402 lines
11 KiB
Plaintext
402 lines
11 KiB
Plaintext
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subroutine bpdecode174(llr,apmask,maxiterations,decoded,cw,nharderror,iter)
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!
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! A log-domain belief propagation decoder for the (174,87) code.
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!
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integer, parameter:: N=174, K=87, M=N-K
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integer*1 codeword(N),cw(N),apmask(N)
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integer colorder(N)
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integer*1 decoded(K)
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integer Nm(7,M) ! 5, 6, or 7 bits per check
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integer Mn(3,N) ! 3 checks per bit
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integer synd(M)
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real tov(3,N)
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real toc(7,M)
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real tanhtoc(7,M)
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real zn(N)
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real llr(N)
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real Tmn
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integer nrw(M)
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data colorder/ &
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0, 1, 2, 3, 30, 4, 5, 6, 7, 8, 9, 10, 11, 32, 12, 40, 13, 14, 15, 16,&
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17, 18, 37, 45, 29, 19, 20, 21, 41, 22, 42, 31, 33, 34, 44, 35, 47, 51, 50, 43,&
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36, 52, 63, 46, 25, 55, 27, 24, 23, 53, 39, 49, 59, 38, 48, 61, 60, 57, 28, 62,&
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56, 58, 65, 66, 26, 70, 64, 69, 68, 67, 74, 71, 54, 76, 72, 75, 78, 77, 80, 79,&
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73, 83, 84, 81, 82, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99,&
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100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,&
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120,121,122,123,124,125,126,127,128,129,130,131,132,133,134,135,136,137,138,139,&
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140,141,142,143,144,145,146,147,148,149,150,151,152,153,154,155,156,157,158,159,&
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160,161,162,163,164,165,166,167,168,169,170,171,172,173/
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data Mn/ &
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1, 25, 69, &
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2, 5, 73, &
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3, 32, 68, &
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4, 51, 61, &
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6, 63, 70, &
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7, 33, 79, &
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8, 50, 86, &
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9, 37, 43, &
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10, 41, 65, &
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11, 14, 64, &
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12, 75, 77, &
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13, 23, 81, &
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15, 16, 82, &
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17, 56, 66, &
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18, 53, 60, &
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19, 31, 52, &
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20, 67, 84, &
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21, 29, 72, &
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22, 24, 44, &
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26, 35, 76, &
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27, 36, 38, &
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28, 40, 42, &
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30, 54, 55, &
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34, 49, 87, &
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39, 57, 58, &
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45, 74, 83, &
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46, 62, 80, &
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47, 48, 85, &
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59, 71, 78, &
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1, 50, 53, &
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2, 47, 84, &
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3, 25, 79, &
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4, 6, 14, &
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5, 7, 80, &
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8, 34, 55, &
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9, 36, 69, &
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10, 43, 83, &
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11, 23, 74, &
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12, 17, 44, &
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13, 57, 76, &
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15, 27, 56, &
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16, 28, 29, &
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18, 19, 59, &
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20, 40, 63, &
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21, 35, 52, &
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22, 54, 64, &
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24, 62, 78, &
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26, 32, 77, &
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30, 72, 85, &
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31, 65, 87, &
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33, 39, 51, &
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37, 48, 75, &
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38, 70, 71, &
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41, 42, 68, &
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45, 67, 86, &
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46, 81, 82, &
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49, 66, 73, &
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58, 60, 66, &
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61, 65, 85, &
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1, 14, 21, &
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2, 13, 59, &
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3, 67, 82, &
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4, 32, 73, &
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5, 36, 54, &
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6, 43, 46, &
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7, 28, 75, &
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8, 33, 71, &
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9, 49, 76, &
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10, 58, 64, &
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11, 48, 68, &
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12, 19, 45, &
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15, 50, 61, &
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16, 22, 26, &
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17, 72, 80, &
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18, 40, 55, &
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20, 35, 51, &
