C2x was finalized at the June 2023 WG14 meeting. The DIS is out for
balloting and the comment period for that closes later this year/early
next year. While that does leave an opportunity for more changes to the
standard during the DIS ballot resolution process, only editorial
changes are anticipated and as a result, the C committee considers C2x
to be final. The committee took a straw poll on what we'd prefer the
informal name of the standard be, and we decided it should be called
C23 regardless of what year ISO publishes it.
However, because the final publication is not out, this patch does not
add the language standard alias for the -std=iso9899:<year> spelling of
the standard mode; that will be added once ISO finally publishes the
document and the year chosen will match the publication date.
This also changes the value of __STDC_VERSION__ from the placeholder
value 202000L to the final value 202311L.
Subsequent patches will start renaming things from c2x to c23, cleaning
up documentation, etc.
Differential Revision: https://reviews.llvm.org/D157606
Part of the _BitInt feature in C2x
(http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2763.pdf) is a new
macro in limits.h named BITINT_MAXWIDTH that can be used to determine
the maximum width of a bit-precise integer type. This macro must expand
to a value that is at least as large as ULLONG_WIDTH.
This adds an implementation-defined macro named __BITINT_MAXWIDTH__ to
specify that value, which is used by limits.h for the standard macro.
This also limits the maximum bit width to 128 bits because backends do
not currently support all mathematical operations (such as division) on
wider types yet. This maximum is expected to be increased in the future.
This completes the implementation of
WG14 N2412 (http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2412.pdf),
which standardizes C on a twos complement representation for integer
types. The only work that remained there was to define the correct
macros in the standard headers, which this patch does.
