update boost-math and fix std::ellint_2

[fsb4000]

Fixes #3076 / VSO-1600625 / AB#1600625 / DevCom-10133797

I updated boost-math submodule to 1.80, https://github.com/boostorg/math/releases/tag/boost-1.80.0

I copied assert_close from:

STL/tests/std/tests/Dev09_158181_tr1_unordered_meow_swap/test.cpp

Lines 22 to 24 in f9697fc

	void assert_close(const float f, const float g) {
	assert(abs(f - g) < 0.01f);
	}

Do we need to update something else like these hashes #2598 ?

Am I correct that this change is an affects redist change and it is blocked for now?

[StephanTLavavej]

I believe we should update the hash in cgmanifest.json, yes.

More importantly, we'll need to update the version of Boost.Math used in the MSVC-internal build, otherwise this fix won't "take effect" for the shipping product. Currently it's using a patched copy of Boost 1.66.0 (the patches are all upstreamed now). I believe it should be fairly simple to drop that and switch to standalone Boost.Math via submodule (with the greatest difficulty being MSBuild), except for the question of test coverage. Currently we have one test for Special Math that Casey prepared by deriving from Boost's tests (and it is internal-only because we haven't had time to deal with it; nothing was fundamentally blocking it from moving to GitHub though). That test will fail with the newer version of Boost.Math due to various implementation changes, probably all intentional.

I don't believe we have a tracking issue for this, but IIRC Casey mentioned that an exhaustive test is probably not necessary. All we would need is a test that exercises every function for a few example data points, to verify that nothing is horribly messed up. I believe the only special focus such a test would need is for the extra logic we have to deal with divergence between the Standard and Boost's requirements (this is clearly commented in the source code).

Would you be interested in adding such test coverage? I think we could find a maintainer to make the MSBuild changes and complete the upgrade.

[fsb4000]

Would you be interested in adding such test coverage? I think we could find a maintainer to make the MSBuild changes and complete the upgrade.

Yes, I can add couple tests for every special functions.

[fsb4000]

I believe the only special focus such a test would need is for the extra logic we have to deal with divergence between the Standard and Boost's requirements (this is clearly commented in the source code).

Yes, I saw that, but I didn't add yet. I will add them tomorrow.

and I will remove void assert_close from LWG3234_math_special_overloads/test.cpp

[fsb4000]

ready for a review

[strega-nil-ms]

Made the test changes I wanted to see; thanks for the work you've done!

[StephanTLavavej]

The new test is failing for x86 only:

Assertion failed: isclose(beta(2.0, 3.0), 0.08333'3333'3333'3333'3333),
file D:\a\_work\1\s\tests\std\tests\P0226R1_math_special_functions\test.cpp, line 104

I haven't investigated, but perhaps we need an extra ULP?

[strega-nil-ms]

Yeah, I investigated - it looks like an issue with the non-SSE2 x86 implementation of Lanczos::lanczos_sum_expG_scaled being less accurate than the SSE2 implementation. It results in a 2 ULP difference from the actual answer.

[AreaZR]

Any update on this?

[fsb4000]

I think it will be merged in VS 2022 17.6 Preview 2: https://github.com/microsoft/STL/wiki/Changelog#vc-redist-lockdown

[CaseyCarter]

Just a couple of minor issues that I'll push fixes for.

[CaseyCarter]

We discussed in the maintainer meeting this week that we think it's fine to merge this even with the redist currently locked. The special math functions aren't the most heavily used, so we are willing to tell people that the workaround for GH-3076 is to link statically until 17.6 preview 2 unlocks the redist and we can update the DLLs.

[StephanTLavavej]

Thanks! Found a few missing tests, I'll validate and push changes.

[StephanTLavavej]

@CaseyCarter @strega-nil-ms I pushed minor changes after you approved, to remove an unnecessary static and add meowf/meowl coverage.

I also pushed a conflict-free merge with main and verified that there's no clang-format 15 impact.

[StephanTLavavej]

I'm mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed.

[StephanTLavavej]

Thanks for fixing this bug and adding Special Math test coverage, so that we can now use Boost 1.80.0 to build the official STL DLLs! 😻 🎉 🧮