From 7fd931ae5f6f5b35ad0c090d6f5b4a1757af7c54 Mon Sep 17 00:00:00 2001
From: Zilog80 <rs1729@users.noreply.github.com>
Date: Fri, 1 May 2020 14:27:47 +0200
Subject: [PATCH] Hamming [8,4] 2-bit-errors -> soft decision

---
 demod/mod/dfm09mod.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/demod/mod/dfm09mod.c b/demod/mod/dfm09mod.c
index f101a37..a5216eb 100644
--- a/demod/mod/dfm09mod.c
+++ b/demod/mod/dfm09mod.c
@@ -195,9 +195,12 @@ static int check(int opt_ecc, hsbit_t code[8]) {
         int d = 0;
         float sum = 0.0;
         float maxsum = 0.0;
-        for (i = 0; i < 8; i++) {
-            sum += (2*code[i].hb-1) * code[i].sb;
-        }
+        /*
+        sum = 0.0;                 // s<0: h=0 , s>0: h=1
+        for (i = 0; i < 8; i++) {  // s\in[-1,+1] , h\in{0,1} -> 2h-1\in{-1,+1}
+            sum += (2*code[i].hb-1)*code[i].sb;  // i.e. sum_i |sb_i|
+        } // original score
+        */
         for (n = 0; n < 16; n++) {
             d = 0;
             sum = 0.0;
@@ -211,7 +214,7 @@ static int check(int opt_ecc, hsbit_t code[8]) {
                 for (i = 0; i < 8; i++) {
                     sum += (2*codewords[n][i]-1) * code[i].sb;
                 }
-                if (sum*sum >= maxsum*maxsum) {
+                if (sum >= maxsum) { // best match
                     maxsum = sum;
                     maxn = n;
                 }