dct_II_inplace(buf, hsize, step * 2, tab, perm_tab);
dct_II_inplace(&mut buf[step..], hsize, step * 2, tab, perm_tab);
for i in 0..(size >> 2) {
dct_II_inplace(buf, hsize, step * 2, tab, perm_tab);
dct_II_inplace(&mut buf[step..], hsize, step * 2, tab, perm_tab);
for i in 0..(size >> 2) {