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b39f92926c
git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/wsjtx@7633 ab8295b8-cf94-4d9e-aec4-7959e3be5d79
307 lines
7.2 KiB
Fortran
307 lines
7.2 KiB
Fortran
subroutine bpdecode120(llr,apmask,maxiterations,decoded,niterations,cw)
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! A log-domain belief propagation decoder for the (120,60) code.
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integer, parameter:: N=120, K=60, 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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0,1,2,21,3,4,5,6,7,8,20,10,9,11,12,23,13,28,14,31, &
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15,16,22,26,17,30,18,29,25,32,41,34,19,33,27,36,38,43,42,24, &
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37,39,45,40,35,44,47,46,50,51,53,48,52,56,54,57,55,49,58,61, &
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60,59,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79, &
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80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99, &
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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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data Mn/ &
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1, 18, 48, &
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2, 4, 51, &
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3, 23, 47, &
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5, 36, 42, &
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6, 43, 49, &
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7, 24, 55, &
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8, 35, 60, &
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9, 26, 30, &
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10, 29, 45, &
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11, 13, 46, &
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12, 53, 54, &
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14, 20, 57, &
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15, 16, 58, &
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17, 39, 44, &
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19, 37, 41, &
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21, 28, 34, &
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22, 50, 59, &
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25, 31, 52, &
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27, 32, 38, &
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33, 40, 56, &
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1, 11, 47, &
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2, 10, 16, &
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3, 12, 27, &
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4, 24, 28, &
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5, 23, 60, &
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6, 29, 39, &
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7, 31, 54, &
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8, 50, 56, &
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9, 13, 14, &
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15, 22, 41, &
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17, 26, 40, &
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18, 25, 45, &
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19, 20, 55, &
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21, 30, 36, &
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32, 49, 59, &
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33, 53, 58, &
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34, 38, 46, &
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29, 35, 57, &
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37, 43, 48, &
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42, 51, 52, &
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7, 11, 44, &
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1, 42, 58, &
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2, 13, 49, &
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3, 20, 40, &
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4, 18, 56, &
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5, 45, 55, &
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6, 21, 31, &
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8, 46, 52, &
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9, 12, 48, &
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10, 37, 38, &
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14, 15, 25, &
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16, 17, 60, &
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19, 39, 53, &
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22, 44, 51, &
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23, 28, 41, &
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24, 32, 35, &
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26, 45, 59, &
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27, 33, 36, &
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30, 47, 54, &
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34, 50, 57, &
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33, 43, 55, &
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1, 41, 57, &
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2, 40, 54, &
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3, 6, 24, &
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4, 11, 59, &
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5, 13, 56, &
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7, 16, 34, &
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8, 19, 26, &
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9, 31, 58, &
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10, 21, 53, &
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12, 22, 60, &
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14, 38, 51, &
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15, 43, 46, &
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17, 48, 50, &
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18, 27, 39, &
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20, 28, 44, &
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23, 25, 49, &
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4, 29, 36, &
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30, 32, 52, &
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35, 37, 47, &
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39, 42, 59, &
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1, 21, 40, &
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2, 50, 55, &
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3, 8, 10, &
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5, 31, 37, &
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6, 14, 60, &
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7, 36, 49, &
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9, 34, 39, &
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11, 19, 25, &
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12, 52, 57, &
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13, 22, 29, &
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15, 30, 56, &
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16, 18, 20, &
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17, 24, 46, &
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23, 38, 58, &
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26, 28, 43, &
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2, 27, 41, &
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5, 32, 44, &
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33, 47, 51, &
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35, 48, 53, &
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42, 43, 54, &
