From cd7f0c16c4effecf2345fb740ce7e617a1471485 Mon Sep 17 00:00:00 2001
From: f4exb <f4exb06@gmail.com>
Date: Sat, 6 Apr 2024 10:46:39 +0200
Subject: [PATCH] FT8: implement Gray decoding when decoding from magnitudes

---
 ft8/ft8.cpp                    | 29 ++++++++++++++++++++++++++++-
 ft8/ft8.h                      |  5 +++++
 sdrbench/test_ft8protocols.cpp |  3 ++-
 3 files changed, 35 insertions(+), 2 deletions(-)

diff --git a/ft8/ft8.cpp b/ft8/ft8.cpp
index a64911f60..a3c6a8397 100644
--- a/ft8/ft8.cpp
+++ b/ft8/ft8.cpp
@@ -1233,6 +1233,32 @@ std::vector<std::vector<float>> FT8::un_gray_code_r(const std::vector<std::vecto
     return m79a;
 }
 
+//
+// Generic Gray decoding for magnitudes (floats)
+//
+std::vector<std::vector<float>> FT8::un_gray_code_r_gen(const std::vector<std::vector<float>> &mags)
+{
+    if (mags.size() == 0) {
+        return mags;
+    }
+
+    std::vector<std::vector<float>> magsa(mags.size());
+    int nsyms = mags.front().size();
+
+    for (unsigned int si = 0; si < mags.size(); si++)
+    {
+        magsa[si].resize(nsyms);
+
+        for (int bini = 0; bini < nsyms; bini++)
+        {
+            int grayi = bini ^ (bini >> 1);
+            magsa[si][bini] = mags[si][grayi];
+        }
+    }
+
+    return magsa;
+}
+
 //
 // normalize levels by windowed median.
 // this helps, but why?
@@ -1919,6 +1945,7 @@ void FT8::soft_decode_mags(FT8Params& params, const std::vector<std::vector<floa
     Stats bests(params.problt_how_sig, params.log_tail, params.log_rate);
     Stats all(params.problt_how_noise, params.log_tail, params.log_rate);
     make_stats_gen(mags, nbSymbolBits, bests, all);
+    mags = un_gray_code_r_gen(mags);
     int lli = 0;
     int zoX = 1<<(nbSymbolBits-1);
     int zoY = nbSymbolBits;
@@ -3188,7 +3215,7 @@ int FT8::one_iter1(
             hz1_for_cb,
             params.use_osd,
             "",
-             m79
+            m79
         );
 
         if (ret) {
diff --git a/ft8/ft8.h b/ft8/ft8.h
index 004e411ea..d381d6d0c 100644
--- a/ft8/ft8.h
+++ b/ft8/ft8.h
@@ -286,6 +286,11 @@ public:
     //
     static void soft_decode_mags(FT8Params& params, const std::vector<std::vector<float>>& mags, int nbSymbolBits, float ll174[]);
 
+    //
+    // Generic Gray decoding for magnitudes (floats)
+    //
+    static std::vector<std::vector<float>> un_gray_code_r_gen(const std::vector<std::vector<float>> &mags);
+
 private:
     //
     // reduce the sample rate from arate to brate.
diff --git a/sdrbench/test_ft8protocols.cpp b/sdrbench/test_ft8protocols.cpp
index b5cdc4d41..573259c75 100644
--- a/sdrbench/test_ft8protocols.cpp
+++ b/sdrbench/test_ft8protocols.cpp
@@ -322,7 +322,8 @@ void TestFT8Protocols::testSoftDecode(const QStringList& argElements)
         }
 
         symbol = symbol % symbolSize;
-        magSymbols[symbol] += 0.01;
+        symbol = symbol ^(symbol >> 1); // Gray code
+        magSymbols[symbol] += 0.015;
         mags.push_back(magSymbols);
     }