483 lines
12 KiB
Fortran
483 lines
12 KiB
Fortran
subroutine bpdecode204(llr,apmask,maxiterations,decoded,cw,nharderror,iter)
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!
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! A log-domain belief propagation decoder for the (204,68) code.
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!
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integer, parameter:: N=204, K=68, 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(6,M) ! 4, 5, or 6 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(6,M)
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real tanhtoc(6,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, 4, 5, 47, 6, 7, 8, 9, 10, 11, 12, 58, 55, 13, &
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14, 15, 46, 17, 18, 60, 19, 20, 21, 22, 23, 24, 25, 57, 26, 27, 49, &
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28, 52, 65, 16, 50, 73, 59, 68, 63, 29, 30, 31, 32, 51, 62, 56, 66, &
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45, 33, 34, 53, 67, 35, 36, 37, 61, 69, 54, 38, 71, 82, 39, 77, 80, &
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83, 78, 84, 48, 41, 85, 40, 64, 75, 96, 74, 72, 76, 86, 87, 89, 90, &
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79, 70, 92, 99, 93,101, 95,100, 97, 94, 42, 98,103,105,102, 43,104, &
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88, 44,106, 81,107,110,108,111,112,109,113,114,117,118,116,121,115, &
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119,122,120,125,129,124,127,126,128, 91,123,133,131,130,134,135,137, &
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136,132,138,139,140,141,142,143,144,145,146,147,148,149,150,151,152, &
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153,154,155,156,157,158,159,160,161,162,163,164,165,166,167,168,169, &
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170,171,172,173,174,175,176,177,178,179,180,181,182,183,184,185,186, &
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187,188,189,190,191,192,193,194,195,196,197,198,199,200,201,202,203/
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data Mn/ &
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1, 38, 107, &
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2, 7, 114, &
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3, 48, 106, &
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4, 79, 94, &
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5, 97, 108, &
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6, 50, 122, &
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8, 78, 134, &
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9, 55, 65, &
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10, 62, 100, &
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11, 16, 99, &
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12, 113, 119, &
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13, 31, 125, &
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14, 15, 127, &
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17, 87, 103, &
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18, 81, 98, &
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19, 43, 77, &
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20, 102, 130, &
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21, 36, 111, &
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22, 23, 60, &
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24, 39, 112, &
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25, 37, 42, &
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26, 41, 51, &
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27, 67, 70, &
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28, 64, 136, &
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29, 61, 68, &
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30, 91, 124, &
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32, 80, 121, &
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33, 40, 117, &
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34, 35, 90, &
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44, 88, 93, &
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45, 128, 133, &
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46, 56, 69, &
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47, 49, 52, &
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53, 76, 131, &
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54, 104, 116, &
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57, 84, 86, &
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58, 120, 135, &
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59, 75, 92, &
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63, 71, 109, &
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66, 74, 126, &
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72, 85, 105, &
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73, 82, 95, &
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83, 89, 123, &
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96, 115, 118, &
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101, 110, 129, &
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52, 99, 132, &
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1, 3, 20, &
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2, 77, 89, &
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4, 72, 75, &
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5, 34, 79, &
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6, 24, 130, &
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7, 48, 88, &
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8, 36, 116, &
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9, 71, 114, &
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10, 87, 101, &
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11, 22, 121, &
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12, 50, 64, &
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13, 39, 53, &
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14, 41, 78, &
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15, 68, 96, &
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16, 83, 90, &
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17, 23, 45, &
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18, 47, 126, &
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19, 70, 91, &
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21, 57, 76, &
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25, 110, 117, &
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26, 82, 135, &
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27, 46, 58, &
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28, 37, 56, &
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29, 66, 102, &
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30, 62, 125, &
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31, 85, 93, &
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32, 104, 113, &
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33, 81, 92, &
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35, 100, 118, &
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38, 95, 133, &
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40, 86, 109, &
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42, 61, 124, &
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43, 59, 119, &
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44, 49, 134, &
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51, 97, 122, &
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54, 105, 107, &
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55, 128, 136, &
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60, 67, 84, &
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63, 112, 115, &
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65, 74, 131, &
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69, 80, 94, &
