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Table-ize the Mode A to C conversions, add a Mode C to Mode A conversion function.

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This commit is contained in:
Oliver Jowett 2016-10-11 17:57:25 +01:00
parent 10b5cde505
commit 60f1f3bcb6
7 changed files with 68 additions and 7 deletions
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52
mode_ac.c
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@ -29,15 +29,59 @@
//
#include "dump1090.h"
#include <assert.h>
//
//=========================================================================
//
// Input format is : 00:A4:A2:A1:00:B4:B2:B1:00:C4:C2:C1:00:D4:D2:D1
//
int ModeAToModeC(unsigned int ModeA)
static int modeAToCTable[4096];
static unsigned modeCToATable[4096];
static int internalModeAToModeC(unsigned int ModeA);
void modeACInit()
{
unsigned int FiveHundreds = 0;
unsigned int OneHundreds = 0;
for (unsigned i = 0; i < 4096; ++i) {
unsigned modeA = indexToModeA(i);
int modeC = internalModeAToModeC(modeA);
modeAToCTable[i] = modeC;
modeC += 13;
if (modeC >= 0 && modeC < 4096) {
assert(modeCToATable[modeC] == 0);
modeCToATable[modeC] = modeA;
}
}
}
// Given a mode A value (hex-encoded, see above)
// return the mode C value (signed multiple of 100s of feet)
// or INVALID_ALITITUDE if not a valid mode C value
int modeAToModeC(unsigned modeA)
{
unsigned i = modeAToIndex(modeA);
if (i >= 4096)
return INVALID_ALTITUDE;
return modeAToCTable[i];
}
// Given a mode C value (signed multiple of 100s of feet)
// return the mode A value, or 0 if not a valid mode C value
unsigned modeCToModeA(int modeC)
{
modeC += 13;
if (modeC < 0 || modeC >= 4096)
return 0;
return modeCToATable[modeC];
}
static int internalModeAToModeC(unsigned int ModeA)
{
unsigned int FiveHundreds = 0;
unsigned int OneHundreds = 0;
if ((ModeA & 0xFFFF8889) != 0 || // check zero bits are zero, D1 set is illegal
(ModeA & 0x000000F0) == 0) { // C1,,C4 cannot be Zero
@ -100,7 +144,7 @@ void decodeModeAMessage(struct modesMessage *mm, int ModeA)
// Decode an altitude if this looks like a possible mode C
if (!mm->spi) {
int modeC = ModeAToModeC(ModeA);
int modeC = modeAToModeC(ModeA);
if (modeC != INVALID_ALTITUDE) {
mm->altitude = modeC * 100;
mm->altitude_unit = UNIT_FEET;