Switch FMS/MCP altitudes to signed ints.

These altitudes can be negative in DO-260A (v1) Target State and Status
messages; previously we'd accidentally cast those to unsigned, producing a
bogus large positive altitude.

Author: mutability

dump1090.h

@@ -628,8 +628,8 @@ struct modesMessage {
 
         float    heading;       // heading, degrees (0-359) (could be magnetic or true heading; magnetic recommended)
         heading_type_t heading_type;
-        unsigned fms_altitude;  // FMS selected altitude
-        unsigned mcp_altitude;  // MCP/FCU selected altitude
+        int      fms_altitude;  // FMS selected altitude
+        int      mcp_altitude;  // MCP/FCU selected altitude
         float    qnh;           // altimeter setting (QFE or QNH/QNE), millibars
 
         nav_altitude_source_t altitude_source;

mode_s.c

@@ -2212,9 +2212,9 @@ void displayModesMessage(struct modesMessage *mm) {
     if (mm->nav.heading_valid)
         printf("  Selected heading:        %.1f\n", mm->nav.heading);
     if (mm->nav.fms_altitude_valid)
-        printf("  FMS selected altitude:   %u ft\n", mm->nav.fms_altitude);
+        printf("  FMS selected altitude:   %d ft\n", mm->nav.fms_altitude);
     if (mm->nav.mcp_altitude_valid)
-        printf("  MCP selected altitude:   %u ft\n", mm->nav.mcp_altitude);
+        printf("  MCP selected altitude:   %d ft\n", mm->nav.mcp_altitude);
     if (mm->nav.qnh_valid)
         printf("  QNH:                     %.1f millibars\n", mm->nav.qnh);
     if (mm->nav.altitude_source != NAV_ALT_INVALID) {

net_io.c

@@ -2706,8 +2706,8 @@ static void writeFATSV()
             (trackDataValid(&a->mach_valid) && fabs(a->mach - a->fatsv_emitted_mach) >= 0.02);
 
         int immediate =
-            (trackDataValid(&a->nav_altitude_mcp_valid) && unsigned_difference(a->nav_altitude_mcp, a->fatsv_emitted_nav_altitude_mcp) > 50) ||
-            (trackDataValid(&a->nav_altitude_fms_valid) && unsigned_difference(a->nav_altitude_fms, a->fatsv_emitted_nav_altitude_fms) > 50) ||
+            (trackDataValid(&a->nav_altitude_mcp_valid) && abs(a->nav_altitude_mcp - a->fatsv_emitted_nav_altitude_mcp) > 50) ||
+            (trackDataValid(&a->nav_altitude_fms_valid) && abs(a->nav_altitude_fms - a->fatsv_emitted_nav_altitude_fms) > 50) ||
             (trackDataValid(&a->nav_altitude_src_valid) && a->nav_altitude_src != a->fatsv_emitted_nav_altitude_src) ||
             (trackDataValid(&a->nav_heading_valid) && heading_difference(a->nav_heading, a->fatsv_emitted_nav_heading) > 2) ||
             (trackDataValid(&a->nav_modes_valid) && a->nav_modes != a->fatsv_emitted_nav_modes) ||
@@ -2821,8 +2821,8 @@ static void writeFATSV()
         p = appendFATSVMeta(p, end, "roll",        a, &a->roll_valid,           "%.1f", a->roll);
         p = appendFATSVMeta(p, end, "heading_magnetic", a, &a->mag_heading_valid, "%.1f", a->mag_heading);
         p = appendFATSVMeta(p, end, "heading_true", a, &a->true_heading_valid,    "%.1f", a->true_heading);
-        p = appendFATSVMeta(p, end, "nav_alt_mcp", a, &a->nav_altitude_mcp_valid, "%u",   a->nav_altitude_mcp);
-        p = appendFATSVMeta(p, end, "nav_alt_fms", a, &a->nav_altitude_fms_valid, "%u",   a->nav_altitude_fms);
+        p = appendFATSVMeta(p, end, "nav_alt_mcp", a, &a->nav_altitude_mcp_valid, "%d",   a->nav_altitude_mcp);
+        p = appendFATSVMeta(p, end, "nav_alt_fms", a, &a->nav_altitude_fms_valid, "%d",   a->nav_altitude_fms);
         p = appendFATSVMeta(p, end, "nav_alt_src", a, &a->nav_altitude_src_valid, "%s", nav_altitude_source_enum_string(a->nav_altitude_src));
         p = appendFATSVMeta(p, end, "nav_heading", a, &a->nav_heading_valid,    "%.1f", a->nav_heading);
         p = appendFATSVMeta(p, end, "nav_modes",   a, &a->nav_modes_valid,      "{%s}", nav_modes_flags_string(a->nav_modes));

track.h

@@ -167,10 +167,10 @@ struct aircraft {
     float         nav_qnh;        // Altimeter setting (QNH/QFE), millibars
 
     data_validity nav_altitude_mcp_valid;
-    unsigned      nav_altitude_mcp;    // FCU/MCP selected altitude
+    int           nav_altitude_mcp;    // FCU/MCP selected altitude
 
     data_validity nav_altitude_fms_valid;
-    unsigned      nav_altitude_fms;    // FMS selected altitude
+    int           nav_altitude_fms;    // FMS selected altitude
 
     data_validity nav_altitude_src_valid;
     nav_altitude_source_t nav_altitude_src;  // source of altitude used by automation
@@ -259,8 +259,8 @@ struct aircraft {
     unsigned      fatsv_emitted_tas;              //      -"-         TAS
     float         fatsv_emitted_mach;             //      -"-         Mach number
     airground_t   fatsv_emitted_airground;        //      -"-         air/ground state
-    unsigned      fatsv_emitted_nav_altitude_mcp; //      -"-         MCP altitude
-    unsigned      fatsv_emitted_nav_altitude_fms; //      -"-         FMS altitude
+    int           fatsv_emitted_nav_altitude_mcp; //      -"-         MCP altitude
+    int           fatsv_emitted_nav_altitude_fms; //      -"-         FMS altitude
     nav_altitude_source_t fatsv_emitted_nav_altitude_src; // -"-      automation altitude source
     float         fatsv_emitted_nav_heading;      //      -"-         target heading
     nav_modes_t   fatsv_emitted_nav_modes;        //      -"-         enabled navigation modes