q12
for (i = 0; i < p; ++i) R[i] = r[i] + q12;
for (i = 0; i < p; ++i) r[i] = ((Fq)R[i]) - q12;
for (i = 0; i < p; ++i) R[i] = ((r[i] + q12) * 10923) >> 15;
for (i = 0; i < p; ++i) r[i] = R[i] * 3 - q12;