Subject: Re: bug#40407: [PATCH] slow ENCODE_FILE and DECODE_FILE

From: Eli Zaretskii <[email-masked]>
Date: Mon, 06 Apr 2020 19:33:16 +0300

> From: Mattias Engdegård <[email-masked]>
> Date: Mon, 6 Apr 2020 17:56:27 +0200
> Cc: OGAWA Hirofumi <[email-masked]>,
>         Kenichi Handa <[email-masked]>, [email-masked]
> 
> > Kenichi, why was coding-type of UTF-7 systems set to 'utf-8'?
> > Wouldn't it be better to set it to 'utf-16'?  Or is there some
> > subtlety here that we should be aware of?  Do you have any comments on
> > the patch below?
> 
> There is no reason why utf-7[-imap] should have utf-8 as coding-type, is there?

I think it might be just some convenience thing: utf-7 and utf-8 have
something in common that made it convenient to treat them the same in
the internal routines.  Or maybe it's just an accident.

> utf-16 is definitely wrong (utf-7* are encoded in ASCII).

Why do you think the ASCII encoding contradicts the utf-16
coding-type?

> What about the patch below instead?

I don't think 'charset' is the right type for this encoding (any
reason why you've chosen it?), but I will let Handa-san comment.
Defining coding-systems is a black art which I don't think I ever
mastered.