47 lines
1.2 KiB
Plaintext
47 lines
1.2 KiB
Plaintext
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subroutine encode_msk40(message,codeword)
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! Encode a 16-bit message and return a 32-bit codeword.
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! The code is a (32,16) regular ldpc code with column weight 3.
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! The code was generated using the PEG algorithm.
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! After creating the codeword, the columns are re-ordered according to
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! "colorder" to make the codeword compatible with the parity-check
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! matrix stored in Radford Neal's "pchk" format.
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!
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integer*1 codeword(32)
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integer*1 colorder(32)
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integer g(16)
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integer*1 gen40(16,16)
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integer*1 itmp(32)
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integer*1 message(16)
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integer*1 pchecks(16)
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logical first
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data first/.true./
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data g/Z'4428',Z'5a6b',Z'1b04',Z'2c12',Z'60c4',Z'1071',Z'be6a',Z'36dd', &
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Z'c580',Z'ad9a',Z'eca2',Z'7843',Z'332e',Z'a685',Z'5906',Z'1efe'/
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data colorder/4,1,2,3,0,8,6,10,13,28,20,23,17,15,27,25, &
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16,12,18,19,7,21,22,11,24,5,26,14,9,29,30,31/
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save first,gen40
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if( first ) then ! fill the generator matrix
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gen40=0
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do i=1,16
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do j=1,16
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if( btest(g(i),16-j) ) gen40(i,j)=1
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enddo
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enddo
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first=.false.
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endif
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do i=1,16
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nsum=0
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do j=1,16
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nsum=nsum+message(j)*gen40(i,j)
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enddo
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pchecks(i)=mod(nsum,2)
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enddo
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itmp(1:16)=pchecks
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itmp(17:32)=message(1:16)
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codeword(colorder+1)=itmp(1:32)
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return
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end subroutine encode_msk40
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