Consolidate byte-swapping paths to avoid undefined behavior [rt.cpan.org #130493]

[toddr]

Migrated from rt.cpan.org#130493 (status was 'new')

Requestors:

• [email protected]

From [email protected] on 2019-09-11 17:15:22
:

Pull request containing fix is at https://github.com/gisle/digest-md5/pull/16

The code guarded by #ifndef U32_ALIGNMENT_REQUIRED attempts to optimize
byte-swapping by doing unaligned loads, but accessing data through
unaligned pointers is undefined behavior in C. Moreover, compilers are
more than capable of recognizing these open-coded byte-swap patterns and
emitting a bswap instruction, or an unaligned load instruction, or a
combined load, etc. There's no need for multiple paths to attain the
desired result.

See https://rt.perl.org/Ticket/Display.html?id=133495

[toddr]

which became Perl/perl5#16680

[toddr]

and also Perl/perl5#17244

[toddr]

@mattst88 at this point I'm unclear if anything is needed here or if the problem was with blead not Digest-MD5?

[mattst88]

I think there is nothing else to do here for the dual-life version. In fact, Digest-MD5 actually became dual-life because it was impossible to get fixes into the dead Digest-MD5 project. The solution was to make it dual-life and to fix it there.

[toddr]

Digest-MD5 is still in cpan/ and this is the place to fix stuff.

[mattst88]

Okay, good luck trying. I got an enormous amount of run-around trying to do exactly that before the original Digest-MD5 maintainer finally responded to a private email and told me he wasn't maintaining it anymore.

[toddr]

It is being maintained here by me. I am looking at Perl/perl5@ee9ac1c now and trying to determine if it is backward compatible with previous perls.

[mattst88]

Yes, I believe it is backwards compatible.