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  1. #include <iostream>
  2. #include <cmath>
  3. #include <vector>
  4.  
  5. using namespace std;
  6. using Blob = vector<uint8_t>;
  7.  
  8. // http://stackoverflow.com/questions/29547628/convert-uint8-t-hex-value-to-binary
  9. void toBinary(uint8_t a) {
  10. 	int tmp = 0;
  11.     for(uint8_t i=0x80;i!=0;i>>=1) {
  12.     	if ( tmp++ % 4 == 0 ) 
  13.     		cout << " ";
  14.  
  15.         cout << ((a&i)?'1':'0');
  16.     }
  17. }
  18.  
  19. void toBinary(Blob p) {
  20. 	for (size_t i = 0; i < p.size(); i++ )
  21. 		toBinary(p[i]);
  22. }
  23.  
  24. // Unexpect behavior if a prefix without padding is given.
  25. // No way to check if there is a prefix or if there is not
  26. size_t realPrefix(Blob p) {
  27. 	for ( size_t i = p.size() - 1; i >= 0; i-- ) { 
  28. 		uint8_t j = 0x01;
  29. 		for ( size_t pos = 0; pos < 8; pos++, j <<= 1 )
  30. 			if ( (p[i] & j) != 0x00 )
  31. 				return pos + ( p.size() - 1 - i) * 8;
  32. 	}
  33.  
  34. 	// Should never append
  35. 	return p.size() * 8;
  36. }
  37.  
  38. int main() {
  39.  
  40. 	Blob p; // Test Blob	
  41. 	p.push_back(0xBA); // 1011 1010
  42. 	p.push_back(0x80); // 1000 0000 -> Padding
  43. 	Blob out(2 * p.size()); // ceil(p.size_ * 2. / 8.);
  44.  
  45.     cout << "Prefix with unknown value :" ;
  46.     toBinary(p);
  47.  
  48. 	for ( size_t i = 0; i < p.size(); i++ ) {
  49.     	for ( int b = 0, shift = 0; b < 8; b++, shift += 2) {
  50. 			if ( shift >= 8 ) 
  51. 				shift = 0;
  52.  
  53. 			/* 1 -> 11 [0xC0], 0 -> 10 [0x80], shift in right place */
  54.     		uint8_t mout = (( p[i] & (0x80 >> b ) ) ? 0xC0 : 0x80) >> shift;
  55. 			out[i * 2 + (b >= 4)] |= mout; 
  56.     	}
  57. 	}
  58.  
  59. 	cout << endl << "Output : " ;
  60.     toBinary(out);
  61.     cout << endl;
  62.  
  63.     exit(0);
  64. }
  65.  
Success #stdin #stdout 0s 3416KB
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Standard input is empty
stdout
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Prefix with unknown value : 1011 1010 1000 0000
Output :  1110 1111 1110 1110 1110 1010 1010 1010
https://ideone.com/eiCZNS
language:
C++14 (gcc 8.3)
created:
7 years ago
visibility:
public

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