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  1. #include <iostream>
  2. #include <inttypes.h>
  3.  
  4. uint64_t fletcher64_A(const uint8_t * data, uint64_t count)
  5. {
  6. 	// calculate how many full double words the input has
  7. 	uint64_t dwords = count / 4;
  8. 	// now calculate the flechter-64 checksum from double words
  9. 	uint64_t sum1 = 0;
  10. 	uint64_t sum2 = 0;
  11. 	const uint32_t * data32 = reinterpret_cast<const uint32_t*>(data);
  12. 	for (uint64_t index = 0; index < dwords; ++index) 
  13. 	{
  14.     	sum1 = (sum1 + data32[index]) % UINT32_MAX;
  15.     	sum2 = (sum2 + sum1) % UINT32_MAX;
  16.     }
  17.     // calculate how many extra bytes, that do not fit into a double word, the input has
  18. 	uint64_t remainingBytes = count - dwords * 4;
  19.     if (remainingBytes > 0)
  20.     {
  21.     	// copy the excess bytes to our dummy variable. you could use memcpy here...
  22. 		uint32_t dummy = 0;
  23. 		for (uint64_t index = 0; index < remainingBytes; ++index)
  24. 		{
  25. 			reinterpret_cast<uint8_t*>(&dummy)[index] = data[dwords * 4 + index];
  26. 		}
  27. 		// now add the dummy on top
  28. 		sum1 = (sum1 + dummy) % UINT32_MAX;
  29. 		sum2 = (sum2 + sum1) % UINT32_MAX;
  30.     }
  31.     // build final checksum
  32.     return (sum2 << 32) | sum1;
  33. }
  34.  
  35. uint64_t fletcher64_B(const uint8_t * data, uint64_t count)
  36. {
  37. 	// calculate how many full double words the input has
  38. 	uint64_t dwords = count / 4;
  39. 	// now calculate the flechter-64 checksum from double words
  40. 	uint32_t sum1 = 0;
  41. 	uint32_t sum2 = 0;
  42. 	const uint32_t * data32 = reinterpret_cast<const uint32_t*>(data);
  43. 	for (uint64_t index = 0; index < dwords; ++index) 
  44. 	{
  45. 		sum1 += data32[index];
  46. 		sum2 += sum1;
  47.     }
  48.     // calculate how many extra bytes, that do not fit into a double word, the input has
  49. 	uint64_t remainingBytes = count - dwords * 4;
  50.     if (remainingBytes > 0)
  51.     {
  52.     	// copy the excess bytes to our dummy variable. you could use memcpy here...
  53. 		uint32_t dummy = 0;
  54. 		for (uint64_t index = 0; index < remainingBytes; ++index)
  55. 		{
  56. 			reinterpret_cast<uint8_t*>(&dummy)[index] = data[dwords * 4 + index];
  57. 		}
  58. 		// now add the dummy on top
  59. 		sum1 += dummy;
  60. 		sum2 += sum1;
  61.     }
  62.     // build final checksum
  63.     return ((uint64_t)sum2 << 32) | sum1;
  64. }
  65.  
  66. int main() {
  67. 	const std::string data = "abcdefghijklmnopqrstuvwxyz0123456789helloworld!";
  68. 	uint64_t ca = fletcher64_A(reinterpret_cast<const uint8_t*>(data.data()), data.size());
  69. 	uint64_t cb = fletcher64_B(reinterpret_cast<const uint8_t*>(data.data()), data.size());
  70. 	std::cout << "String size: " << data.size() << ", checksum a: 0x" << std::hex << ca << ", checksum b: 0x" << cb << std::endl;
  71. 	return 0;
  72. }
Success #stdin #stdout 0s 3472KB
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stdin
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Standard input is empty
stdout
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String size: 47, checksum a: 0x90651cd4152ab0aa, checksum b: 0x90651cb7152ab0a6
https://ideone.com/j4bCWA
language:
C++14 (gcc 8.3)
created:
8 years ago
visibility:
public

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