Jumping from one position to other position

[Jean Louis]

All the time I have to jump from one function to other function. What
I used so far is C-SPC C-SPC to leave mark at the point and deactivate
it. Then I can jump to other places and come back with C-u SPC.

What I would like is to keep somehow automatically source position as
new mark, when I do C-u SPC at position X that I jump to position Y,
and then from Y with C-u SPC again back to X.

But Emacs does not work this way.

If anybody have better way of jumping from one place A to place B and
returning again to place A, and again to place B, let me know.