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73, 98, 123, &
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103, 130, 134, &
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46, 106, 111, &
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1, 84, 108, &
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120, 129, 132, &
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65, 75, 127, &
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2, 80, 101, &
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3, 118, 119, &
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4, 52, 124, &
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5, 13, 68, &
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6, 27, 81, &
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7, 51, 76, &
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8, 77, 108, &
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9, 31, 58, &
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10, 18, 57, &
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11, 63, 105, &
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12, 14, 132, &
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15, 56, 123, &
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16, 21, 128, &
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17, 37, 59, &
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19, 85, 126, &
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20, 71, 91, &
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22, 26, 117, &
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23, 79, 98, &
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24, 32, 95, &
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25, 90, 93, &
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28, 49, 109, &
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29, 116, 120, &
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30, 54, 136, &
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33, 53, 107, &
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34, 64, 103, &
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35, 39, 67, &
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36, 71, 73, &
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38, 47, 125, &
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40, 66, 94, &
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41, 70, 104, &
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42, 55, 112, &
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43, 44, 82, &
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29, 45, 88, &
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48, 86, 127, &
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50, 72, 135, &
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60, 74, 96, &
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61, 121, 131, &
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62, 78, 92, &
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69, 100, 133, &
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83, 122, 129, &
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87, 97, 106, &
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89, 102, 113, &
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24, 99, 108, &
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20, 72, 110, &
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111, 115, 117, &
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35, 52, 114, &
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1, 44, 94, &
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2, 23, 107, &
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3, 81, 136, &
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4, 8, 96, &
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5, 37, 70, &
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6, 43, 131, &
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7, 103, 115, &
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9, 94, 122, &
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10, 68, 82, &
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11, 56, 88, &
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12, 46, 126, &
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13, 16, 75, &
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14, 79, 112, &
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15, 47, 110, &
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17, 36, 39, &
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18, 63, 120, &
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19, 22, 55, &
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21, 49, 113, &
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25, 54, 57, &
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26, 89, 125, &
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27, 101, 109, &
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28, 31, 60, &
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30, 74, 97, &
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32, 92, 93, &
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33, 83, 91, &
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34, 58, 121, &
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38, 65, 111, &
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40, 99, 118, &
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3, 41, 61, &
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42, 50, 100, &
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45, 78, 106, &
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48, 95, 129, &
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51, 85, 133, &
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53, 59, 69, &
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11, 62, 66, &
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64, 73, 124, &
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67, 123, 134, &
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76, 104, 132, &
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77, 100, 127, &
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36, 80, 119, &
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84, 102, 135, &
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86, 105, 124, &
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4, 87, 128, &
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90, 106, 116, &
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65, 98, 130, &
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92, 108, 114, &
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1, 52, 121, &
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2, 84, 117, &
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5, 83, 105, &
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6, 15, 63, &
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7, 28, 82, &
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8, 32, 135, &
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9, 104, 134, &
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9, 10, 89, &
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12, 62, 107, &
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13, 40, 103, &
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14, 31, 95, &
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16, 27, 74, &
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17, 90, 132, &
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18, 34, 69, &
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19, 103, 129, &
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20, 76, 87, &
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21, 22, 130, &
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23, 25, 99, &
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24, 101, 126/
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data Nm/ &
