QuadDtype Wishlist

[juntyr]

This is my personal list of patches around numpy-quaddtype that I currently have in my own project that I'd like to fix upstream - I will work on most of them myself and will reach out if I need help with some:

Constants

• expose precision: could just be hardcoded to 33, the precision of np.float128 on a platform with native float128 support

Ufuncs

• sign ufunc: implemented in Implement sign, sigbit, and copysign ufuncs and extend unary op tests #118
• sinh, cosh, tanh, asinh, acosh, atanh ufuncs: supported by SLEEF
• fix mod ufunc: tracked in SleefQuadPrecision np.mod ufunc gives unexpected results #113
• isnan, isinf, isfinite ufuncs: implemented in Implement isfinite, isinf, isnan ufuncs #121
• nextafter and spacing ufuncs: probably possible

Dtype

• support np.issubdtype(dtype, np.floating)
• finfo support: tracked in SleefQuadPrecDType does not work with np.finfo #112, ENH: np.finfo support for Numpy User DTypes numpy#27231, ENH: Uniform interface for accessing minimum or maximum value of a dtype numpy#27785, not yet possible
• nan_to_num ufunc: depends on finfo support
• custom dtype kind character, not '\0', tracked in SleefQuadPrecDType kind, char, num #110, not yet possible

Binary

• cast to an equal-sized unsigned integer type

[ngoldbaum]

It'd also be nice to have proper API docs for the Python API generated by e.g. Sphinx. We should also make sure there are docstrings (preferably doctested in CI) on the full public Python API.

[juntyr]

Once we get to writing documentation, we should also document the guaranteed rounding error in ULPs for each operation - thankfully SLEEF documents it fully - since people who need float128, myself included, then likely also care about rounding errors