(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

At my company we calculate a product's serial number from a MAC address provided with the unit. One of the equations is done with a bitwise AND operation of two integers. I have tried to run that equation backwards but with no result.

Variables and data:

V = The source value to do the bitwise AND operation with

C = A known constant to use in the bitwise AND operation

S = Result of bitwise AND operation

Let say: V = 10, C = 6

2. Relevant equations

The equation forward is: V & C = S => 10 & 6 = 2

In binary:

1010 = 10

0110 = 6

-----

0010 = 2

Now I just want to reverse that process and calculate 10 from 6 and 2 in some way.

Don't try with: C + 2S (6 + (2*2)) works just in this case.

3. The attempt at a solution

I tried the opposite way by changing V for S:

2 & 6 = 2

In binary:

0010 = 2

0110 = 6

-----

0010 = 2

The problem occurs when one of the bits in the V is 1 and the equivalent bit in C is 0. The bit in S will then be 0 and V's bit can never return to 1.

Any suggestions?

/Mc_Topaz

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# Bitwise AND operation backwards

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