WSJT-X/lib/encode_msk40.f90
Steven Franke 011056e002 Actually add the new routines. When will I learn?
git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/wsjtx@7023 ab8295b8-cf94-4d9e-aec4-7959e3be5d79
2016-08-11 19:27:28 +00:00

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