* <https://i.stack.imgur.com/QSLKY.png>
* <https://stackoverflow.com/questions/27971757/big-integer-addition-code>
`((P|G)+G)^P`
+* <https://en.m.wikipedia.org/wiki/Carry-lookahead_adder>
+
+ P = (A | B) & Ci
+ G = (A & B)
+
+Stackoverflow algorithm `((P|G)+G)^P` works on the cumulated bits of P and G from associated vector units (P and G are integers here). The result of the algorithm is the new carry-in which already includes ripple, one bit of carry per element.
+
+
two versions: scalar int version and CR based version.