Integer Speedparser

speedparse-int.cs

public static int Parse(string str)
{	
	unchecked
	{
		int n = 0;
		int l = str.Length - 1;
		for (int i = l, x = 1; i >= 0; i--, x *= 10)
		{
			switch (str[i])
			{
				case '0':
				break;

				case '1':
				n += x;
				break;

				case '2':
				n += 2 * x;
				break;

				case '3':
				n += 3 * x;
				break;

				case '4':
				n += 4 * x;
				break;

				case '5':
				n += 5 * x;
				break;

				case '6':
				n += 6 * x;
				break;

				case '7':
				n += 7 * x;
				break;

				case '8':
				n += 8 * x;
				break;

				case '9':
				n += 9 * x;
				break;

				default:
				if (i == 0 && str[0] == '-') return -n;
				throw new ArgumentException($"The argument {nameof(str)} is not a number.");
			}
		}
		return n;
	}
}

I didn't test if this is actually faster.