From 8b8f8d7a4038e9ca248a0ce232fb66ada1decb1a Mon Sep 17 00:00:00 2001
From: Oliver Jowett <oliver@mutability.co.uk>
Date: Fri, 26 Aug 2016 21:38:06 +0100
Subject: [PATCH] Use INVALID_ALTITUDE in a few more places.

---
 dump1090.h |  2 ++
 mode_ac.c  | 16 +++++++++-------
 mode_s.c   |  2 --
 3 files changed, 11 insertions(+), 9 deletions(-)

diff --git a/dump1090.h b/dump1090.h
index d98353e..89ca13d 100644
--- a/dump1090.h
+++ b/dump1090.h
@@ -167,6 +167,8 @@ typedef struct rtlsdr_dev rtlsdr_dev_t;
 #define MODES_ACFLAGS_LLBOTH_VALID   (MODES_ACFLAGS_LLEVEN_VALID | MODES_ACFLAGS_LLODD_VALID)
 #define MODES_ACFLAGS_AOG_GROUND     (MODES_ACFLAGS_AOG_VALID    | MODES_ACFLAGS_AOG)
 
+#define INVALID_ALTITUDE (-9999)
+
 #define MODES_NON_ICAO_ADDRESS       (1<<24) // Set on addresses to indicate they are not ICAO addresses
 
 #define MODES_DEBUG_DEMOD (1<<0)
diff --git a/mode_ac.c b/mode_ac.c
index 0473014..02ad281 100644
--- a/mode_ac.c
+++ b/mode_ac.c
@@ -35,13 +35,14 @@
 // Input format is : 00:A4:A2:A1:00:B4:B2:B1:00:C4:C2:C1:00:D4:D2:D1
 //
 int ModeAToModeC(unsigned int ModeA) 
-  { 
+{
   unsigned int FiveHundreds = 0;
   unsigned int OneHundreds  = 0;
 
-  if (  (ModeA & 0xFFFF8889)         // check zero bits are zero, D1 set is illegal
-    || ((ModeA & 0x000000F0) == 0) ) // C1,,C4 cannot be Zero
-    {return -9999;}
+  if ((ModeA & 0xFFFF8889) != 0 ||         // check zero bits are zero, D1 set is illegal
+      (ModeA & 0x000000F0) == 0) { // C1,,C4 cannot be Zero
+      return INVALID_ALTITUDE;
+  }
 
   if (ModeA & 0x0010) {OneHundreds ^= 0x007;} // C1
   if (ModeA & 0x0020) {OneHundreds ^= 0x003;} // C2
@@ -51,8 +52,9 @@ int ModeAToModeC(unsigned int ModeA)
   if ((OneHundreds & 5) == 5) {OneHundreds ^= 2;}
 
   // Check for invalid codes, only 1 to 5 are valid 
-  if (OneHundreds > 5)
-    {return -9999;} 
+  if (OneHundreds > 5) {
+      return INVALID_ALTITUDE;
+  }
 
 //if (ModeA & 0x0001) {FiveHundreds ^= 0x1FF;} // D1 never used for altitude
   if (ModeA & 0x0002) {FiveHundreds ^= 0x0FF;} // D2
@@ -70,7 +72,7 @@ int ModeAToModeC(unsigned int ModeA)
   if (FiveHundreds & 1) {OneHundreds = 6 - OneHundreds;} 
 
   return ((FiveHundreds * 5) + OneHundreds - 13); 
-  } 
+}
 //
 //=========================================================================
 //
diff --git a/mode_s.c b/mode_s.c
index 574cb0f..8e9e355 100644
--- a/mode_s.c
+++ b/mode_s.c
@@ -111,8 +111,6 @@ static int decodeID13Field(int ID13Field) {
     return (hexGillham);
 }
 
-#define INVALID_ALTITUDE (-9999)
-
 //
 //=========================================================================
 //