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

If the enumeration values are arbitrary you could do this...

public static MarketDataExchange GetValue(string input)
{
    switch (input.Length)
    {
        case 0: return MarketDataExchange.NBBO;
        case 1: return (MarketDataExchange)input[0];
        case 2: return (MarketDataExchange)(input[0] << 8 | input[1]);
        default: return MarketDataExchange.None;
    }
}

... if you want to go totally nuts you can also use an unsafe call with pointers as noted by Pavel Minaev ... The pure cast version above is faster than this unsafe version.

unsafe static MarketDataExchange GetValue(string input)
{
    if (input.Length == 1)
        return (MarketDataExchange)(input[0]);
    fixed (char* buffer = input)
        return (MarketDataExchange)(buffer[0] << 8 | buffer[1]);
}

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public enum MarketDataExchange
{
    NBBO = 0x00, //
    AMEX = 0x41, //A
    BSE = 0x42, //B
    BATS = 0x4254, //BT
    NSE = 0x43, //C
    CHX = 0x4D57, //MW
    NYSE = 0x4E, //N
    ARCA = 0x5041, //PA
    NASDAQ = 0x51, //Q
    NASDAQ_ADF = 0x5144, //QD
    CBOE = 0x57, //W
    PHLX = 0x58, //X
    DIRECTEDGE = 0x59, //Y

    None = -1
}