Xor Party Tricks

The article presents four code examples demonstrating the use of the XOR bitwise operator in programming. The examples include finding a missing number in a sequence, encrypting text with a key, traversing a linked list using XOR-linked pointers, and swapping two integer values without a temporary variable.

dup.c This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters. Learn more about bidirectional Unicode characters Show hidden characters include <stdio.h include <stdlib.h include <time.h int xs = {7,62,2,46,73,43,26,82,5,95,57,56,44,21,40,79,13,6,9,8,72,59,65,81,60,78,13,85,87,58,48,25,32,47,67,4,31,19,33,1,92,14,53,89,84,54,29,10,17,3,77,70,45,97,34,23,86,55,15,64,68,83,76,41,18,39,94,22,74,11,69,49,12,35,20,90,100,98,36,63,91,38,66,93,50,96,61,71,75,37,52,88,30,28,99,27,42,51,80,24,16}; int main { int x = 0; for int i = 1; i <= 100; ++i { x ^= i; } size t n = sizeof xs /sizeof xs 0 ; for int i = 0; i < n; ++i { x ^= xs i ; } printf "%d\n", x ; return 0; } encrypt.py This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters. Learn more about bidirectional Unicode characters Show hidden characters def encrypt m , k : return '' . join chr ord a ^ k for a in m ll.c This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters. Learn more about bidirectional Unicode characters Show hidden characters include <assert.h include <stdio.h include <stdlib.h include <stdint.h include <string.h typedef struct { int value; uintptr t xored; } Node; Node node create int value { Node node = malloc sizeof node ; memset node, 0, sizeof node ; node- value = value; return node; } typedef struct { Node begin; Node end; } Linked List; void ll append Linked List ll, int value { if ll- end == NULL { assert ll- begin == NULL ; ll- end = node create value ; ll- begin = ll- end; } else { Node node = node create value ; node- xored = uintptr t ll- end; ll- end- xored ^= uintptr t node; ll- end = node; } } Node node next Node node, uintptr t prev { Node next = Node node- xored^ prev ; prev = uintptr t node; return next; } int main { Linked List xs = {0}; for int x = 5; x <= 10; ++x { ll append &xs, x ; } uintptr t prev = 0; for Node iter = xs.end; iter; iter = node next iter, &prev { printf "%d\n", iter- value ; } return 0; } swap.c This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters. Learn more about bidirectional Unicode characters Show hidden characters include <stdio.h int main { int a = 69 ; int b = 420 ; printf "%d %d\n" , a , b ; a ^= b ; // a = 69^420, b = 420 b ^= a ; // a = 69^420, b = 69 a ^= b ; // a = 420, b = 69 printf "%d %d\n" , a , b ; return 0 ; }