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Improve callsign extraction from DF17

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Use 32 bit registers to hold multiple characters and shift them. This
removes the need for multiple memory reads.

Also tidy up the DF-17 extraction routine to make it more readable.
This commit is contained in:
Malcolm Robb 2013-04-30 18:12:18 +01:00
parent 539faaaf27
commit 14c54599ac
1 changed files with 27 additions and 28 deletions
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55
dump1090.c
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@ -1477,31 +1477,31 @@ void decodeModesMessage(struct modesMessage *mm, unsigned char *msg) {
// Decode the extended squitter message
if (mm->metype >= 1 && mm->metype <= 4) {
/* Aircraft Identification and Category */
mm->aircraft_type = mm->metype-1;
mm->flight[0] = ais_charset[msg[5]>>2];
mm->flight[1] = ais_charset[((msg[5]&3)<<4)|(msg[6]>>4)];
mm->flight[2] = ais_charset[((msg[6]&15)<<2)|(msg[7]>>6)];
mm->flight[3] = ais_charset[msg[7]&63];
mm->flight[4] = ais_charset[msg[8]>>2];
mm->flight[5] = ais_charset[((msg[8]&3)<<4)|(msg[9]>>4)];
mm->flight[6] = ais_charset[((msg[9]&15)<<2)|(msg[10]>>6)];
mm->flight[7] = ais_charset[msg[10]&63];
if (mm->metype >= 1 && mm->metype <= 4) { // Aircraft Identification and Category
uint32_t chars;
chars = (msg[5] << 16) | (msg[6] << 8) | (msg[7]);
mm->flight[3] = ais_charset[chars & 0x3F]; chars = chars >> 6;
mm->flight[2] = ais_charset[chars & 0x3F]; chars = chars >> 6;
mm->flight[1] = ais_charset[chars & 0x3F]; chars = chars >> 6;
mm->flight[0] = ais_charset[chars & 0x3F];
chars = (msg[8] << 16) | (msg[9] << 8) | (msg[10]);
mm->flight[7] = ais_charset[chars & 0x3F]; chars = chars >> 6;
mm->flight[6] = ais_charset[chars & 0x3F]; chars = chars >> 6;
mm->flight[5] = ais_charset[chars & 0x3F]; chars = chars >> 6;
mm->flight[4] = ais_charset[chars & 0x3F];
mm->flight[8] = '\0';
} else if (mm->metype >= 9 && mm->metype <= 18) {
/* Airborne position Message */
} else if (mm->metype >= 9 && mm->metype <= 18) { // Airborne position Message
mm->fflag = msg[6] & (1<<2);
mm->tflag = msg[6] & (1<<3);
mm->altitude = decodeAC12Field(((msg[5] << 4) | (msg[6] >> 4)), &mm->unit);
mm->raw_latitude = ((msg[6] & 3) << 15) |
(msg[7] << 7) |
(msg[8] >> 1);
mm->raw_longitude = ((msg[8]&1) << 16) |
(msg[9] << 8) |
msg[10];
} else if (mm->metype == 19 && mm->mesub >= 1 && mm->mesub <= 4) {
/* Airborne Velocity Message */
mm->raw_latitude = ((msg[6] & 3) << 15) | (msg[7] << 7) | (msg[8] >> 1);
mm->raw_longitude = ((msg[8] & 1) << 16) | (msg[9] << 8) | (msg[10]);
} else if (mm->metype == 19) { // Airborne Velocity Message
if (mm->mesub == 1 || mm->mesub == 2) {
mm->ew_dir = (msg[5]&4) >> 2;
mm->ew_velocity = ((msg[5]&3) << 8) | msg[6];
@ -1510,9 +1510,8 @@ void decodeModesMessage(struct modesMessage *mm, unsigned char *msg) {
mm->vert_rate_source = (msg[8]&0x10) >> 4;
mm->vert_rate_sign = (msg[8]&0x8) >> 3;
mm->vert_rate = ((msg[8]&7) << 6) | ((msg[9]&0xfc) >> 2);
/* Compute velocity and angle from the two speed
* components. */
mm->velocity = (int) sqrt(mm->ns_velocity*mm->ns_velocity+
// Compute velocity and angle from the two speed components
mm->velocity = (int) sqrt(mm->ns_velocity*mm->ns_velocity +
mm->ew_velocity*mm->ew_velocity);
if (mm->velocity) {
int ewv = mm->ew_velocity;
@ -1523,17 +1522,17 @@ void decodeModesMessage(struct modesMessage *mm, unsigned char *msg) {
if (mm->ns_dir) nsv *= -1;
heading = atan2(ewv,nsv);
/* Convert to degrees. */
// Convert to degrees
mm->heading = (int) (heading * 360 / (M_PI*2));
/* We don't want negative values but a 0-360 scale. */
// We don't want negative values but a 0-360 scale
if (mm->heading < 0) mm->heading += 360;
} else {
mm->heading = 0;
}
} else if (mm->mesub == 3 || mm->mesub == 4) {
mm->heading_is_valid = msg[5] & (1<<2);
mm->heading = (int) (360.0/128) * (((msg[5] & 3) << 5) |
(msg[6] >> 3));
mm->heading = (int) (360.0/128) * (((msg[5] & 3) << 5) | (msg[6] >> 3));
}
}
}