WSJT-X/lib/fsk4hf/encode4K25A.f90

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2018-09-08 17:50:15 -04:00
subroutine encode4K25A(message,codeword)
! A (280,70) rate 1/4 tailbiting convolutional code using
! the "4K25A" polynomials from EbNaut website.
! Code is transparent, has constraint length 25, and has dmin=58
character*10 g1,g2,g3,g4
integer*1 codeword(280)
!integer*1 p1(25),p2(25),p3(25),p4(25)
integer*1 p1(16),p2(16),p3(16),p4(16)
integer*1 gg(100)
integer*1 gen(280,70)
integer*1 itmp(280)
integer*1 message(70)
logical first
data first/.true./
data g1/"106042635"/
data g2/"125445117"/
data g3/"152646773"/
data g4/"167561761"/
!data p1/1,0,0,0,1,1,0,0,0,0,1,0,0,0,1,0,1,1,0,0,1,1,1,0,1/
!data p2/1,0,1,0,1,0,1,1,0,0,1,0,0,1,0,1,0,0,1,0,0,1,1,1,1/
!data p3/1,1,0,1,0,1,0,1,1,0,1,0,0,1,1,0,1,1,1,1,1,1,0,1,1/
!data p4/1,1,1,0,1,1,1,1,0,1,1,1,0,0,0,1,1,1,1,1,1,0,0,0,1/
data p1/1,0,1,0,1,1,0,0,1,1,0,1,1,1,1,1/
data p2/1,0,1,1,0,1,0,0,1,1,1,1,1,0,0,1/
data p3/1,1,0,0,1,0,1,1,0,1,1,1,0,0,1,1/
data p4/1,1,1,0,1,1,0,1,1,1,1,0,0,1,0,1/
save first,gen
if( first ) then ! fill the generator matrix
gg=0
! gg(1:25)=p1
! gg(26:50)=p2
! gg(51:75)=p3
! gg(76:100)=p4
gg(1:16)=p1
gg(17:32)=p2
gg(33:48)=p3
gg(49:64)=p4
gen=0
! gen(1:100,1)=gg(1:100)
gen(1:64,1)=gg(1:64)
do i=2,70
gen(:,i)=cshift(gen(:,i-1),-4,1)
enddo
first=.false.
endif
codeword=0
do i=1,70
if(message(i).eq.1) codeword=codeword+gen(:,i)
enddo
codeword=mod(codeword,2)
return
end subroutine encode4K25A