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1, 47, 91, 140, 186, 0, &
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2, 48, 94, 141, 187, 0, &
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3, 47, 95, 142, 168, 0, &
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4, 49, 96, 143, 182, 0, &
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5, 50, 97, 144, 188, 0, &
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6, 51, 98, 145, 189, 0, &
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2, 52, 99, 146, 190, 0, &
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7, 53, 100, 143, 191, 0, &
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8, 54, 101, 147, 192, 193, &
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9, 55, 102, 148, 193, 0, &
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10, 56, 103, 149, 174, 0, &
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11, 57, 104, 150, 194, 0, &
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12, 58, 97, 151, 195, 0, &
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13, 59, 104, 152, 196, 0, &
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13, 60, 105, 153, 189, 0, &
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10, 61, 106, 151, 197, 0, &
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14, 62, 107, 154, 198, 0, &
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15, 63, 102, 155, 199, 0, &
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16, 64, 108, 156, 200, 0, &
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17, 47, 109, 137, 201, 0, &
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18, 65, 106, 157, 202, 0, &
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19, 56, 110, 156, 202, 0, &
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19, 62, 111, 141, 203, 0, &
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20, 51, 112, 136, 204, 0, &
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21, 66, 113, 158, 203, 0, &
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22, 67, 110, 159, 0, 0, &
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23, 68, 98, 160, 197, 0, &
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24, 69, 114, 161, 190, 0, &
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25, 70, 115, 126, 0, 0, &
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26, 71, 116, 162, 0, 0, &
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12, 72, 101, 161, 196, 0, &
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27, 73, 112, 163, 191, 0, &
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28, 74, 117, 164, 0, 0, &
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29, 50, 118, 165, 199, 0, &
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29, 75, 119, 139, 0, 0, &
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18, 53, 120, 154, 179, 0, &
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21, 69, 107, 144, 0, 0, &
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1, 76, 121, 166, 0, 0, &
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20, 58, 119, 154, 0, 0, &
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28, 77, 122, 167, 195, 0, &
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22, 59, 123, 168, 0, 0, &
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21, 78, 124, 169, 0, 0, &
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16, 79, 125, 145, 0, 0, &
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30, 80, 125, 140, 0, 0, &
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31, 62, 126, 170, 0, 0, &
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32, 68, 90, 150, 0, 0, &
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33, 63, 121, 153, 0, 0, &
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3, 52, 127, 171, 0, 0, &
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33, 80, 114, 157, 0, 0, &
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6, 57, 128, 169, 0, 0, &
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22, 81, 99, 172, 0, 0, &
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33, 46, 96, 139, 186, 0, &
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34, 58, 117, 173, 0, 0, &
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35, 82, 116, 158, 0, 0, &
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8, 83, 124, 156, 0, 0, &
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32, 69, 105, 149, 0, 0, &
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36, 65, 102, 158, 0, 0, &
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37, 68, 101, 165, 0, 0, &
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38, 79, 107, 173, 0, 0, &
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19, 84, 129, 161, 0, 0, &
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25, 78, 130, 168, 0, 0, &
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9, 71, 131, 174, 194, 0, &
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39, 85, 103, 155, 189, 0, &
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24, 57, 118, 175, 0, 0, &
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8, 86, 93, 166, 184, 0, &
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40, 70, 122, 174, 0, 0, &
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23, 84, 119, 176, 0, 0, &
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25, 60, 97, 148, 0, 0, &
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32, 87, 132, 173, 199, 0, &
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23, 64, 123, 144, 0, 0, &
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39, 54, 109, 120, 0, 0, &
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41, 49, 128, 137, 0, 0, &
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42, 88, 120, 175, 0, 0, &
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40, 86, 129, 162, 197, 0, &
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38, 49, 93, 151, 0, 0, &
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34, 65, 99, 177, 201, 0, &
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16, 48, 100, 178, 0, 0, &
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7, 59, 131, 170, 0, 0, &
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4, 50, 111, 152, 0, 0, &
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27, 87, 94, 179, 0, 0, &
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15, 74, 98, 142, 0, 0, &
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42, 67, 125, 148, 190, 0, &
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43, 61, 133, 164, 188, 0, &
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36, 84, 91, 180, 187, 0, &
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41, 72, 108, 172, 0, 0, &
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36, 77, 127, 181, 0, 0, &
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14, 55, 134, 182, 201, 0, &
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30, 52, 126, 149, 0, 0, &
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43, 48, 135, 159, 193, 0, &
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29, 61, 113, 183, 198, 0, &
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26, 64, 109, 164, 0, 0, &
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38, 74, 131, 163, 185, 0, &
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30, 72, 113, 163, 0, 0, &
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4, 87, 122, 140, 147, 0, &
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42, 76, 112, 171, 196, 0, &
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44, 60, 129, 143, 0, 0, &
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5, 81, 134, 162, 0, 0, &
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15, 88, 111, 184, 0, 0, &
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10, 46, 136, 167, 203, 0, &
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9, 75, 132, 169, 178, 0, &
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45, 55, 94, 160, 204, 0, &
