Replace Fermat's little theorem (a^(p-2), 255 sqr + 15 mul) with the
safegcd divsteps algorithm for field element inversion. This processes
62 divsteps per batch using a 2×2 transition matrix applied to
full-precision values via 128-bit arithmetic (multiplyHigh).
12 rounds × 62 steps = 744 total divsteps (≥741 needed for 256 bits).
Uses 5×62-bit signed limb representation for intermediate values and
Montgomery-style correction (precomputed p^{-1} mod 2^62) for the
modular reduction in updateDE.
The old Fermat chain is preserved as FieldP.invFermat for reference.
https://claude.ai/code/session_01BhU63WUe9AhikZxRdw3Lpg
Claude
59df3162a6