gh-104399: Use newer libtommath APIs when necessary

[chrstphrchvz]

• Issue: Tkinter uses deprecated functions mp_to_unsigned_bin_n() and mp_unsigned_bin_size() #104399

[chrstphrchvz]

As with #103842, this requires knowing whether Tcl was built with TCL_WITH_EXTERNAL_TOMMATH defined, which is something not currently available via pkg-config.

[gpshead]

general thought: We could use a buildbot with bleeding edge versions of tcl/tk

[serhiy-storchaka]

The new API is available since 8.6.10. Would not be better to use it as soon as it is available? Potentially it can support larger integers.

Suggested change

	#if defined(TCL_WITH_EXTERNAL_TOMMATH) || (TCL_MAJOR_VERSION >= 9)
	#if defined(TCL_WITH_EXTERNAL_TOMMATH) || (TK_HEX_VERSION >= 0x0806020a)

[chrstphrchvz]

I am not familiar with libtommath APIs nor aware what the exact limits are, but I would think that Tcl is more likely to be the limiting factor anyway, as even the deprecated libtommath functions can handle numbers exceeding what Tcl < 9 can usefully convert to and from (due to various 2**31-1 size limitations on strings, etc.).

Given how Tkinter requires the Tcl version but not the patchlevel to match at compile time and runtime (#104399 (comment)), it should be fine to enable the new functions on Tcl 8.7; this would also allow not having to check for TCL_WITH_EXTERNAL_TOMMATH in this case (although it still has to be checked for #103842).

[serhiy-storchaka]

Agree.

[miss-islington]

Thanks @chrstphrchvz for the PR, and @serhiy-storchaka for merging it 🌮🎉.. I'm working now to backport this PR to: 3.11, 3.12.
🐍🍒⛏🤖

[bedevere-bot]

GH-105343 is a backport of this pull request to the 3.12 branch.

[bedevere-bot]

GH-105344 is a backport of this pull request to the 3.11 branch.