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17, 70, 135, 180, 0, 0, &
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14, 89, 118, 146, 195, 200, &
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35, 73, 123, 177, 192, 0, &
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41, 82, 103, 181, 188, 0, &
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3, 90, 134, 170, 183, 0, &
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1, 82, 117, 141, 194, 0, &
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5, 91, 100, 136, 185, 0, &
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39, 77, 114, 160, 0, 0, &
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45, 66, 137, 153, 0, 0, &
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18, 90, 138, 166, 0, 0, &
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20, 85, 124, 152, 0, 0, &
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11, 73, 135, 157, 0, 0, &
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2, 54, 139, 185, 0, 0, &
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44, 85, 138, 146, 0, 0, &
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35, 53, 115, 183, 0, 0, &
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28, 66, 110, 138, 187, 0, &
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44, 75, 95, 167, 0, 0, &
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11, 79, 95, 179, 0, 0, &
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37, 92, 115, 155, 0, 0, &
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27, 56, 130, 165, 186, 0, &
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6, 81, 133, 147, 0, 0, &
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43, 88, 105, 176, 0, 0, &
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26, 78, 96, 175, 181, 0, &
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12, 71, 121, 159, 0, 0, &
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40, 63, 108, 150, 204, 0, &
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13, 93, 127, 178, 0, 0, &
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31, 83, 106, 182, 0, 0, &
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45, 92, 133, 171, 200, 0, &
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17, 51, 89, 184, 202, 0, &
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34, 86, 130, 145, 0, 0, &
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46, 92, 104, 177, 198, 0, &
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31, 76, 132, 172, 0, 0, &
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7, 80, 89, 176, 192, 0, &
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37, 67, 128, 180, 191, 0, &
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24, 83, 116, 142, 0, 0/
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data nrw/ &
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5,5,5,5,5,5,5,5,6,5,5,5,5,5,5,5,5, &
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5,5,5,5,5,5,5,5,4,5,5,4,4,5,5,4,5, &
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4,5,4,4,4,5,4,4,4,4,4,4,4,4,4,4,4, &
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5,4,4,4,4,4,4,4,4,4,5,5,4,5,4,4,4, &
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5,4,4,4,4,5,4,5,4,4,4,4,4,5,5,5,4, &
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4,5,4,5,5,4,5,4,5,5,4,4,4,5,5,5,4, &
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6,5,5,5,5,5,4,4,4,4,4,4,4,4,5,4,4, &
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4,5,4,4,5,4,5,4,4,5,5,4,5,4,5,5,4/
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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'
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enddo
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! write(*,*) 'number of unsatisfied parity checks ',ncheck
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if( ncheck .eq. 0 ) then ! we have a codeword - reorder the columns and return it
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codeword=cw(colorder+1)
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decoded=codeword(M+1:N)
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nerr=0
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do i=1,N
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if( (2*cw(i)-1)*llr(i) .lt. 0.0 ) nerr=nerr+1
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enddo
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nharderror=nerr
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return
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endif
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if( iter.gt.0 ) then ! this code block implements an early stopping criterion
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! if( iter.gt.10000 ) then ! this code block implements an early stopping criterion
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nd=ncheck-nclast
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if( nd .lt. 0 ) then ! # of unsatisfied parity checks decreased
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ncnt=0 ! reset counter
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else
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ncnt=ncnt+1
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endif
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! write(*,*) iter,ncheck,nd,ncnt
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if( ncnt .ge. 5 .and. iter .ge. 10 .and. ncheck .gt. 15) then
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nharderror=-1
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return
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endif
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endif
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nclast=ncheck
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! Send messages from bits to check nodes
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do j=1,M
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do i=1,nrw(j)
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ibj=Nm(i,j)
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toc(i,j)=zn(ibj)
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do kk=1,ncw ! subtract off what the bit had received from the check
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if( Mn(kk,ibj) .eq. j ) then
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toc(i,j)=toc(i,j)-tov(kk,ibj)
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endif
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enddo
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enddo
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enddo
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! send messages from check nodes to variable nodes
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do i=1,M
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tanhtoc(1:6,i)=tanh(-toc(1:6,i)/2)
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enddo
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do j=1,N
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do i=1,ncw
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ichk=Mn(i,j) ! Mn(:,j) are the checks that include bit j
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Tmn=product(tanhtoc(1:nrw(ichk),ichk),mask=Nm(1:nrw(ichk),ichk).ne.j)
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call platanh(-Tmn,y)
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! y=atanh(-Tmn)
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tov(i,j)=2*y
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enddo
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enddo
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enddo
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nharderror=-1
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return
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end subroutine bpdecode204
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