Refine a test program and add comments.

git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/wsjtx@8203 ab8295b8-cf94-4d9e-aec4-7959e3be5d79

lib/fsk4hf/jt65osdtest.f90

@@ -1,32 +1,59 @@
 program jt65osdtest
 !
-! Test k9an's JT65 encoder by comparing codewords with 
+! Demonstrate some procedures that can be used to implement an ordered-
+! statistics decoder for JT65. 
+! 1. Test JT65 generator-matrix-based encoding by comparing codewords with 
 ! those produced by the tried-and-true KA9Q encoder
+! 2. Demonstrate how to reconfigure the generator matrix to make an arbitrary
+! subset of 12 symbols the systematic symbols, and show that re-encoding using
+! the subset of symbols regenerates the original codeword.
 !
    use jt65_generator_matrix
    use gf64math
+   use packjt
 
+   character*22 message    
    integer m(12),cwka9q(63),cwk9an(63),cwtest(63)
    integer gmrb(12,63)
-   do i=1,12
-      m(i)=i
-   enddo
+   data m/61,51,10,42,51,55, 3,29,53,55,58,42/ !"K9AN K1JT -25"
+
+   message="K9AN K1JT RRR"
+   call packmsg(message,m,itype,.false.)
+   write(*,*) 'Message text: ',message
+   write(*,*) 'Message symbols:'
+   write(*,'(12i3)') m
+
+! Encode using Karn encoder.
    call rs_encode(m,cwka9q)
+   write(*,*) 'KA9Q codeword'
    write(*,'(63i3)') cwka9q 
+! Encode using generator matrix.
    call gf64_encode(g,m,cwk9an)
+   write(*,*) 'K9AN codeword'
    write(*,'(63i3)') cwk9an 
 
+! The message symbols are the last 12 symbols of the codeword. For this test,
+! "pretend" that the symbols at positions 1,3,5,7,9,11,13,15,17,19,21,23 are 
+! the best received symbols, i.e. the best symbols are all parity symbols.  
+! Reorder columns of the generator matrix so that the best symbols are in front
+! and then use Gauss-Jordan elimination to create a generator matrix that
+! can be used to re-encode the best 12 symbols, producing the same codeword
+! that we started with. 
    gmrb=g
-   call gf64_standardize_genmat(gmrb)
    do i=1,12
-      write(*,'(63i3)') gmrb(i,:)
+      gmrb(1:12,i)=g(1:12,2*i-1)
+      gmrb(1:12,i+12)=g(1:12,2*i)
    enddo
 
-   m(1:12)=cwk9an(1:12)
-   call gf64_encode(gmrb,m,cwtest)
-   write(*,*) 'Test message:'
+   call gf64_standardize_genmat(gmrb)
+
+! Now demonstrate that we can use the revised generator matrix to encode the 12
+! best symbols and recover the codeword that we started with.
+   m(1:12)=cwk9an(1:23:2)          !Take symbols 1,3,5,...23 as the message 
+   call gf64_encode(gmrb,m,cwtest) !reencode using the revised generator matrix
+   write(*,*) 'Re-encode using generator matrix reconfigured to use odd-index symbols starting at 1 as the message:'
    write(*,'(12i3)') m 
-   write(*,*) 'Codeword:'
-   write(*,'(63i3)') cwtest
+   write(*,*) 'Re-encoded codeword should be the same as the original codeword:'
+   write(*,'(63i3)') cwtest        !This should be the same as the original cw.
 
 end program jt65osdtest