return fieldMontgomeryMul(fieldElement(x), RR) } // fieldFromMontgomery converts a value a in Montgomery form back to // standard representation. func fieldFromMontgomery(a fieldElement) uint32 { // (a * R) * 1 * R⁻¹ ≡ a (mod q) return uint32(fieldMontgomeryReduc(uint64(a))) } // fieldCenteredMod returns r mod± q, the value r reduced to the range // [−(q−1)/2, (q−1)/2]. func fieldCenteredMod(r fieldElement) int32 { x := int32(fieldFromMontgomery(r)) // x <= q / 2 ? x : x - q return constantTimeSelectLe(x,...