OR operation can't calculate original value?

Question

a|b=c

knowing a and c, how to calculate b

For example:

0011 | b = 0111

Knowing a = 0011 and c = 0111, how to figure out b to be 0101

Your problem is under-determined. It can exist several values... The most trivial answer is if a|b=c for b unknown then b=c is a valid answer... — Jean-Baptiste Yunès, May 04 '18 at 08:15
You are confusing or `|` and xor `^`, or is under-determined. However, with xor the solution would be [What is inverse function to XOR?](https://stackoverflow.com/questions/14279866/what-is-inverse-function-to-xor) — Lanting, May 04 '18 at 08:29

score 0 · Accepted Answer · answered May 04 '18 at 08:22

0

There will be more than one correct answer.

For simplicity consider the trivial example: 1|0 = 1 i.e. a=1, b=0 and c=1. In this case, b can also be 1.

So given that the bit in a is 1, we won't be able to know for sure whether the bit in b is 0 or 1.

answered May 04 '18 at 08:22

score 0 · Answer 2 · answered May 04 '18 at 09:31

In some logics there is also a "value" for unknown X

So if you want to get bfrom a|b=c => 0011 | b = 0111 the in my mind nicest answer would be 01XX

Everything that is:

2 Answers2