SSHT performs fast and exact spin spherical harmonic transforms; functionality is also provided to perform fast and exact adjoint transforms, forward and inverse transforms, and spherical harmonic transforms for a number of alternative sampling schemes. The code can interface with DUCC (ascl:2008.023) and use it as a backend for spherical harmonic transforms and rotations.
https://ui.adsabs.harvard.edu/abs/2011ITSP...59.5876M and a link to https://github.com/astro-informatics/ssht; if using our fast adjoint algorithms, then please also cite https://ui.adsabs.harvard.edu/abs/2013ITIP...22.2275M