Crazy Parsing

gistfile1.cs

private static unsafe int ParseFast(string data)
{
    int count = 0, valid = 0, pos, stop, temp;
    byte[] buffer = new byte[ushort.MaxValue];

    const byte Zero = (byte) '0';
    const byte Nine = (byte) '9';
    const byte Dot = (byte)'.';
    const byte Space = (byte)' ';
    const byte Tab = (byte) '\t';
    const byte Line = (byte) '\n';

    fixed (byte *ptr = buffer)
    using (Stream reader = File.OpenRead(data))
    {
        while (0 != (temp = reader.Read(buffer, valid, buffer.Length - valid)))
        {
            valid += temp;
            pos = 0;
            stop = Math.Min(buffer.Length - 1024, valid);
            while (pos < stop)
            {
                double d;
                long a = 0, b = 0;
                while (pos < valid && ptr[pos] >= Zero && ptr[pos] <= Nine)
                    a = a*10 + (ptr[pos++] - Zero);
                if (ptr[pos] == Dot)
                {
                    pos++;
                    long div = 1;
                    while (pos < valid && ptr[pos] >= Zero && ptr[pos] <= Nine)
                    {
                        b += b*10 + (ptr[pos++] - Zero);
                        div *= 10;
                    }
                    d = a + ((double) b)/div;
                }
                else
                    d = a;

                while (pos < valid && (ptr[pos] == Space || ptr[pos] == Tab))
                    pos++;

                int i = 0;
                while (pos < valid && ptr[pos] >= Zero && ptr[pos] <= Nine)
                    i = i*10 + (ptr[pos++] - Zero);

                DoSomething(d, i);

                while (pos < stop && ptr[pos] != Line)
                    pos++;
                while (pos < stop && !(ptr[pos] >= Zero && ptr[pos] <= Nine))
                    pos++;
            }

            if (pos < valid)
                Buffer.BlockCopy(buffer, pos, buffer, 0, valid - pos);
            valid -= pos;
        }
    }
    return count;
}