stgex2(3) on Linux
The text 64accd9d6aea, as Debian 4.0 (Etch), Debian 3.1 (Sarge) shipped it.
swap adjacent diagonal blocks (A11, B11) and (A22, B22) of size 1-by-1 or 2-by-2 in an upper (quasi) triangular matrix pair (A, B) by an orthogonal equivalence transformation