Re^2: Encoding: my custom encoding fails on one character but works for everything else?!

[herveus]

Howdy!

Thanks for those findings! There is one other potential case (at present) where there could be a single character between {}, but at present, {i} is the only one I'm using.

I've long had a module that handled this conversion, but it was a standalone thing, not integrated into the Encode system. A friend wanted to be able to systematically recode file and directory names between UTF-8 and Daud. He found 'convmv' which turns out to be a Perl program that uses Encode to do the heavy lifting. That motivated me to once again try to make Daud work in the Encode framework, leading here.

[graff]

I tried a bunch of other variations on the same sort of theme. I have only taken a quick glance at the C code created by enc2xs (and the differences in C code resulting from different variations of ucm), and I still don't understand exactly what's wrong with this process. But based on what I've seen, the symptom appears to be something like this:

For any mapping that includes strings of 3 or more "non-unicode" bytes equating to unicode code points, the arrangement of definitions in the ucm file should have at least one of the 3-byte strings before any of the longer string definitions. That is:

...
<Uhhhh>  \xhh\xhh\xhh  |0   # first mention of any multi-byte mapping
...
<Uhhhh>  \xhh\xhh\xhh\xhh |0
...

The above arrangement will work, whereas the arrangement below will have the problem as described in the OP:

...
<Uhhhh>  \xhh\xhh\xhh\xhh |0  # first mention of any multi-byte mappin
+g
...
<Uhhhh>  \xhh\xhh\xhh  |0
...

(updated to remove spurious spaces)

Bear in mind that the ucm definitions don't need to be in unicode code-point order -- enc2xs doesn't care about the ordering (except when it comes to triggering this one strange little bug).

It probably applies to any mapping involving 2-byte strings as well, (that would seem logical), but I haven't tested that. In a nutshell, try ordering your definitions with respect to how long the encoded byte strings are, or at least put one instance of a 3-byte string mapping ahead of all instances of 4-byte mappings.

(So it was just "coincidental" that I chose q-mark for the initial attempt in my first reply -- it only worked because it just happened to be conventionally placed above the accented letters.)

[herveus]

Howdy!

Hmmm... Thank you for that insight. I'll look into that nuance tonight as well.