Spherical harmonics should be ok. Note, that there are some difference from...

Samo Penic

2011-03-19 af3bad5b0ffbe0f19b0f85519c85a385326dec03

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Original written by Dan Kroll in FORTRAN. Code was then largely adapted and commented by Miha Fosnaric-Fosni. Rewritten into C by Samo Penic-Peni, with help of Miha's extensive explanations.