for (i = 0; i < mlen; i++) {
workspace[0 * mlen + i] = (mlen - i <= a[0] ? a[mlen - i] : 0);
workspace[1 * mlen + i] = (mlen - i <= b[0] ? b[mlen - i] : 0);
for (i = 0; i < mlen; i++) {
workspace[0 * mlen + i] = (mlen - i <= a[0] ? a[mlen - i] : 0);
workspace[1 * mlen + i] = (mlen - i <= b[0] ? b[mlen - i] : 0);