Good luck with an RSA sized number and GCD
Here is an example of two miniscule numbers relative to RSA.
D(t)-d E N D X A B
28 32 61 38 23 163
47 28 1 14 0 14 16
43 28 1 18 2 16 22
35 28 1 26 4 22 32
23 28 1 38 6 32 46
7 28 1 54 8 46 64
-13 28 1 74 10 64 86
-37 28 1 98 12 86 112
-65 28 1 126 14 112 142
-97 28 1 158 16 142 176
-133 28 1 194 18 176 214
-173 28 1 234 20 214 256
-217 28 1 278 22 256 302
-265 28 1 326 24 302 352
-317 28 1 378 26 352 406
-373 28 1 434 28 406 464
-433 28 1 494 30 464 526
-497 28 1 558 32 526 592
-565 28 1 626 34 592 662
-637 28 1 698 36 662 736
-713 28 1 774 38 736 814
-793 28 1 854 40 814 896
-877 28 1 938 42 896 982