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  1. #include <stdio.h>
  2.  
  3. unsigned char FFMul(unsigned char a, unsigned char b) {
  4.    unsigned char aa = a, bb = b, r = 0, t;
  5.    while (aa != 0) {
  6.       if ((aa & 1) != 0)
  7.          r = r ^ bb;
  8.       t = bb & 0x80;
  9.       bb = bb << 1;
  10.       if (t != 0)
  11.          bb = bb ^ 0x1b;
  12.       aa = aa >> 1; 
  13.    }
  14.    return r;
  15. }
  16.  
  17. int main(void) {
  18. 	unsigned char x1 = 0x63;
  19. 	unsigned char x2 = FFMul(x1, 2);
  20. 	unsigned char x4 = FFMul(x2, 2);
  21. 	unsigned char x8 = FFMul(x4, 2);
  22.  
  23. 	unsigned char x7_calc = FFMul(x1, 7);
  24. 	unsigned char x7_xor1 = FFMul(x1, 5) ^ FFMul(x1, 2);
  25. 	unsigned char x7_xor2 = FFMul(x1, 8) ^ FFMul(x1, 1);
  26.  
  27. 	printf("x1 = %#4x\n", x1);
  28. 	printf("x2 = %#4x\n", x2);
  29. 	printf("x4 = %#4x\n", x4);
  30. 	printf("x8 = %#4x\n", x8);
  31. 	printf("\n");
  32.  
  33. 	printf("x7 = %#4x (calc)\n", x7_calc);
  34. 	printf("x7 = %#4x (x5 + x2)\n", x7_xor1);
  35. 	printf("x7 = %#4x (x8 - x1)\n", x7_xor2);
  36.  
  37. 	return 0;
  38. }
  39.  
Success #stdin #stdout 0s 2292KB
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stdout
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x1 = 0x63
x2 = 0xc6
x4 = 0x97
x8 = 0x35

x7 = 0x32 (calc)
x7 = 0x32 (x5 + x2)
x7 = 0x56 (x8 - x1)
https://ideone.com/tMcbLm
language:
C (gcc 8.3)
created:
11 years ago
visibility:
public

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