Re: Reducing the cost of autodecoding

[Uplink_Coder via Digitalmars-d]

On Saturday, 15 October 2016 at 19:07:50 UTC, Patrick Schluter 
wrote:
At least with that lookup table below, you can detect isolated 
continuation bytes (192 and 193) and invalid codes (above 244).

__gshared static immutable ubyte[] charWidthTab = [
            1, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
            2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
            3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
            4, 4, 4, 4, 4, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1
];
length 5 and 6 need not to be tested specifically for your goto.

If you use 0 instead of 1 the length check will suffice for 
throwing on invalid.