> mod = left % right if size_a == size_b else right - 1 - (left - 1) % right

This works, Mark!  Again, the difference in performance is very subtle, but the code is more compact.


-m timeit -s "x=22331" "x//2;x//-3;x//4;x//5;x//-6;x//7;x//8;x//-99;x//100;"
with patch: 0.321          without patch: 0.633

-m timeit -s "x=22331" "x%2;x%3;x%-4;x%5;x%6;x%-7;x%8;x%99;x%-100;"
with patch: 0.224          without patch: 0.66

-m timeit "divmod(100,20);divmod(7,3);divmod(121,99);divmod(123121,123);divmod(-1000,7);divmod(23423,-111)"
with patch: 0.839          without patch: 1.07


I'm in favour of fast_divmod_2.patch for solving both this issue and issue #26315.  Serhiy, what do you think?