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  1. #include <stdio.h>
  2. #include <stdint.h>
  3.  
  4.  
  5. uint32_t crc_table[256];
  6.  
  7. /* Run this function previously */
  8. void make_crc_table(void) {
  9.     for (uint32_t i = 0; i < 256; i++) {
  10.         uint32_t c = i;
  11.         for (int j = 0; j < 8; j++) {
  12.             c = (c & 1) ? (0xEDB88320 ^ (c >> 1)) : (c >> 1);
  13.         }
  14.         crc_table[i] = c;
  15.     }
  16. }
  17.  
  18. uint32_t crc32_wikipedia(const uint8_t *buf, size_t len) {
  19.     uint32_t c = 0xFFFFFFFF;
  20.     for (size_t i = 0; i < len; i++) {
  21.         c = crc_table[(c ^ buf[i]) & 0xFF] ^ (c >> 8);
  22.     }
  23.     return c ^ 0xFFFFFFFF;
  24. }
  25.  
  26.  
  27.  
  28. const uint32_t Polynomial = 0xEDB88320;
  29.  
  30.  uint32_t crc32_bitwise(const void* data, size_t length, uint32_t previousCrc32 = 0) { 
  31.      uint32_t crc = ~previousCrc32; // same as previousCrc32 ^ 0xFFFFFFFF 
  32.      unsigned char* current = (unsigned char*) data; 
  33.      while (length--) { 
  34.          crc ^= *current++; 
  35.          for (unsigned int j = 0; j < 8; j++) 
  36.          if (crc & 1) crc = (crc >> 1) ^ Polynomial; else crc = crc >> 1; 
  37.  
  38.      } 
  39.      return ~crc; // same as crc ^ 0xFFFFFFFF 
  40. } 
  41.  
  42.  
  43. int main()
  44. {
  45.     make_crc_table();
  46.     printf("%08x\n", crc32_wikipedia((const uint8_t *)"abcdefghijklmnopqrstuvwxyz", 26));
  47.     printf("%08x\n", crc32_bitwise("abcdefghijklmnopqrstuvwxyz", 26, 0));
  48. }
Success #stdin #stdout 0s 2896KB
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4c2750bd
4c2750bd
https://ideone.com/pWLVSo
language:
C++ (gcc 8.3)
created:
11 years ago
visibility:
public

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