SFAFFT speeds up boolean polynomial multiplication and makes HQC arithmetic measurably less annoying across platforms.
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01 02 Note on Number-Theoretic Transforms for Implementers -- Butterflies, Twisting, Incompleteness, and Good's Trick eprint.iacr.orgA practical NTT implementers' note on butterflies, twisting, incomplete transforms, and Good's trick, with the bounds spelled out.