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  1. #include <iostream>
  2. #include <sstream>
  3. #include <vector>
  4. #include <algorithm>
  5. #include <iterator>
  6. #include <cstdint>
  7.  
  8. using namespace std;
  9.  
  10. struct TagHeader {
  11.     uint16_t tag_code;
  12.     uint32_t tag_length;
  13. };
  14.  
  15. static const int bits_per_byte = 8;
  16.  
  17. template<class int_type, class iterator_type>
  18. static int_type parse_int_le(iterator_type& i, iterator_type eof = iterator_type {}) {
  19.     std::array<unsigned char, sizeof(int_type)> bytes;
  20.     std::copy_n(i, sizeof(bytes), std::begin(bytes));
  21.     i++;
  22.     int_type value = 0;
  23.     for(int byte_offset = sizeof(int_type) - 1; byte_offset >= 0; byte_offset--) {
  24.         value |= static_cast<int_type>(bytes[byte_offset]) << byte_offset * bits_per_byte;
  25.     }
  26.     return value;
  27. }
  28.  
  29. template<class iterator_type>
  30. static TagHeader parse_tag_header(iterator_type& i, iterator_type eof) {
  31.     TagHeader h;
  32.     auto code_and_length = parse_int_le<uint16_t>(i, eof);
  33.     std::cout << "code_and_length = " << code_and_length << "\n";
  34.     h.tag_code = (code_and_length & (0xffff << 6)) >> 6; // top 10 bits are tag type
  35.     h.tag_length = code_and_length & (0xffff >> 10); // lower 6 bits are length
  36.     if(h.tag_length >= 63) {
  37.         h.tag_length = parse_int_le<uint32_t>(i, eof);
  38.     }
  39.     return h;
  40. }
  41. int main() {
  42. 	{
  43. 		stringstream sstr;
  44. 		sstr << "\x8b\x15";
  45. 		istreambuf_iterator<char> i(sstr);
  46. 		istreambuf_iterator<char> eof;
  47.  
  48. 		auto th = parse_tag_header(i, eof);
  49. 		std::cout << th.tag_length << "\n";
  50. 	}
  51. 	std::cout << "\n";
  52. 	{
  53. 		stringstream sstr;
  54. 		sstr << "\x8b\x15";
  55. 		istreambuf_iterator<char> i(sstr);
  56. 		istreambuf_iterator<char> eof;
  57.  
  58. 		std::vector<char> tag_data(2);
  59. 		std::copy_n(i, 2, tag_data.begin());
  60. 		i++;
  61.  
  62. 		auto tag_i = tag_data.begin();
  63. 		auto tag_eof = tag_data.end();
  64.  
  65. 		auto th = parse_tag_header(tag_i, tag_eof);
  66. 		std::cout << th.tag_length << "\n";
  67. 	}
  68. 	return 0;
  69. }
Success #stdin #stdout 0s 3472KB
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code_and_length = 5515
11

code_and_length = 5515
11
https://ideone.com/glkD3b
language:
C++14 (gcc 8.3)
created:
12 years ago
visibility:
public

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