                for (int i = 0; i < 100000; i++)
                {
                    t = data[offset + i];
                }
            }
            Console.WriteLine("Access via offset: " + watch.ElapsedMilliseconds + "ms.");
            // Avoid the read optimization;
            Console.WriteLine(t);

            var segment = new ArraySegment<float>(data, offset, 100000);
            watch.Restart();
            for (int tries = 0; tries < 1000; tries++)
            {
                for (int i = 0; i < 100000; i++)
                {
                    t = data[i];
                }
            }
            Console.WriteLine("Access via array segment: " + watch.ElapsedMilliseconds + "ms.");

            // Avoid the read optimization;
            Console.WriteLine(t);
            Console.ReadLine();
        }

Access without offset: 120ms.
Access via offset: 118ms.
Access via array segment: 118ms.

You made a mistake. You need to index segment instead of data. Indexing segment requires a cast to IList.