unicodedomino_kernel_better_decode.def

% -*- mode: tex -*-
%-
% See unicodedomino.sty for copyright and licence terms. Furthermore
% this file is dual-licenced under the LPPL version 1.3c or later.
%-
% Improved Unicode decoding using the fixed-up checkseq code.

% override stock function, calling safer decode below
\gdef\decode@UTFviii#1\relax{%
 \the\numexpr(\UTFviii@decode0:#1\relax)%
}%

% safer decode, returns 0x1FFFFF for illegal sequences
\gdef\UTFviii@decode#1\relax{%
 \if\relax\expandafter\UTFviii@checkseq\string#1\empty\relax%
  \UTFviii@dec@lead#1\relax%
 \else%
  2097151%
 \fi%
}%

\gdef\UTFviii@dec@lead#1:#2#3\relax{%
 % we know #2 is in 00..7F, C2..F4
 \ifnum`#2<"80 %
  `#2%
 \else%
  \ifnum`#2<"E0 %
   (`#2-"C0%
  \else%
   \ifnum`#2<"F0 %
    ((`#2-"E0%
   \else%
    (((`#2-"F0%
   \fi%
  \fi%
  \UTFviii@dec@trail#3\relax%
 \fi%
}%

\gdef\UTFviii@dec@trail#1#2\relax{%
 )*64+(`#1-"80)%
 \ifx\relax#2\else\UTFviii@dec@trail#2\relax\fi%
}%