v * r^2 uNeg := new(Element).Negate(u) correctSignSqrt := check.Equal(u) flippedSignSqrt := check.Equal(uNeg) flippedSignSqrtI := check.Equal(t0.Multiply(uNeg, sqrtM1)) rPrime := new(Element).Multiply(rr, sqrtM1) // r_prime = SQRT_M1 * r // r = CT_SELECT(r_prime IF flipped_sign_sqrt | flipped_sign_sqrt_i ELSE r) rr.Select(rPrime, rr, flippedSignSqrt|flippedSignSqrtI) r.Absolute(rr) // Choose the nonnegative square root. return r, correctSignSqrt | flippedSignSqrt } golang.org/fips140@v1.0.0/fips...