WSJT-X/lib/ft8/encode174_91.f90

subroutine encode174_91(message77,codeword)
!
! Add a 14-bit CRC to a 77-bit message and return a 174-bit codeword
!
   use, intrinsic :: iso_c_binding
   use iso_c_binding, only: c_loc,c_size_t
   use crc

   integer, parameter:: N=174, K=91, M=N-K
   character*91 tmpchar
   integer*1 codeword(N)
   integer*1 gen(M,K)
   integer*1 message77(77),message(K)
   integer*1 pchecks(M)
   integer*1, target :: i1MsgBytes(12)
   include "ldpc_174_91_c_generator.f90"
   logical first
   data first/.true./
   save first,gen

   if( first ) then ! fill the generator matrix
      gen=0
      do i=1,M
         do j=1,23
            read(g(i)(j:j),"(Z1)") istr
            ibmax=4
            if(j.eq.23) ibmax=3
            do jj=1, ibmax
               icol=(j-1)*4+jj
               if( btest(istr,4-jj) ) gen(i,icol)=1
            enddo
         enddo
      enddo
      first=.false.
   endif

! Add 14-bit CRC to form 91-bit message+CRC14
   write(tmpchar,'(77i1)') message77
   tmpchar(78:80)='000'
   i1MsgBytes=0
   read(tmpchar,'(10b8)') i1MsgBytes(1:10)
   ncrc14 = crc14 (c_loc (i1MsgBytes), 12)
   write(tmpchar(78:91),'(b14)') ncrc14
   read(tmpchar,'(91i1)') message

   do i=1,M
      nsum=0
      do j=1,K
         nsum=nsum+message(j)*gen(i,j)
      enddo
      pchecks(i)=mod(nsum,2)
   enddo

   codeword(1:K)=message
   codeword(K+1:N)=pchecks

   return
end subroutine encode174_91