adsb-tools/adsbus/packet.c

#pragma GCC diagnostic ignored "-Wtautological-constant-out-of-range-compare"

#include <assert.h>
#include <string.h>

#include "uuid.h"

#include "packet.h"

char *packet_type_names[] = {
	"INVALID",
	"Mode-AC",
	"Mode-S short",
	"Mode-S long",
};

size_t packet_payload_len[] = {
	0,
	2,
	7,
	14,
};

static uint64_t packet_mlat_timestamp_scale_mhz_in(uint64_t timestamp, uint32_t mhz) {
	assert(mhz > 0);
	return timestamp * (PACKET_MLAT_MHZ / mhz);
}

static uint64_t packet_mlat_timestamp_scale_width_in(uint64_t timestamp, uint64_t max, struct packet_mlat_state *state) {
	if (timestamp < state->timestamp_last) {
		// Counter reset
		state->timestamp_generation += max;
	}

	state->timestamp_last = timestamp;
	return state->timestamp_generation + timestamp;
}

static uint64_t packet_mlat_timestamp_scale_mhz_out(uint64_t timestamp, uint64_t mhz) {
	assert(mhz > 0);
	return timestamp / (PACKET_MLAT_MHZ / mhz);
}

static uint64_t packet_mlat_timestamp_scale_width_out(uint64_t timestamp, uint64_t max) {
	assert(max > 0);
	return timestamp % max;
}

uint64_t packet_mlat_timestamp_scale_in(uint64_t timestamp, uint64_t max, uint16_t mhz, struct packet_mlat_state *state) {
	return packet_mlat_timestamp_scale_mhz_in(packet_mlat_timestamp_scale_width_in(timestamp, max, state), mhz) % PACKET_MLAT_MAX;
}

uint64_t packet_mlat_timestamp_scale_out(uint64_t timestamp, uint64_t max, uint16_t mhz) {
	return packet_mlat_timestamp_scale_width_out(packet_mlat_timestamp_scale_mhz_out(timestamp, mhz), max);
}

uint32_t packet_rssi_scale_in(uint32_t value, uint32_t max) {
	assert(max > 0);
	return value * (PACKET_RSSI_MAX / max);
}

uint32_t packet_rssi_scale_out(uint32_t value, uint32_t max) {
	assert(max > 0);
	return value / (PACKET_RSSI_MAX / max);
}

void packet_sanity_check(const struct packet *packet) {
	assert(packet_validate_id(packet->source_id));
	assert(packet->type > PACKET_TYPE_NONE && packet->type < NUM_TYPES);
	assert(packet->mlat_timestamp <= PACKET_MLAT_MAX);
	assert(packet->rssi <= PACKET_RSSI_MAX);
}

bool packet_validate_id(const uint8_t *id) {
	if (!id) {
		return false;
	}
	for (size_t i = 0; i < UUID_LEN; i++) {
		uint8_t c = id[i];
		if (c == 0) {
			return true;
		}
		if (c < 32 || c > 126) {
			return false;
		}
	}
	return false;
}