2017-06-13 20:45:44 -04:00
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subroutine encode174(message,codeword)
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2018-02-24 16:40:47 -05:00
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! Encode an 87-bit message and return a 174-bit codeword.
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! The generator matrix has dimensions (87,87).
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! The code is a (174,87) regular ldpc code with column weight 3.
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2017-06-13 20:45:44 -04:00
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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_174_87_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=1,11
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read(g(i)( (j-1)*2+1:(j-1)*2+2 ),"(Z2)") istr
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do jj=1, 8
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icol=(j-1)*8+jj
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if( icol .le. 87 ) then
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if( btest(istr,8-jj) ) gen(i,icol)=1
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endif
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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 encode174
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