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