Path: csiph.com!eternal-september.org!reader02.eternal-september.org!.POSTED!not-for-mail From: Tim Rentsch Newsgroups: comp.lang.c Subject: Re: naked switches Date: Sun, 11 Jul 2021 00:57:08 -0700 Organization: A noiseless patient Spider Lines: 52 Message-ID: <861r858eqz.fsf@linuxsc.com> References: <06a0049a-2d7d-40f0-899a-fb35c9a15d5fn@googlegroups.com> <8735sp8cbm.fsf@nosuchdomain.example.com> <255c09e7-2365-4983-ad4d-3bfc83cf04e7n@googlegroups.com> <31342574-cb69-4ad6-8576-387dcf9caf70n@googlegroups.com> <7e094b82-01be-4d7f-9793-4eeda725ca0en@googlegroups.com> <20210708103653.702@kylheku.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Injection-Info: reader02.eternal-september.org; posting-host="52e1adecb53146628fb5ee5c083fc413"; logging-data="8554"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1/boOOC7cCeodrC2rpE/rvVxiLa3c6AGN4=" User-Agent: Gnus/5.11 (Gnus v5.11) Emacs/22.4 (gnu/linux) Cancel-Lock: sha1:+lCvtHN4CXnbyMYIrK0FBl5sgiU= sha1:xyePTU6SmsfDOAlk4AbJ6726k4k= Xref: csiph.com comp.lang.c:161869 Kaz Kylheku <563-365-8930@kylheku.com> writes: > On 2021-07-08, Robert Finch wrote: > >>> You wrote that you "have been working on a C/C++ like compiler" - do you >>> mean you have been /using/ such a compiler, or you have been /writing/ >>> such a compiler? >> >> I have been using it for simple demos, actually running the compiled >> code sometime. It has been revamped for several different custom >> processors, but is still a work in progress. >> >>> As I mentioned earlier, I think a "naked switch" like this is a terrible >>> idea. It is not something I have seen on other compilers, and I've used >>> quite a large number over the years for far smaller and slower devices >>> than you are describing here. >> >> It is a bad idea in terms of allowing program crashes. But then >> there are naked functions. >> >> CC64 supports a number of ?features? not found in standard C. But I >> call it a ?C? like compiler because it can compile most C code >> without changes. I used it to compile the standard C library. >> Stills lots of bugs in the compiler though. >> >> One feature I like is the ability to manipulate bit slices. >> >> int a, b; >> >> a = b[10:1]; >> >> Sets a equal to bits 1 to 10 of b. A bit slice can be distinguished >> from an array index by the colon. Compiles painlessly directly to >> field manipulation instructions and gets rid of code like: a = (b >> >> 1) & 0x3ff; > > A macro can do this: > > a = BIT(b,10,1); > > and works everywhere. What you need is a typeof extension to make it > work with different integer types while retaining efficiency, otherwise > you're looking at making it assume 64 bit, or saddling it with a type > name argument. [... and later _Generic is mentioned.] No typeof is needed, nor _Generic, nor type name argument, nor forcing a width of 64 bits, to define a macro that produces an "and" of the appropriate size with a compile-time constant (as evidenced by both gcc and clang with -O0). Just straight C90. (I'll try to post a followup in a day or two, if necessary, to show how. But I expect someone here will get it before then.)