C11 _Generic support in Norcroft

One of the nice new features of C11 is the introduction of _Generic expressions. It’s also a feature which some aspects of the standard library are half-expected to rely upon: tgmath.h and stdatomic.h, both of which make heavy use of generic functions.

Norcroft does have a ___select keyword (which is used by tgmath.h), which on the surface looks very similar to _Generic, but after experimenting with it for a bit I think that it’s only capable of supporting the use-case which tgmath.h is using it for (select between 3 or 9 expressions depending on what type of float argument is provided). tgmath.h hails from C99, whereas _Generic and stdatomic.h are C11, so it’s not too surprising that ___select was implemented as a special case just to get tgmath working.

Unfortunately, without _Generic (or similar), I don’t think it’s possible to provide a stdatomic.h implementation for Norcroft.

Doesn’t Norcroft still use CFront? If so it’s not really appropriate for modern use; elsewhere there have been “proper” C++ compilers since 1992 or earlier…

not really appropriate for modern use

Who’s writing C++ for the RISC OS ROM?…

Whoops — saw "C11” and mistook it for C++11. Sorry!

elsewhere there have been “proper” C++ compilers since 1992 or earlier…

Up until about 1992, there was only CFront and a few experimental C++ compilers. Starting in 1992, the first few “true” C++ compilers which approached production readyness became available (DEC IIRC, and Microsoft).

Soon after that, we got a port of GCC 2.3.3 (g++) and Easy C++. Probably 1994/1995?

C++ got an official standard as late as 1998, until then the world of C++ compilers was quite hit-and-miss – I remember working with an IBM C++ compiler on a PowerPC-based AIX multicomputer with three CPUs, and it was a nightmare of bugs and a wild mixture of “features” (exceptions somehow-supported-but-not-really, templates supported-but-only-simple-cases, STL-we-have-our-own-great-implementation-here-but-don’t-expect-it-to-work). And that was 1998.

I was at UCL in 1987 which was one of the first UK universities to offer C++ as part of a computer science course. We used CFront on a Pyramid mini and then Sun 3/50 workstations, a year later Acorn C/C++ was released with the very same version of CFront. This was handy as I was able to do my projects on my own Archimedes 310, rather than fight over the limited number of Suns swapping their 2 or 4 MB of RAM over the 10Base2 Ethernet. Of course I had to make both Wimp and X Windows front ends, but it was still quicker to develop that way.

Unfortunately Acorn’s CFront never gained any new functionality, and by 1989 native C++ compilers had left it for dead. It’s now so primitive, I think I only have one significant program which still compiles on it. I ended up having to downgrade to plain old C to write all my RISC OS code in the 90s. Even when a viable version of GNU G++ came along, Norcroft C compiled so much quicker I stuck with that on RISC OS, while continuing with C++ on Linux and Windows.

Back on the topic of C, while reading up on the deficiencies in C11’s thread specification, I’ve also discovered that the _Generic specification was also a bit vague, leading to some interoperability issues. So anyone looking to implement _Generic should look at the C18 spec (or newer), where the spec has been tightened up a bit.

The first PC compiler was Zortech C++, back in 1988. By 1992, Borland’s Turbo C++ was available. Microsoft C++ came out in the same year; Visual C++ early in 1993. All of these were true compilers.

I remember Digital’s C++ compiler, cxx. It was used at the university where I worked. It would compile and link a program with no main function. In this case it would simply run the first function in the file instead.

DDE30 contains _Generic support (along with assorted other C18 bits). Hurrah!

Many thanks, ROOL.

Now I guess I should try and finish off that stdatomic implementation I was working on.

Got mine too Jeffrey, just in time for the weekend!

almost time to play with your lib, SIMD math and DDE30… another epic weekend kindly ran on RISC OS :D

Many thanks ROOL!

Many thanks ROOL!

You’re welcome!