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  1. #include <stdio.h>
  2. #include <stdint.h>
  3.  
  4. void decode_bch_bin(uint16_t enc, uint16_t* dec);
  5. void decodebch_bi1(int *bits, int *decbits);
  6. uint32_t getbitu(uint8_t* buff, uint32_t pos, uint32_t len);
  7. void bits2byte(int *bits, int nbits, int nbin, int right, uint8_t *bin);
  8.  
  9. union bch_reg{
  10.     uint8_t val;
  11.     struct {
  12.         uint8_t b0:1;
  13.         uint8_t b1:1;
  14.         uint8_t b2:1;
  15.         uint8_t b3:1;
  16.     } bits;
  17. };
  18.  
  19. int main(void) {
  20. 	int32_t bits[15] = {1,-1,1,-1,1,-1,1,-1,1,-1,1,-1,1,-1,1};
  21. 	int32_t bits_res[15];
  22. 	uint16_t dec = 0, bin = 0x5555;
  23. 	decodebch_bi1(bits, bits_res);
  24. 	decode_bch_bin(bin , &dec);
  25. 	{
  26. 		int i = 0;
  27. 		for(i = 0; i < 15; i++) {
  28. 			printf(" %d",bits_res[i]);
  29. 		}
  30. 	}
  31. 	printf("\n%x",dec);
  32. 	return 0;
  33. }
  34.  
  35. void decode_bch_bin(uint16_t enc, uint16_t* dec)
  36. {
  37.     union bch_reg reg;
  38.     uint8_t i, bit;
  39.     uint16_t err[15] = {0, 1, 2, 16, 4, 256, 32, 1024, 8, 16384, 512, 128, 
  40.                         64, 8192, 2048, 4096}; 
  41.     /* see Table 5.2 */
  42.     uint8_t ind = 0;
  43.  
  44.     /* BCH decoding (Fig 5-4) */
  45.     for (i = 0; i < 15; i++) {
  46.         bit = reg.bits.b3;
  47.         reg.bits.b3 = reg.bits.b2;
  48.         reg.bits.b2 = reg.bits.b1;
  49.         reg.bits.b1 = reg.bits.b0;
  50.         reg.bits.b0 = (enc & (1 << i))^bit;
  51.         reg.bits.b1 ^= bit;
  52.     }
  53.     printf("reg val = %u\n", reg.val);
  54.     /*error correction*/
  55.     enc ^= err[reg.val];
  56.  
  57.     *dec = enc;
  58. }
  59.  
  60.  
  61. void decodebch_bi1(int *bits, int *decbits)
  62. {
  63.     int i,bit,err,reg[4]={1,1,1,1};
  64.     int errind[15]={14,13,10,12,6,9,4,11,0,5,7,8,1,3,2}; /* see Table 5.2 */
  65.     uint8_t bin;
  66.  
  67.     /* copy input to output */
  68.     for (i=0;i<15;i++) decbits[i]=bits[i];
  69.  
  70.     /* BCH decoding (Fig 5-4) */
  71.     for (i=0;i<15;i++) {
  72.         bit=reg[3];
  73.         reg[3]=reg[2]; reg[2]=reg[1]; reg[1]=reg[0];
  74.         reg[0]=bits[i]*bit;
  75.         reg[1]*=bit;
  76.     }
  77.     /* get error index */
  78.     bits2byte(reg,4,1,0,&bin);
  79.     printf("bin = %u\n", getbitu(&bin,0,4));
  80.     err=errind[getbitu(&bin,0,4)]; /* error index */
  81.  
  82.     /* error correction */
  83.     if (err>0) decbits[err-1]*=-1;
  84. }
  85.  
  86. void bits2byte(int *bits, int nbits, int nbin, int right, uint8_t *bin)
  87. {
  88.     int i,j,rem,bitscpy[8192]={0};
  89.     unsigned char b;
  90.     rem=8*nbin-nbits;
  91.  
  92.     memcpy(&bitscpy[right?rem:0],bits,sizeof(int)*nbits);
  93.  
  94.     for (i=0;i<nbin;i++) {
  95.         b=0;
  96.         for (j=0;j<8;j++) {
  97.             b<<=1;
  98.             if (bitscpy[i*8+j]<0) b|=0x01; /* -1=>1, 1=>0 */
  99.         }
  100.         bin[i]=b;
  101.     }
  102. }
  103.  
  104. uint32_t getbitu(uint8_t* buff, uint32_t pos, uint32_t len)
  105. {
  106.     uint32_t i, bits=0;
  107.     for (i = pos; i < pos + len; i++) {
  108.         bits = (bits << 1) + ((buff[i/8] >> (7 - i%8)) & 1u);
  109.     }
  110.     return bits;
  111. }
Success #stdin #stdout 0s 5304KB
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stdin
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Standard input is empty
stdout
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bin = 7
reg val = 9
 1 -1 1 -1 1 -1 1 -1 1 -1 -1 -1 1 -1 1
1555
https://ideone.com/Qj2SWm
language:
C (gcc 8.3)
created:
13 days ago
visibility:
public

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