easy way to make a custom variant of a coding system?

[Miles Bader]

Hi,

I have a bunch of files which are encoded using KDDI's custom variant
of shift_jis, which adds emoji characters.

These characters are all in Unicode now too (if not in lots of fonts),
and there are handy conversion tables available[1].

Is there are an easy way to make a "derived" coding system for this?

I mean, so that I could just add a coding system "shift_jis-kddi", and
tell emacs "use the builtin shift_jis support, but also add these
additional character codes (and their unicode code points)..."

Thanks,

-miles


[1] http://www.unicode.org/Public/UNIDATA/EmojiSources.txt


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