How would you make this switch statement as fast as possible?

Question

2009-12-04 UPDATE: For profiling results on a number of the suggestions posted here, see below!

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The Question

Consider the following very

Answer 1

Trade memory for speed by pre-populating an index table to leverage simple pointer arithmetic.

public class Service 
{
    public static MarketDataExchange GetMarketDataExchange(string ActivCode) {
    {
        int x = 65, y = 65;
        switch(ActivCode.Length)
        {
            case 1:
                x = ActivCode[0];
                break;
            case 2:
                x = ActivCode[0];
                y = ActivCode[1];
                break;
        }
        return _table[x, y];
    }

    static Service()
    {
        InitTable();
    }

    public static MarketDataExchange[,] _table = 
        new MarketDataExchange['Z','Z'];

    public static void InitTable()
    {
        for (int x = 0; x < 'Z'; x++)
            for (int y = 0; y < 'Z'; y++)
                _table[x, y] = MarketDataExchange.NONE;

        SetCell("", MarketDataExchange.NBBO);
        SetCell("A", MarketDataExchange.AMEX);
        SetCell("B", MarketDataExchange.BSE);
        SetCell("BT", MarketDataExchange.BATS);
        SetCell("C", MarketDataExchange.NSE);
        SetCell("MW", MarketDataExchange.CHX);
        SetCell("N", MarketDataExchange.NYSE);
        SetCell("PA", MarketDataExchange.ARCA);
        SetCell("Q", MarketDataExchange.NASDAQ);
        SetCell("QD", MarketDataExchange.NASDAQ_ADF);
        SetCell("W", MarketDataExchange.CBOE);
        SetCell("X", MarketDataExchange.PHLX);
        SetCell("Y", MarketDataExchange.DIRECTEDGE);
    }

    private static void SetCell(string s, MarketDataExchange exchange)
    {
        char x = 'A', y = 'A';
        switch(s.Length)
        {
            case 1:
                x = s[0];
                break;
            case 2:
                x = s[0];
                y = s[1];
                break;
        }
        _table[x, y] = exchange;
    }
}

Make the enum byte-based to save a little space.

public enum MarketDataExchange : byte
{
    NBBO, AMEX, BSE, BATS, NSE, CHX, NYSE, ARCA, 
    NASDAQ, NASDAQ_ADF, CBOE, PHLIX, DIRECTEDGE, NONE
}