Test 15-bit digit case for PyLong's in CI?

[skirpichev]

Feature or enhancement

Proposal:

It seems, all CI jobs run tests with --enable-big-digits=30 configure option (i.e. default). Other possible case (=15 bits) is not tested. Maybe there is some build bot, but it's not obvious which one ;-)

See #30306 (comment) Nowadays I don't see Gentoo bots and it seems that "Github Actions: Test / Windows (x86)" is using 30-bit digits, e.g. https://github.com/python/cpython/actions/runs/17363314372/job/49286316737. See #138496 (tests actions and build bots)

From prior discussion in #89732 it seems that 15-bit case does make sense for 32-bit machines, but it's not the situation right now: 30-bit is unconditional default.

Lets at least test this case in Github Actions, if it's supported!

Has this already been discussed elsewhere?

No response given

Links to previous discussion of this feature:

No response

Linked PRs

• gh-138336: find build bots, testing 15-bit case for PyLong's #138496

[vstinner]

It seems, all CI jobs run tests with --enable-big-digits=30 configure option (i.e. default). Other possible case (=15 bits) is not tested. Maybe there is some build bot, but it's not obvious which one ;-)

Maybe it's not worth it to waste CI resources on testing a configuration which is used by nobody.

From prior discussion in #89732 it seems that 15-bit case does make sense for 32-bit machines, but it's not the situation right now: 30-bit is unconditional default.

That's something else. Do you want to use 15-bit digit on 32-bit machines?

[skirpichev]

Maybe it's not worth it to waste CI resources on testing a configuration which is used by nobody.

If so, why keep this configuration supported at all?

Do you want to use 15-bit digit on 32-bit machines?

Personally I have no 32-bit machines around :-) (Well, not something that I can back to life quickly...)

Maybe nowadays this case is exotic enough to drop it?

[skirpichev]

It looks for me, that merged #30497 rather contradicts to outcome of discussion in #89732.

CC @mdickinson, @markshannon

[vstinner]

Personally I have no 32-bit machines around :-)

python.org still provides 32-bit installer for Python on Windows, even if 64-bit is now recommended.

[gpshead]

A buildbot with --enable-big-digits=15 would be a good idea.

While 15-bit digits could still be useful on non-x86 32-bit platforms that lack a 64-bit multiply accumulator such as 32-bit raspbian aarch32 userland, 32-bit raspbian does not build their python that way (it uses the default 30bit ints; i just checked the distro's 3.11 sys.int_info on my buildbot). It is still worth keeping support for fewer digits around so long as things like #101291 might desire to have less than 30 on 32-bit platforms in the future though.

[skirpichev]

Well, if we are sure that GH action is not a suitable choice, probably this issue should be moved to python/buildmaster-config repo.

One possible option with GH actions - conditionally skip new job, if change doesn't affect pre-selected files (longobject.c, some headers, marshal.c, perhaps something else like this).

32-bit raspbian does not build their python that way

I would guess, that after #30497 - downstreams just silently use 30-bit config. At least, I haven't found any counter-examples.

If 15-bit digits are useful - defaults should be rather system-dependent, not hard-wired.

[skirpichev]

@vstinner do you agree with moving this to buildmaster-config?