From 45ba25f6edc0240d492ed04b2510a54efa8a8863 Mon Sep 17 00:00:00 2001
From: Steven Franke <s.j.franke@icloud.com>
Date: Sun, 24 Apr 2016 15:08:57 +0000
Subject: [PATCH] Add code needed to unpack decoded message.

git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/wsjtx@6645 ab8295b8-cf94-4d9e-aec4-7959e3be5d79
---
 lib/ldpcsim.f90 | 52 +++++++++++++++++++++++++++++++------------------
 1 file changed, 33 insertions(+), 19 deletions(-)

diff --git a/lib/ldpcsim.f90 b/lib/ldpcsim.f90
index 607a1de96..1904ed197 100644
--- a/lib/ldpcsim.f90
+++ b/lib/ldpcsim.f90
@@ -7,8 +7,8 @@ use, intrinsic :: iso_c_binding
 use hashing
 use packjt
 
-character*22 msg,msgsent
-integer*4 i4Msg6BitWords(12)
+character*22 msg,msgsent,msgreceived
+integer*4 i4Msg6BitWords(12),i4Dec6BitWords(12)
 integer*1, target:: i1Msg8BitBytes(10) ! 72 bit msg + 8 bit hash
 integer*1, target:: i1Dec8BitBytes(10) ! 72 bit msg + 8 bit hash
 integer*1 i1hashdec
@@ -22,8 +22,8 @@ equivalence (ihash,i1hash)
 
 nargs=iargc()
 if(nargs.ne.7) then
-   print*,'Usage: ldpcsim pchk/gen file prefix  N  K  niter ndither #trials  s '
-   print*,'eg:    ldpcsim  "128-80-peg-reg3"   128 80  10     1     1000    0.75'
+   print*,'Usage: ldpcsim  <pchk file prefix      >  N   K  niter ndither #trials  s '
+   print*,'eg:    ldpcsim  "/pathto/128-80-peg-reg3" 128 80  10     1     1000    0.75'
    return
 endif
 call getarg(1,prefix)
@@ -43,7 +43,7 @@ read(arg,*) s
 pchk_file=trim(prefix)//".pchk"
 gen_file=trim(prefix)//".gen"
 
-!rate=real(K)/real(N)
+! rate=real(K)/real(N)
 ! don't count hash bits as data bits
 rate=72.0/real(N)
 
@@ -54,7 +54,7 @@ allocate ( codeword(N), decoded(K), message(K) )
 allocate ( lratio(N), rxdata(N) )
 call init_ldpc(trim(pchk_file)//char(0),trim(gen_file)//char(0))
 
-msg="K1JT K9AN EN50"
+msg="123"
 call fmtmsg(msg,iz)
 call packmsg(msg,i4Msg6BitWords,itype)
 call unpackmsg(i4Msg6BitWords,msgsent)
@@ -104,19 +104,19 @@ do idb = 0, 11
 
   do itrial=1, ntrials
 
-! create a realization of a noisy received word
+! Create a realization of a noisy received word
     do i=1,N
       rxdata(i) = 2.0*(codeword(i)-0.5) + sigma*gran()
     enddo
 
-! correct signal normalization is important for this decoder.
+! Correct signal normalization is important for this decoder.
     rxav=sum(rxdata)/N
     rx2av=sum(rxdata*rxdata)/N
     rxsig=sqrt(rx2av-rxav*rxav)
     rxdata=rxdata/rxsig
 
 ! To match the metric to the channel, s should be set to the noise standard deviation. 
-! For now we just set s to the value that optimizes decode probability near threshold. 
+! For now, set s to the value that optimizes decode probability near threshold. 
 ! The s parameter can be tuned to trade a few tenth's dB of threshold for an order of
 ! magnitude in UER 
     do i=1,N
@@ -128,18 +128,16 @@ do idb = 0, 11
       lratio(i)=exp(2.0*rxdata(i)/(ss*ss))
     enddo
 
-! call interface to Radford Neal implementation of binary belief propagation.
 ! max_iterations is max number of belief propagation iterations
-! max_dither is the number of tries - try number 2 and beyond start with dithered likelihood ratios.
     call ldpc_decode(lratio, decoded, max_iterations, niterations, max_dither, ndither)
 
-! if the decoder finds a valid codeword, niterations will be .ge. 0
+! If the decoder finds a valid codeword, niterations will be .ge. 0.
     if( niterations .ge. 0 ) then
       nueflag=0
       nhashflag=0
-! the decoder produced a codeword --- compare hash part of message (byte 10) with computed hash 
-! first collapse 80 decoded bits to 10 bytes
-! the first 9 bytes are the message, 10'th byte is the hash.
+
+! The decoder found a codeword. Compare received hash (byte 10) with computed hash.
+! Collapse 80 decoded bits to 10 bytes. Bytes 1-9 are the message, byte 10 is the hash.
       do ibyte=1,10
         itmp=0
         do ibit=1,8
@@ -147,17 +145,19 @@ do idb = 0, 11
         enddo
         i1Dec8BitBytes(ibyte)=itmp
       enddo
-! calculate the hash using the first 9 bytes
+
+! Calculate the hash using the first 9 bytes.
       ihashdec=nhash(c_loc(i1Dec8BitBytes),int(9,c_size_t),146)
       ihashdec=2*iand(ihashdec,255)
-! compare calculated hash with received byte 10 - if they agree, keep the message
+
+! Compare calculated hash with received byte 10 - if they agree, keep the message.
       i1hashdec=ihashdec
       if( i1hashdec .ne. i1Dec8BitBytes(10) ) then
         nbadhash=nbadhash+1
         nhashflag=1   
       endif
 
-! check the message plus hash against what was sent
+! Check the message plus hash against what was sent.
       do i=1,K
         if( message(i) .ne. decoded(i) ) then
           nueflag=1
@@ -166,11 +166,25 @@ do idb = 0, 11
 
       if( nhashflag .eq. 0 .and. nueflag .eq. 0 ) then
         ngood=ngood+1
+
+! don't bother to unpack while testing
+if( .false. ) then
+! unpack 72-bit message
+        do ibyte=1,12
+          itmp=0
+          do ibit=1,6
+            itmp=ishft(itmp,1)+iand(1,decoded((ibyte-1)*6+ibit))
+          enddo
+          i4Dec6BitWords(ibyte)=itmp
+        enddo
+        call unpackmsg(i4Dec6BitWords,msgreceived)
+        print*,"Received ",msgreceived
+endif
+
       else if( nhashflag .eq. 0 .and. nueflag .eq. 1 ) then
         nue=nue+1;
       endif
     endif
-
   enddo
 
   write(*,"(f4.1,1x,i8,1x,i8,1x,i8)") db,ngood,nue,nbadhash