99 lines
3.1 KiB
C
99 lines
3.1 KiB
C
|
// Part of dump1090, a Mode S message decoder for RTLSDR devices.
|
||
|
|
//
|
||
|
|
// mode_s.h: Mode S message decoding (prototypes)
|
||
|
|
//
|
||
|
|
// Copyright (c) 2017 FlightAware, LLC
|
||
|
|
// Copyright (c) 2017 Oliver Jowett <oliver@mutability.co.uk>
|
||
|
|
//
|
||
|
|
// This file is free software: you may copy, redistribute and/or modify it
|
||
|
|
// under the terms of the GNU General Public License as published by the
|
||
|
|
// Free Software Foundation, either version 2 of the License, or (at your
|
||
|
|
// option) any later version.
|
||
|
|
//
|
||
|
|
// This file is distributed in the hope that it will be useful, but
|
||
|
|
// WITHOUT ANY WARRANTY; without even the implied warranty of
|
||
|
|
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
|
||
|
|
// General Public License for more details.
|
||
|
|
//
|
||
|
|
// You should have received a copy of the GNU General Public License
|
||
|
|
// along with this program. If not, see <http://www.gnu.org/licenses/>.
|
||
|
|
|
||
|
|
#ifndef MODE_S_H
|
||
|
|
#define MODE_S_H
|
||
|
|
|
||
|
|
#include <assert.h>
|
||
|
|
|
||
|
|
//
|
||
|
|
// Functions exported from mode_s.c
|
||
|
|
//
|
||
|
|
int modesMessageLenByType(int type);
|
||
|
|
int scoreModesMessage(unsigned char *msg, int validbits);
|
||
|
|
int decodeModesMessage (struct modesMessage *mm, unsigned char *msg);
|
||
|
|
void displayModesMessage(struct modesMessage *mm);
|
||
|
|
void useModesMessage (struct modesMessage *mm);
|
||
|
|
|
||
|
|
// datafield extraction helpers
|
||
|
|
|
||
|
|
// The first bit (MSB of the first byte) is numbered 1, for consistency
|
||
|
|
// with how the specs number them.
|
||
|
|
|
||
|
|
// Extract one bit from a message.
|
||
|
|
static inline __attribute__((always_inline)) unsigned getbit(unsigned char *data, unsigned bitnum)
|
||
|
|
{
|
||
|
|
unsigned bi = bitnum - 1;
|
||
|
|
unsigned by = bi >> 3;
|
||
|
|
unsigned mask = 1 << (7 - (bi & 7));
|
||
|
|
|
||
|
|
return (data[by] & mask) != 0;
|
||
|
|
}
|
||
|
|
|
||
|
|
// Extract some bits (firstbit .. lastbit inclusive) from a message.
|
||
|
|
static inline __attribute__((always_inline)) unsigned getbits(unsigned char *data, unsigned firstbit, unsigned lastbit)
|
||
|
|
{
|
||
|
|
unsigned fbi = firstbit - 1;
|
||
|
|
unsigned lbi = lastbit - 1;
|
||
|
|
unsigned nbi = (lastbit - firstbit + 1);
|
||
|
|
|
||
|
|
unsigned fby = fbi >> 3;
|
||
|
|
unsigned lby = lbi >> 3;
|
||
|
|
unsigned nby = (lby - fby) + 1;
|
||
|
|
|
||
|
|
unsigned shift = 7 - (lbi & 7);
|
||
|
|
unsigned topmask = 0xFF >> (fbi & 7);
|
||
|
|
|
||
|
|
assert (fbi <= lbi);
|
||
|
|
assert (nbi <= 32);
|
||
|
|
assert (nby <= 5);
|
||
|
|
|
||
|
|
if (nby == 5) {
|
||
|
|
return
|
||
|
|
((data[fby] & topmask) << (32 - shift)) |
|
||
|
|
(data[fby + 1] << (24 - shift)) |
|
||
|
|
(data[fby + 2] << (16 - shift)) |
|
||
|
|
(data[fby + 3] << (8 - shift)) |
|
||
|
|
(data[fby + 4] >> shift);
|
||
|
|
} else if (nby == 4) {
|
||
|
|
return
|
||
|
|
((data[fby] & topmask) << (24 - shift)) |
|
||
|
|
(data[fby + 1] << (16 - shift)) |
|
||
|
|
(data[fby + 2] << (8 - shift)) |
|
||
|
|
(data[fby + 3] >> shift);
|
||
|
|
} else if (nby == 3) {
|
||
|
|
return
|
||
|
|
((data[fby] & topmask) << (16 - shift)) |
|
||
|
|
(data[fby + 1] << (8 - shift)) |
|
||
|
|
(data[fby + 2] >> shift);
|
||
|
|
} else if (nby == 2) {
|
||
|
|
return
|
||
|
|
((data[fby] & topmask) << (8 - shift)) |
|
||
|
|
(data[fby + 1] >> shift);
|
||
|
|
} else if (nby == 1) {
|
||
|
|
return
|
||
|
|
(data[fby] & topmask) >> shift;
|
||
|
|
} else {
|
||
|
|
return 0;
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
#endif
|