% -*- mode: tex -*-
%-
% Copyright © 2018
%	mirabilos <t.glaser@tarent.de>
%
% Provided that these terms and disclaimer and all copyright notices
% are retained or reproduced in an accompanying document, permission
% is granted to deal in this work without restriction, including un‐
% limited rights to use, publicly perform, distribute, sell, modify,
% merge, give away, or sublicence.
%
% This work is provided “AS IS” and WITHOUT WARRANTY of any kind, to
% the utmost extent permitted by applicable law, neither express nor
% implied; without malicious intent or gross negligence. In no event
% may a licensor, author or contributor be held liable for indirect,
% direct, other damage, loss, or other issues arising in any way out
% of dealing in the work, even if advised of the possibility of such
% damage or existence of a defect, except proven that it results out
% of said person’s immediate fault when using the work as intended.
%
% 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%
}%
