Bug report

Bug description:

As per C11 DR#471 (accepted for C17), ctanh (0 + i NaN) and ctanh (0 + i Inf) should return 0 + i NaN (with "invalid" exception in the second case). Currently, real part is nan.

This has corresponding implications for ctan(z), as its errors and special cases are handled as if the operation is implemented by -i*ctanh(i*z).

See glibc patch: https://sourceware.org/git/?p=glibc.git;a=commitdiff;h=d15e83c5f5231d971472b5ffc9219d54056ca0f1

CPython versions tested on:

CPython main branch

Operating systems tested on:

No response

Linked PRs

• gh-122637: fix tanh(±0+infj) and tanh(±0+nanj) to return ±0+nanj #122638