prep_zero_mask
adata = prep_zero_mask(a, adata, &constants);
adata = prep_zero_mask(a, adata, &constants);
bdata = prep_zero_mask(b, bdata, &constants);
adata = prep_zero_mask(a, adata, &constants);
bdata = prep_zero_mask(b, bdata, &constants);
data = prep_zero_mask(c, data, &constants);
data = prep_zero_mask(c, data, &constants);
data = prep_zero_mask(c, data, &constants);