On 15/10/2024 16:50, Jeffrey Walton wrote:
On Tue, Oct 15, 2024 at 10:59 AM Pádraig Brady <p...@draigbrady.com> wrote:
On 15/10/2024 12:58, Sam Russell wrote:
I'm happy with the slice-by-8 code I have
<https://github.com/samrussell/gnulib/blob/slice_by_8/lib/crc.c
<https://github.com/samrussell/gnulib/blob/slice_by_8/lib/crc.c>> but the
cksum_pclmul implementation is quite detailed so it would be useful if we could relicense
that for gnulib.
Sounds good re slice-by-8.
Re pclmul in gnulib, I don't want to add stop energy, but it's worth
considering:
In general gnulib focuses on portable routines, so for example leaves
platform specific crypto optimizations to libcrypto, only providing fallback
cross platform implementations where needed.
In coreutils we needed to build the pclmul code as a separate library
so that with autotools it can be portably built with separate -mavx etc. flags.
There are both build time and runtime guards around the pclmul code.
I believe the correct option is -mpclmul, not -mavx. If the source
files are building with -mavx, then it is due to luck. Also see
<https://gcc.gnu.org/onlinedocs/gcc/x86-Options.html>.
Every now and again, I come across a weird combination of ISAs. I
actually encountered a low-end cpu that included SSE4.1+AES, but
lacked PCLMUL. It was on a cheap HP machine. I also encountered GCC on
MacPorts that could build a source file with AES, but not PCLMUL.
Right, sorry for being imprecise.
coreutils builds this code with -mavx -mpclmul
cheers,
Pádraig
