Re: [PATCH] Byte-based C locale, draft 1

[Rich Felker <dalias@libc.org>]

On Sat, Jun 06, 2015 at 05:40:07PM -0400, Rich Felker wrote:
> Attached is the first draft of a proposed byte-based C locale. The
> patch is about 400 lines but most of it is context, because it's
> basically a lot of tiny changes spread out over lots of files.
> [...]

If we go forward with this, I think I can factor it into 3 parts:

1. Add checks for MB_CUR_MAX==1 and the bytelocale support they would
   activate, and the CODEUNIT/IS_CODEUNIT macros needed for these code
   paths. This patch would be a complete nop and would not even affect
   codegen with a decent compiler since MB_CUR_MAX==4 is a constant
   right now.

2. Introduce stdio saving of active LC_CTYPE at the time of stream
   orientation (fwide) and save/restore of current locale around stdio
   ops that need it (fputwc, fgetwc, ungetwc) and iconv usage of
   multibyte functions. This patch would increase code size in a few
   places but would not change behavior.

3. Replace the constant MB_CUR_MAX macro with a runtime-variable value
   dependent on CURRENT_LOCALE->cat[LC_CTYPE]. This would actually
   activate the byte-based C locale support. locale_impl.h is actually
   already doing this, so I think I should remove that definition
   before making any changes and only bring it back if/when stage 3
   here is committed.

In principle stages 1 and 2 could be committed in either order;
they're independent. Stage 3 is also independent in what it touches,
but if it's already committed before stage 1/2, then committing stage
1 without stage 2 is a functional regression (stdio functions no
longer behave according to spec; iconv stops working in C locale).

Rich