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  1. #include <stdio.h>
  2. #include <stdint.h>
  3.  
  4. typedef struct {
  5. 	uint8_t dst;
  6. 	uint8_t l;
  7. 	uint8_t crc_m;
  8. 	uint8_t h;
  9. 	uint8_t crc_l;
  10. } cct_frame_t;
  11.  
  12. static cct_frame_t cct_frame;
  13.  
  14.  
  15.  
  16. uint16_t calculate_crc_loop_CCITT_A( int l, uint8_t *p, uint16_t seed )
  17. {
  18.     int i, j;
  19.     uint16_t crc = seed;
  20.     for ( i = 0; i < l; ++i )
  21.     {
  22.         crc ^= ( p[ i ] << 8 );
  23.         for ( j = 0; j < 8; ++j )
  24.         {
  25.             if ( crc & 0x8000 ){
  26.                 crc = ( crc << 1 ) ^ 0x1021; // 0001.0000 0010.0001 = x^12 + x^5 + 1 ( + x^16 )
  27.             }
  28.             else{
  29.                 crc <<= 1;
  30.             }
  31.         }
  32.     }
  33.     return crc;
  34. }
  35.  
  36. int main(void) {
  37. 	uint16_t crc = 0;
  38.  
  39. 	cct_frame.dst = 0;
  40. 	cct_frame.l = 0;
  41. 	cct_frame.h = 4;
  42. 	crc = calculate_crc_loop_CCITT_A(1, &cct_frame.dst, crc);
  43. 	crc = calculate_crc_loop_CCITT_A(1, &cct_frame.l, crc);
  44. 	crc = calculate_crc_loop_CCITT_A(1, &cct_frame.h, crc);
  45. 	cct_frame.crc_m = 0xFF & (crc >> 8);
  46. 	cct_frame.crc_l = 0xFF & crc;
  47.  
  48. 	printf ("%x %x %x %x %x\n %x", cct_frame.dst, cct_frame.l, cct_frame.crc_m, cct_frame.h, cct_frame.crc_l, crc);
  49.  
  50. 	// your code goes here
  51. 	return 0;
  52. }
  53.  
Success #stdin #stdout 0s 5504KB
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0 0 40 4 84
 4084
https://ideone.com/e0l7qz
language:
C (gcc 8.3)
created:
2 years ago
visibility:
public

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