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23, 25, 34, &
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24, 63, 87, &
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27, 39, 74, &
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29, 78, 83, &
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30, 70, 77, &
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31, 69, 84, &
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22, 37, 86, &
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38, 41, 81, &
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42, 44, 57, &
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47, 53, 62, &
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52, 56, 79, &
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60, 75, 81, &
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1, 39, 77, &
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2, 16, 41, &
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3, 31, 54, &
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4, 36, 78, &
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5, 45, 65, &
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6, 57, 85, &
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7, 14, 49, &
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8, 21, 46, &
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9, 15, 72, &
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10, 20, 62, &
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11, 17, 71, &
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12, 34, 47, &
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13, 68, 86, &
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18, 23, 43, &
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19, 64, 73, &
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24, 48, 79, &
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25, 70, 83, &
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26, 80, 87, &
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27, 32, 40, &
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28, 56, 69, &
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29, 63, 66, &
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30, 42, 50, &
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33, 37, 82, &
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35, 60, 74, &
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38, 55, 84, &
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44, 52, 61, &
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51, 53, 72, &
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58, 59, 67, &
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47, 56, 76, &
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1, 19, 37, &
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2, 61, 75, &
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3, 8, 66, &
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4, 60, 84, &
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5, 34, 39, &
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6, 26, 53, &
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7, 32, 57, &
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9, 52, 67, &
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10, 12, 15, &
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11, 51, 69, &
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13, 14, 65, &
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16, 31, 43, &
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17, 20, 36, &
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18, 80, 86, &
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21, 48, 59, &
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22, 40, 46, &
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23, 33, 62, &
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24, 30, 74, &
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25, 42, 64, &
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27, 49, 85, &
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28, 38, 73, &
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29, 44, 81, &
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35, 68, 70, &
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41, 63, 76, &
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45, 49, 71, &
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50, 58, 87, &
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48, 54, 83, &
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13, 55, 79, &
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77, 78, 82, &
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1, 2, 24, &
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3, 6, 75, &
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4, 56, 87, &
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5, 44, 53, &
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7, 50, 83, &
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8, 10, 28, &
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9, 55, 62, &
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11, 29, 67, &
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12, 33, 40, &
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14, 16, 20, &
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15, 35, 73, &
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17, 31, 39, &
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18, 36, 57, &
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19, 46, 76, &
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21, 42, 84, &
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22, 34, 59, &
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23, 26, 61, &
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25, 60, 65, &
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27, 64, 80, &
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30, 37, 66, &
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32, 45, 72, &
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38, 51, 86, &
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41, 77, 79, &
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43, 56, 68, &
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47, 74, 82, &
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40, 52, 78, &
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54, 61, 71, &
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46, 58, 69/
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data Nm/ &
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1, 30, 60, 89, 118, 147, 0, &
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2, 31, 61, 90, 119, 147, 0, &
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3, 32, 62, 91, 120, 148, 0, &
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4, 33, 63, 92, 121, 149, 0, &
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2, 34, 64, 93, 122, 150, 0, &
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5, 33, 65, 94, 123, 148, 0, &
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6, 34, 66, 95, 124, 151, 0, &
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7, 35, 67, 96, 120, 152, 0, &
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8, 36, 68, 97, 125, 153, 0, &
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9, 37, 69, 98, 126, 152, 0, &
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10, 38, 70, 99, 127, 154, 0, &
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11, 39, 71, 100, 126, 155, 0, &
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12, 40, 61, 101, 128, 145, 0, &
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10, 33, 60, 95, 128, 156, 0, &
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13, 41, 72, 97, 126, 157, 0, &
