Is that this algorithm impressed by a public paper?
Any reference could be useful, as I am unable
to comply with motive in regards to the code itself.
I’m not positive about “papers”, however kind of formal articles on modular multiplication in actual fact abound: certainly, the implementation in query “merely” leverages identified properties of modular arithmetic.
As to the specifics, the next is the hyperlink to a submit about an older and considerably less complicated model of secp256k1_fe_mul_inner than the present one, however it could be sufficient to help additional exploration/reverse-engineering:
That article additionally incorporates a hyperlink to the related modular arithmetic, in a pleasant and compact sequence of slides, which I’ll repost right here:
(There may very well be some added worth in explaining the current implementation of secp256k1_fe_mul_inner, because it provides few extra optimizations on high of the fundamental modular arithmetic. However I believe that will require a degree of element and ritual that’s effectively past the scope of the current query.)