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34, 45, 47, &
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1, 8, 49, &
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3, 14, 59, &
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4, 31, 46, &
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6, 20, 50, &
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7, 26, 53, &
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9, 10, 36, &
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11, 58, 60, &
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12, 21, 45, &
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13, 28, 33, &
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15, 17, 35, &
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16, 38, 52, &
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18, 41, 54, &
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19, 23, 32, &
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22, 40, 55, &
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24, 25, 42, &
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26, 27, 56, &
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29, 44, 54, &
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30, 37, 55/
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data Nm/ &
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1, 21, 42, 62, 82, 103, 0, &
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2, 22, 43, 63, 83, 97, 0, &
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3, 23, 44, 64, 84, 104, 0, &
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2, 24, 45, 65, 78, 105, 0, &
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4, 25, 46, 66, 85, 98, 0, &
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5, 26, 47, 64, 86, 106, 0, &
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6, 27, 41, 67, 87, 107, 0, &
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7, 28, 48, 68, 84, 103, 0, &
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8, 29, 49, 69, 88, 108, 0, &
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9, 22, 50, 70, 84, 108, 0, &
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10, 21, 41, 65, 89, 109, 0, &
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11, 23, 49, 71, 90, 110, 0, &
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10, 29, 43, 66, 91, 111, 0, &
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12, 29, 51, 72, 86, 104, 0, &
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13, 30, 51, 73, 92, 112, 0, &
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13, 22, 52, 67, 93, 113, 0, &
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14, 31, 52, 74, 94, 112, 0, &
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1, 32, 45, 75, 93, 114, 0, &
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15, 33, 53, 68, 89, 115, 0, &
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12, 33, 44, 76, 93, 106, 0, &
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16, 34, 47, 70, 82, 110, 0, &
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17, 30, 54, 71, 91, 116, 0, &
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3, 25, 55, 77, 95, 115, 0, &
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6, 24, 56, 64, 94, 117, 0, &
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18, 32, 51, 77, 89, 117, 0, &
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8, 31, 57, 68, 96, 107, 118, &
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19, 23, 58, 75, 97, 118, 0, &
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16, 24, 55, 76, 96, 111, 0, &
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9, 26, 38, 78, 91, 119, 0, &
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8, 34, 59, 79, 92, 120, 0, &
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18, 27, 47, 69, 85, 105, 0, &
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19, 35, 56, 79, 98, 115, 0, &
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20, 36, 58, 61, 99, 111, 0, &
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16, 37, 60, 67, 88, 102, 0, &
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7, 38, 56, 80, 100, 112, 0, &
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4, 34, 58, 78, 87, 108, 0, &
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15, 39, 50, 80, 85, 120, 0, &
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19, 37, 50, 72, 95, 113, 0, &
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14, 26, 53, 75, 81, 88, 0, &
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20, 31, 44, 63, 82, 116, 0, &
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15, 30, 55, 62, 97, 114, 0, &
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4, 40, 42, 81, 101, 117, 0, &
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5, 39, 61, 73, 96, 101, 0, &
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14, 41, 54, 76, 98, 119, 0, &
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9, 32, 46, 57, 102, 110, 0, &
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10, 37, 48, 73, 94, 105, 0, &
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3, 21, 59, 80, 99, 102, 0, &
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1, 39, 49, 74, 100, 0, 0, &
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5, 35, 43, 77, 87, 103, 0, &
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17, 28, 60, 74, 83, 106, 0, &
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2, 40, 54, 72, 99, 0, 0, &
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18, 40, 48, 79, 90, 113, 0, &
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11, 36, 53, 70, 100, 107, 0, &
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11, 27, 59, 63, 101, 114, 119, &
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6, 33, 46, 61, 83, 116, 120, &
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20, 28, 45, 66, 92, 118, 0, &
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12, 38, 60, 62, 90, 0, 0, &
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13, 36, 42, 69, 95, 109, 0, &
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17, 35, 57, 65, 81, 104, 0, &
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7, 25, 52, 71, 86, 109, 0/
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data nrw/ &
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6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6, &
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6,6,6,6,6,7,6,6,6,6,6,6,6,6,6,6,6,6,6,6, &
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6,6,6,6,6,6,6,5,6,6,5,6,6,7,7,6,5,6,6,6/
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ncw=3
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toc=0
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tov=0
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tanhtoc=0
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!write(*,*) llr
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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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niterations=iter
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codeword=cw(colorder+1)
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decoded=codeword(M+1:N)
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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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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. 3 .and. iter .ge. 5 .and. ncheck .gt. 10) then
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niterations=-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(1:7,i)=tanh(-toc(1:7,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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niterations=-1
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return
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end subroutine bpdecode120
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