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Simplify ident decoding, add some sanity checks to the BDS2,0 case.

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This commit is contained in:
Oliver Jowett 2016-09-14 15:58:29 +01:00
parent 8e8b8588bf
commit b827806ce8
1 changed files with 28 additions and 37 deletions
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65
mode_s.c
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@ -736,30 +736,29 @@ int decodeModesMessage(struct modesMessage *mm, unsigned char *msg)
// Decode BDS2,0 carried in Comm-B or ES
static void decodeBDS20(struct modesMessage *mm)
{
uint32_t chars1, chars2;
unsigned char *msg = mm->msg;
chars1 = getbits(msg, 41, 64);
chars2 = getbits(msg, 65, 88);
// A common failure mode seems to be to intermittently send
// all zeros. Catch that here.
if (chars1 == 0 && chars2 == 0)
return;
mm->callsign[0] = ais_charset[getbits(msg, 41, 46)];
mm->callsign[1] = ais_charset[getbits(msg, 47, 52)];
mm->callsign[2] = ais_charset[getbits(msg, 53, 58)];
mm->callsign[3] = ais_charset[getbits(msg, 59, 64)];
mm->callsign[4] = ais_charset[getbits(msg, 65, 70)];
mm->callsign[5] = ais_charset[getbits(msg, 71, 76)];
mm->callsign[6] = ais_charset[getbits(msg, 77, 82)];
mm->callsign[7] = ais_charset[getbits(msg, 83, 88)];
mm->callsign[8] = 0;
// Catch possible bad decodings since BDS2,0 is not
// 100% reliable: accept only alphanumeric data
mm->callsign_valid = 1;
mm->callsign[3] = ais_charset[chars1 & 0x3F]; chars1 = chars1 >> 6;
mm->callsign[2] = ais_charset[chars1 & 0x3F]; chars1 = chars1 >> 6;
mm->callsign[1] = ais_charset[chars1 & 0x3F]; chars1 = chars1 >> 6;
mm->callsign[0] = ais_charset[chars1 & 0x3F];
mm->callsign[7] = ais_charset[chars2 & 0x3F]; chars2 = chars2 >> 6;
mm->callsign[6] = ais_charset[chars2 & 0x3F]; chars2 = chars2 >> 6;
mm->callsign[5] = ais_charset[chars2 & 0x3F]; chars2 = chars2 >> 6;
mm->callsign[4] = ais_charset[chars2 & 0x3F];
mm->callsign[8] = '\0';
for (int i = 0; i < 8; ++i) {
if (! ((mm->callsign[i] >= 'A' && mm->callsign[i] <= 'Z') ||
(mm->callsign[i] >= '0' && mm->callsign[i] <= '9') ||
mm->callsign[i] == ' ') ) {
mm->callsign_valid = 0;
break;
}
}
}
static void decodeESIdentAndCategory(struct modesMessage *mm)
@ -769,26 +768,18 @@ static void decodeESIdentAndCategory(struct modesMessage *mm)
mm->mesub = getbits(me, 6, 8);
unsigned chars1 = getbits(me, 9, 32);
unsigned chars2 = getbits(me, 33, 56);
mm->callsign[0] = ais_charset[getbits(me, 9, 14)];
mm->callsign[1] = ais_charset[getbits(me, 15, 20)];
mm->callsign[2] = ais_charset[getbits(me, 21, 26)];
mm->callsign[3] = ais_charset[getbits(me, 27, 32)];
mm->callsign[4] = ais_charset[getbits(me, 33, 38)];
mm->callsign[5] = ais_charset[getbits(me, 39, 44)];
mm->callsign[6] = ais_charset[getbits(me, 45, 50)];
mm->callsign[7] = ais_charset[getbits(me, 51, 56)];
// A common failure mode seems to be to intermittently send
// all zeros. Catch that here.
if (chars1 != 0 || chars2 != 0) {
mm->callsign_valid = 1;
mm->callsign[3] = ais_charset[chars1 & 0x3F]; chars1 = chars1 >> 6;
mm->callsign[2] = ais_charset[chars1 & 0x3F]; chars1 = chars1 >> 6;
mm->callsign[1] = ais_charset[chars1 & 0x3F]; chars1 = chars1 >> 6;
mm->callsign[0] = ais_charset[chars1 & 0x3F];
mm->callsign[7] = ais_charset[chars2 & 0x3F]; chars2 = chars2 >> 6;
mm->callsign[6] = ais_charset[chars2 & 0x3F]; chars2 = chars2 >> 6;
mm->callsign[5] = ais_charset[chars2 & 0x3F]; chars2 = chars2 >> 6;
mm->callsign[4] = ais_charset[chars2 & 0x3F];
mm->callsign[8] = '\0';
}
mm->callsign_valid = (strcmp(mm->callsign, "@@@@@@@@") != 0);
mm->category = ((0x0E - mm->metype) << 4) | mm->mesub;
mm->category_valid = 1;