From 39aeb7a48c69cfa525a444143e9b02bc23554e88 Mon Sep 17 00:00:00 2001
From: Oliver Jowett <oliver@mutability.co.uk>
Date: Thu, 2 May 2019 18:19:27 +0800
Subject: [PATCH] Remove comm-b "consistency" bonuses, look at inconsistent
 data only.

Rescale penalties so badly inconsistent messages will tend to get
the same penalty in all formats, so the ambiguity check kicks in.

With this final change the HEADING_SPEED and TRACK_TURN message rates
are almost identical, which is what we'd expect to see if the
interrogator is asking for both at about the same rate.

Before:

    567 AMBIGUOUS
   7445 GICB_CAPS
  19173 EMPTY_RESPONSE
  75252 UNKNOWN
  76469 AIRCRAFT_IDENT
 127603 ACAS_RA
 212654 HEADING_SPEED
 223068 DATALINK_CAPS
 229807 TRACK_TURN
 269267 VERTICAL_INTENT
    466 "suspicious"

After:

   7445 GICB_CAPS
  17432 AMBIGUOUS
  19173 EMPTY_RESPONSE
  75252 UNKNOWN
  76469 AIRCRAFT_IDENT
 127603 ACAS_RA
 212718 HEADING_SPEED
 212878 TRACK_TURN
 223068 DATALINK_CAPS
 269267 VERTICAL_INTENT
    328 "suspicious"
---
 comm_b.c | 45 +++++++++++++++++----------------------------
 1 file changed, 17 insertions(+), 28 deletions(-)

diff --git a/comm_b.c b/comm_b.c
index 33bf361..196ec14 100644
--- a/comm_b.c
+++ b/comm_b.c
@@ -358,29 +358,24 @@ static int decodeBDS40(struct modesMessage *mm, bool store)
         return 0;
     }
 
-    // small bonuses for consistent data
-    if (mcp_valid && fms_valid && mcp_alt == fms_alt) {
-        score += 2;
-    }
-
-    if (baro_valid && baro_raw == 2132) {
-        // 1013.2mb, standard pressure
-        score += 2;
+    // small penalty for inconsistent data
+    if (mcp_valid && fms_valid && mcp_alt != fms_alt) {
+        score -= 4;
     }
 
     if (mcp_valid) {
         unsigned remainder = mcp_alt % 500;
-        if (remainder < 16 || remainder > 484) {
-            // mcp altitude is a multiple of 500
-            score += 2;
+        if (!(remainder < 16 || remainder > 484)) {
+            // mcp altitude is not a multiple of 500
+            score -= 4;
         }
     }
 
     if (fms_valid) {
         unsigned remainder = fms_alt % 500;
-        if (remainder < 16 || remainder > 484) {
-            // fms altitude is a multiple of 500
-            score += 2;
+        if (!(remainder < 16 || remainder > 484)) {
+            // fms altitude is not a multiple of 500
+            score -= 4;
         }
     }
 
@@ -544,13 +539,11 @@ static int decodeBDS50(struct modesMessage *mm, bool store)
         return 0;
     }
 
-    // small bonuses for consistent data
+    // small penalty for inconsistent data
     if (gs_valid && tas_valid) {
         int delta = abs((int)gs_valid - (int)tas_valid);
-        if (delta < 50) {
-            score += 5;
-        } else if (delta > 150) {
-            score -= 5;
+        if (delta > 150) {
+            score -= 6;
         }
     }
 
@@ -558,10 +551,8 @@ static int decodeBDS50(struct modesMessage *mm, bool store)
     if (roll_valid && tas_valid && tas > 0 && track_rate_valid) {
         double turn_rate = 68625 * tan(roll * M_PI / 180.0) / (tas * 20 * M_PI);
         double delta = fabs(turn_rate - track_rate);
-        if (delta < 0.5) {
-            score += 5;
-        } else if (delta > 2.0) {
-            score -= 5;
+        if (delta > 2.0) {
+            score -= 6;
         }
     }
 
@@ -704,16 +695,14 @@ static int decodeBDS60(struct modesMessage *mm, bool store)
         return 0;
     }
 
-    // small bonuses for consistent data
+    // small penalty for inconsistent data
 
     // Should check IAS vs Mach at given altitude, but the maths is a little involved
 
     if (baro_rate_valid && inertial_rate_valid) {
         int delta = abs(baro_rate - inertial_rate);
-        if (delta < 500) {
-            score += 5;
-        } else if (delta > 2000) {
-            score -= 5;
+        if (delta > 2000) {
+            score -= 12;
         }
     }