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49 lines
1.0 KiB
Fortran
49 lines
1.0 KiB
Fortran
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subroutine encode204(message,codeword)
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! Encode an 68-bit message and return a 204-bit codeword.
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! The generator matrix has dimensions (136,68).
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! The code is a (204,68) 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 matrix
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!
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include "ldpc_204_68_params.f90"
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integer*1 codeword(N)
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integer*1 gen(M,K)
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integer*1 itmp(N)
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integer*1 message(K)
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integer*1 pchecks(M)
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logical first
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data first/.true./
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save first,gen
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if( first ) then ! fill the generator matrix
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gen=0
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do i=1,M
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do j=1,17
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read(g(i)(j:j),"(Z1)") istr
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do jj=1, 4
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icol=(j-1)*4+jj
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if( btest(istr,4-jj) ) gen(i,icol)=1
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enddo
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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,M
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nsum=0
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do j=1,K
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nsum=nsum+message(j)*gen(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:M)=pchecks
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itmp(M+1:N)=message(1:K)
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codeword(colorder+1)=itmp(1:N)
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return
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end subroutine encode204
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