> On 19. Sep 2021, at 19:41, Malte Voos <ma...@malvo.org> wrote: > > Hi! > > Thanks for the explanation. This may be a stupid question, but why not > just use the bswap_* definitions from the libc?
I do not know why it is/was done in this way, possibly because there are platforms that use gcc but not glibc. Maybe historically for win32 support. > In glibc's case, bswap_* > becomes __bswap_* (which is still not a compiler builtin, but a glibc > internal name), which in turn becomes __builtin_bswap* if the GCC is > recent enough. [1] In bionic's case, bswap_* always becomes > __builtin_bswap* [2] [3]. Only musl doesn't use the builtins [4]. In my > view, we have three options here: > > * Use the bswap_* definitions provided by the libc and accept that some > might not use compiler builtins > * Use __builtin_bswap*, which is supported by both non-ancient GCC [5] > and Clang [6] > * Keep rolling our own bswap compatibility layer to support obscure > compilers. In this case, I'd suggest that we check if __builtin_bswap* > is available, and if not, use the manual implementations we already > have. > > I don't think sticking with __bswap* is a good idea, since it is > basically an implementation detail of glibc and musl, not a compiler > builtin. I changed it to this for now: https://git.gnunet.org/gnunet.git/commit/?id=83c0efff026598098addfabdf72698d5d13b7b48 May break *BSDs and obscure byteswap.h. It uses and libc/OS bytesswap.h now if present, otherwise the fallback implementation. BR > > -malvo > > [1] > https://sourceware.org/git/?p=glibc.git;a=blob;f=string/byteswap.h;h=e9da7a4f68a095866966fafcaf09456910f40018;hb=HEAD > [2] > https://android.googlesource.com/platform/bionic/+/master/libc/include/byteswap.h > [3] > https://android.googlesource.com/platform/bionic/+/824f914/libc/include/sys/endian.h > [4] https://git.musl-libc.org/cgit/musl/tree/include/byteswap.h > [5] https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html > [6] > https://github.com/llvm/llvm-project/blob/2ca637c9769ff50e94ace3083075a97b50d147f0/clang/include/clang/Basic/Builtins.def#L514
signature.asc
Description: Message signed with OpenPGP
