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  1. #include <stdio.h>
  2. #include <math.h>
  3.  
  4. void parityCheck(char* codeWord) {
  5.   int parity[4] = {0}, i = 0, diffParity[4] = {0}, twoPower = 0, bitSum = 0;
  6.  
  7.   // Stores # of 1's for each parity bit in array.
  8.   parity[0] = (codeWord[2] - 48) + (codeWord[4] - 48) + (codeWord[6] - 48) + (codeWord[8] - 48) + (codeWord[10] - 48);
  9.   parity[1] = (codeWord[2] - 48) + (codeWord[5] - 48) + (codeWord[6] - 48) + (codeWord[9] - 48) + (codeWord[10] - 48);
  10.   parity[2] = (codeWord[4] - 48) + (codeWord[5] - 48) + (codeWord[6] - 48);
  11.   parity[3] = (codeWord[8] - 48) + (codeWord[9] - 48) + (codeWord[10] - 48);
  12.  
  13.   // Determines if sum of bits is even or odd, then tests for difference
  14.   // from actual parity bit.
  15.   for (i = 0; i < 4; i++) {
  16.     twoPower = (int)pow((double)2, i);
  17.  
  18.     if (parity[i] % 2 == 0)
  19.       parity[i] = 0;
  20.     else
  21.       parity[i] = 1;
  22.  
  23.     if ((codeWord[twoPower-1] - 48) != parity[i])
  24.       diffParity[i] = 1;
  25.   }
  26.  
  27.   // Calculates the location of the error bit.
  28.   for (i = 0; i < 4; i++) {
  29.     twoPower = (int)pow((double)2, i);
  30.     bitSum += diffParity[i]*twoPower;
  31.   }
  32.  
  33.   // Inverts bit at location of error.
  34.   if (bitSum <= 11 && bitSum > 0) {
  35.     if ((codeWord[bitSum-1] - 48)) 
  36.       codeWord[bitSum-1] = '0';
  37.     else
  38.       codeWord[bitSum-1] = '1';
  39.   }
  40. }
  41.  
  42. int pc(int codeWord) {
  43.   int parity = 0, codeWordBit, bitPos;
  44.   for (bitPos = 1; bitPos <= 11; ++bitPos) {
  45.     codeWordBit = ((codeWord >> (bitPos - 1)) & 1);
  46.     parity ^= bitPos*codeWordBit;
  47.   }
  48.   if (parity != 0)
  49.     codeWord ^= 1 << (parity - 1);
  50.   return codeWord;
  51. }
  52.  
  53. int main() {
  54.   int c, f, b, errors = 0;
  55.   char ew[12], cw[12], fw[12];
  56.   ew[11] = cw[11] = fw[11] = '\0';
  57.   for (c = 0; c != 1<<11; ++c) {
  58.     f = pc(c);
  59.     for (b = 0; b != 11; ++b) {
  60.       ew[b] = cw[b] = '0' + ((c >> b)&1);
  61.       fw[b] = '0' + ((f >> b)&1);
  62.     }
  63.     parityCheck(cw);
  64.     for (b = 0; b != 11; ++b) {
  65.       if (cw[b] != fw[b]) {
  66.         printf("%.11s: expected %.11s got %.11s\n", ew, fw, cw);
  67.         errors = 1;
  68.         break;
  69.       }
  70.     }
  71.   }
  72.   if (errors == 0)
  73.     printf("No erros :-)\n");
  74.   return errors;
  75. }
  76.  
Success #stdin #stdout 0s 3340KB
comments (?)
stdin
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Standard input is empty
stdout
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No erros :-)
https://ideone.com/jhZWcr
language:
C++ (gcc 8.3)
created:
10 years ago
visibility:
public

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