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subroutine encode174(message,codeword)
! Encode an 87-bit message and return a 174-bit codeword.
! The generator matrix has dimensions (87,87).
! The code is a (174,87) regular ldpc code with column weight 3.
! The code was generated using the PEG algorithm.
! After creating the codeword, the columns are re-ordered according to
! "colorder" to make the codeword compatible with the parity-check matrix
!
include "ldpc_174_87_params.f90"
integer*1 codeword(N)
integer*1 gen(M,K)
integer*1 itmp(N)
integer*1 message(K)
integer*1 pchecks(M)
logical first
data first/.true./
save first,gen
if( first ) then ! fill the generator matrix
gen=0
do i=1,M
do j=1,11
read(g(i)( (j-1)*2+1:(j-1)*2+2 ),"(Z2)") istr
do jj=1, 8
icol=(j-1)*8+jj
if( icol .le. 87 ) then
if( btest(istr,8-jj) ) gen(i,icol)=1
endif
enddo
enddo
enddo
first=.false.
endif
do i=1,M
nsum=0
do j=1,K
nsum=nsum+message(j)*gen(i,j)
enddo
pchecks(i)=mod(nsum,2)
enddo
itmp(1:M)=pchecks
itmp(M+1:N)=message(1:K)
codeword(colorder+1)=itmp(1:N)
return
end subroutine encode174
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