gf_mul
nxxy = gf_mul(gf_mul(nx, nx), ny);
nxyy = gf_mul(gf_mul(nx, ny), ny);
nyyz = gf_mul(gf_mul(ny, nz), ny);
nyzz = gf_mul(nzz, ny);
xd = gf_mul(nxx, ny) ^ gf_mul(nx, nyy) ^ nyyz ^
gf_mul(nxx, nz) ^ gf_mul(nzz, nx) ^ nyzz;
coeff[MUL_PQR_YP] = gf_mul(nz, yd);
vdev_raidz_mul_lt[c][i] = gf_mul(c, i);