XOR

Can be used at [interview]

https://xania.org/202512/01-xor-eax-eax
- encryption part of the code, or some kind of sprite routine
- mov eax, 0x0 takes 5 steps
- xor eax, eax sets the eax register to 0
- Used everywhere in the linux kernel
That XOR Trick
- You are given an array of n - 1 integers which are in the range between 1 and n. All numbers appear exactly once, except one number, which is missing. Find this missing number.
- The XOR trick: If we have a sequence of XOR operations a ^ b ^ c ^ ..., then we can remove all pairs of duplicated values without affecting the result.
- ```
    a ^ b ^ c ^ a ^ b     # Commutativity
  = a ^ a ^ b ^ b ^ c     # Using x ^ x = 0
  = 0 ^ 0 ^ c             # Using x ^ 0 = x (and commutativity)
  = c
```
- In-Place Swapping (without intermediary variable)
- ```
  x ^= y
  y ^= x
  x ^= y
```
- Finding the Missing Number
- Finding the Duplicate Number
- You are given an array A of n + 1 integers which are in the range between 1 and n. All numbers appear exactly once, except one number, which is duplicated. Find this duplicated number.
- Finding Two Missing/Duplicate Numbers
A Neat XOR Trick
- nznrnfrfntjfmvfwmzdfjlvtqnbhcprsg Within this string, you want to find the first W-character window in which every character is unique.
- Give each letter a maskable unique integer bit

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