Fix type_traits_test on platforms where char is unsigned

[singhc7]

Summary

Fixes the static_assert in test/unittest/type_traits_test.cpp that assumes char is signed. On platforms where char is unsigned by default (e.g. aarch64-linux, ppc64), to_unsigned_t<char> resolves to char rather than unsigned char, and the original assertion fails to compile.

Guards the assertion with CHAR_MIN < 0 so the correct relationship is checked on each platform, and adds #include <climits> for the macro.

The library itself is correct on these platforms — only this test assertion was platform-unsafe.

Changes

• test/unittest/type_traits_test.cpp: add #include <climits>, guard the to_unsigned_t<char> assertion with CHAR_MIN < 0.

Verification

Built and ran the full test suite on aarch64-linux (where the failure originally manifested):

100% tests passed, 0 tests failed out of 126

The signed-char branch is the original upstream assertion, unchanged in behavior on platforms where char is signed.

Related

Closes #191

[singhc7]

Hi @yosupo06!

Sorry to ping directly — I opened a small PR (#192) that fixes type_traits_test.cpp on platforms where char is unsigned by default (aarch64-linux, ppc64, etc.). The library itself works fine on these platforms; only one static_assert was making a signedness assumption.

Whenever you have a moment, would appreciate a look. Happy to make any changes if you'd prefer a different approach. Thanks for maintaining ac-library!