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13, 42, 73, 90, 129, 156, 0, &
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14, 39, 74, 99, 130, 158, 0, &
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15, 43, 75, 102, 131, 159, 0, &
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16, 43, 71, 103, 118, 160, 0, &
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17, 44, 76, 98, 130, 156, 0, &
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18, 45, 60, 96, 132, 161, 0, &
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19, 46, 73, 83, 133, 162, 0, &
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12, 38, 77, 102, 134, 163, 0, &
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19, 47, 78, 104, 135, 147, 0, &
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1, 32, 77, 105, 136, 164, 0, &
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20, 48, 73, 106, 123, 163, 0, &
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21, 41, 79, 107, 137, 165, 0, &
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22, 42, 66, 108, 138, 152, 0, &
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18, 42, 80, 109, 139, 154, 0, &
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23, 49, 81, 110, 135, 166, 0, &
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16, 50, 82, 91, 129, 158, 0, &
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3, 48, 63, 107, 124, 167, 0, &
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6, 51, 67, 111, 134, 155, 0, &
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24, 35, 77, 100, 122, 162, 0, &
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20, 45, 76, 112, 140, 157, 0, &
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21, 36, 64, 92, 130, 159, 0, &
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8, 52, 83, 111, 118, 166, 0, &
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21, 53, 84, 113, 138, 168, 0, &
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25, 51, 79, 89, 122, 158, 0, &
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22, 44, 75, 107, 133, 155, 172, &
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9, 54, 84, 90, 141, 169, 0, &
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22, 54, 85, 110, 136, 161, 0, &
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8, 37, 65, 102, 129, 170, 0, &
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19, 39, 85, 114, 139, 150, 0, &
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26, 55, 71, 93, 142, 167, 0, &
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27, 56, 65, 96, 133, 160, 174, &
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28, 31, 86, 100, 117, 171, 0, &
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28, 52, 70, 104, 132, 144, 0, &
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24, 57, 68, 95, 137, 142, 0, &
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7, 30, 72, 110, 143, 151, 0, &
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4, 51, 76, 115, 127, 168, 0, &
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16, 45, 87, 114, 125, 172, 0, &
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15, 30, 86, 115, 123, 150, 0, &
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23, 46, 64, 91, 144, 173, 0, &
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23, 35, 75, 113, 145, 153, 0, &
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14, 41, 87, 108, 117, 149, 170, &
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25, 40, 85, 94, 124, 159, 0, &
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25, 58, 69, 116, 143, 174, 0, &
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29, 43, 61, 116, 132, 162, 0, &
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15, 58, 88, 112, 121, 164, 0, &
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4, 59, 72, 114, 119, 163, 173, &
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27, 47, 86, 98, 134, 153, 0, &
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5, 44, 78, 109, 141, 0, 0, &
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10, 46, 69, 103, 136, 165, 0, &
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9, 50, 59, 93, 128, 164, 0, &
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14, 57, 58, 109, 120, 166, 0, &
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17, 55, 62, 116, 125, 154, 0, &
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3, 54, 70, 101, 140, 170, 0, &
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1, 36, 82, 108, 127, 174, 0, &
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5, 53, 81, 105, 140, 0, 0, &
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29, 53, 67, 99, 142, 173, 0, &
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18, 49, 74, 97, 115, 167, 0, &
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2, 57, 63, 103, 138, 157, 0, &
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26, 38, 79, 112, 135, 171, 0, &
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11, 52, 66, 88, 119, 148, 0, &
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20, 40, 68, 117, 141, 160, 0, &
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11, 48, 81, 89, 146, 169, 0, &
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29, 47, 80, 92, 146, 172, 0, &
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6, 32, 87, 104, 145, 169, 0, &
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27, 34, 74, 106, 131, 165, 0, &
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12, 56, 84, 88, 139, 0, 0, &
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13, 56, 62, 111, 146, 171, 0, &
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26, 37, 80, 105, 144, 151, 0, &
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17, 31, 82, 113, 121, 161, 0, &
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28, 49, 59, 94, 137, 0, 0, &
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7, 55, 83, 101, 131, 168, 0, &
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24, 50, 78, 106, 143, 149, 0/
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data nrw/ &
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6,6,6,6,6,6,6,6,6,6, &
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6,6,6,6,6,6,6,6,6,6, &
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6,6,6,6,6,6,6,6,6,6, &
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6,6,6,6,6,6,6,6,6,7, &
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6,6,6,6,6,7,6,6,6,6, &
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6,6,6,6,6,7,6,6,6,6, &
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7,6,5,6,6,6,6,6,6,5, &
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6,6,6,6,6,6,6,6,6,6, &
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5,6,6,6,5,6,6/
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ncw=3
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decoded=0
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toc=0
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tov=0
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tanhtoc=0
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! initialize messages to checks
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do j=1,M
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do i=1,nrw(j)
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toc(i,j)=llr((Nm(i,j)))
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enddo
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enddo
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ncnt=0
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do iter=0,maxiterations
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! Update bit log likelihood ratios (tov=0 in iteration 0).
