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60 lines
1.3 KiB
Fortran
60 lines
1.3 KiB
Fortran
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subroutine bitflip128_90(llr,message77,cw,nharderror)
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!
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! A hard-decision bit flipping decoder for the (128,90) code.
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!
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use iso_c_binding, only: c_loc,c_size_t
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use crc
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integer, parameter:: N=128, K=90, M=N-K
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integer*1 cw(N),apmask(N)
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integer*1 decoded(K)
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integer*1 message77(77)
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integer Nm(11,M)
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integer Mn(3,N)
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integer nrw(M)
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integer synd(M)
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integer nuns(N)
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real zn(N)
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real llr(N)
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include "ldpc_128_90_reordered_parity.f90"
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decoded=0
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zn=llr
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do iter=0,0
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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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nuns=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 ) then
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ncheck=ncheck+1
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do j=1,nrw(i)
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nuns(Nm(j,i))=nuns(Nm(j,i))+1
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enddo
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endif
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enddo
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if( ncheck .eq. 0 ) then ! we have a codeword - reorder the columns and return it
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decoded=cw(1:K)
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call chkcrc13a(decoded,nbadcrc)
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if(nbadcrc.eq.0) then
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message77=decoded(1:77)
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nharderror=count( (2*cw-1)*llr .lt. 0.0 )
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return
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endif
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endif
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! flip the sign on the symbols that show up in the largest number
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! of un-satisfied parity checks
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where( nuns .eq. maxval(nuns) ) zn=-zn
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enddo
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llr=zn
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nharderror=-1
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return
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end subroutine bitflip128_90
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