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do i=1,N
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if( apmask(i) .ne. 1 ) then
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zn(i)=llr(i)+sum(tov(1:ncw,i))
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else
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zn(i)=llr(i)
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endif
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enddo
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! Check to see if we have a codeword (check before we do any iteration).
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cw=0
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where( zn .gt. 0. ) cw=1
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ncheck=0
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do i=1,M
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synd(i)=sum(cw(Nm(1:nrw(i),i)))
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||
|
|
if( mod(synd(i),2) .ne. 0 ) ncheck=ncheck+1
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||
|
|
! if( mod(synd(i),2) .ne. 0 ) write(*,*) 'check ',i,' unsatisfied'
|
||
|
|
enddo
|
||
|
|
! write(*,*) 'number of unsatisfied parity checks ',ncheck
|
||
|
|
if( ncheck .eq. 0 ) then ! we have a codeword - reorder the columns and return it
|
||
|
|
codeword=cw(colorder+1)
|
||
|
|
decoded=codeword(M+1:N)
|
||
|
|
nerr=0
|
||
|
|
do i=1,N
|
||
|
|
if( (2*cw(i)-1)*llr(i) .lt. 0.0 ) nerr=nerr+1
|
||
|
|
enddo
|
||
|
|
nharderror=nerr
|
||
|
|
return
|
||
|
|
endif
|
||
|
|
|
||
|
|
if( iter.gt.0 ) then ! this code block implements an early stopping criterion
|
||
|
|
! if( iter.gt.10000 ) then ! this code block implements an early stopping criterion
|
||
|
|
nd=ncheck-nclast
|
||
|
|
if( nd .lt. 0 ) then ! # of unsatisfied parity checks decreased
|
||
|
|
ncnt=0 ! reset counter
|
||
|
|
else
|
||
|
|
ncnt=ncnt+1
|
||
|
|
endif
|
||
|
|
! write(*,*) iter,ncheck,nd,ncnt
|
||
|
|
if( ncnt .ge. 5 .and. iter .ge. 10 .and. ncheck .gt. 15) then
|
||
|
|
nharderror=-1
|
||
|
|
return
|
||
|
|
endif
|
||
|
|
endif
|
||
|
|
nclast=ncheck
|
||
|
|
|
||
|
|
! Send messages from bits to check nodes
|
||
|
|
do j=1,M
|
||
|
|
do i=1,nrw(j)
|
||
|
|
ibj=Nm(i,j)
|
||
|
|
toc(i,j)=zn(ibj)
|
||
|
|
do kk=1,ncw ! subtract off what the bit had received from the check
|
||
|
|
if( Mn(kk,ibj) .eq. j ) then
|
||
|
|
toc(i,j)=toc(i,j)-tov(kk,ibj)
|
||
|
|
endif
|
||
|
|
enddo
|
||
|
|
enddo
|
||
|
|
enddo
|
||
|
|
|
||
|
|
! send messages from check nodes to variable nodes
|
||
|
|
do i=1,M
|
||
|
|
tanhtoc(1:7,i)=tanh(-toc(1:7,i)/2)
|
||
|
|
enddo
|
||
|
|
|
||
|
|
do j=1,N
|
||
|
|
do i=1,ncw
|
||
|
|
ichk=Mn(i,j) ! Mn(:,j) are the checks that include bit j
|
||
|
|
Tmn=product(tanhtoc(1:nrw(ichk),ichk),mask=Nm(1:nrw(ichk),ichk).ne.j)
|
||
|
|
call platanh(-Tmn,y)
|
||
|
|
! y=atanh(-Tmn)
|
||
|
|
tov(i,j)=2*y
|
||
|
|
enddo
|
||
|
|
enddo
|
||
|
|
|
||
|
|
enddo
|
||
|
|
nharderror=-1
|
||
|
|
return
|
||
|
|
end subroutine bpdecode174
|