diff --git a/dump1090.c b/dump1090.c index 4955410..e70efbd 100644 --- a/dump1090.c +++ b/dump1090.c @@ -1296,15 +1296,14 @@ int detectOutOfPhase(uint16_t *pPreamble) { * it will be more likely to detect a one because of the transformation. * In this way similar levels will be interpreted more likely in the * correct way. */ -void applyPhaseCorrection(uint16_t *m) { +void applyPhaseCorrection(uint16_t *pPayload) { int j; - for (j = 0; j < MODES_LONG_MSG_SAMPLES; j += 2) { - if (m[j] > m[j+1]) { - /* One */ - m[j+2] = (m[j+2] * 5) / 4; - } else { - /* Zero */ - m[j+2] = (m[j+2] * 4) / 5; + + for (j = 0; j < MODES_LONG_MSG_SAMPLES; j += 2, pPayload += 2) { + if (pPayload[0] > pPayload[1]) { /* One */ + pPayload[2] = (pPayload[2] * 5) / 4; + } else { /* Zero */ + pPayload[2] = (pPayload[2] * 4) / 5; } } } @@ -1345,10 +1344,12 @@ void detectModeS(uint16_t *m, uint32_t mlen) { for (j = 0; j < mlen; j++) { int low, high, delta, i, errors; int good_message = 0; - uint16_t *pPreamble; + uint16_t *pPreamble, *pPayload, *pPtr; int msglen; pPreamble = &m[j]; + pPayload = &m[j+MODES_PREAMBLE_SAMPLES]; + if (use_correction) goto good_preamble; /* We already checked it. */ /* First check of relations between the first 10 samples @@ -1404,42 +1405,39 @@ good_preamble: /* If the previous attempt with this message failed, retry using * magnitude correction. */ if (use_correction) { - memcpy(aux,m+j+MODES_PREAMBLE_SAMPLES,sizeof(aux)); - applyPhaseCorrection(m+j+MODES_PREAMBLE_SAMPLES); + memcpy(aux, pPayload, sizeof(aux)); + applyPhaseCorrection(aux); Modes.stat_out_of_phase++; - + pPayload = aux; /* TODO ... apply other kind of corrections. */ } /* Decode all the next 112 bits, regardless of the actual message * size. We'll check the actual message type later. */ + pPtr = pPayload; errors = 0; - for (i = 0; i < MODES_LONG_MSG_SAMPLES; i += 2) { - low = m[j+i+MODES_PREAMBLE_SAMPLES]; - high = m[j+i+MODES_PREAMBLE_SAMPLES+1]; + for (i = 0; i < MODES_LONG_MSG_BITS; i++) { + low = *pPtr++; + high = *pPtr++; delta = low-high; if (delta < 0) delta = -delta; if (i > 0 && delta < 256) { - bits[i/2] = bits[i/2-1]; + bits[i] = bits[i-1]; } else if (low == high) { /* Checking if two adiacent samples have the same magnitude * is an effective way to detect if it's just random noise * that was detected as a valid preamble. */ - bits[i/2] = 2; /* error */ + bits[i] = 2; /* error */ if (i < MODES_SHORT_MSG_SAMPLES) errors++; } else if (low > high) { - bits[i/2] = 1; + bits[i] = 1; } else { /* (low < high) for exclusion */ - bits[i/2] = 0; + bits[i] = 0; } } - /* Restore the original message if we used magnitude correction. */ - if (use_correction) - memcpy(m+j+MODES_PREAMBLE_SAMPLES,aux,sizeof(aux)); - /* Pack bits into bytes */ for (i = 0; i < MODES_LONG_MSG_BITS; i += 8) { msg[i/8] = @@ -1458,9 +1456,9 @@ good_preamble: /* Last check, high and low bits are different enough in magnitude * to mark this as real message and not just noise? */ delta = 0; - for (i = 0; i < msglen*8*2; i += 2) { - delta += abs(m[j+i+MODES_PREAMBLE_SAMPLES]- - m[j+i+MODES_PREAMBLE_SAMPLES+1]); + pPtr = pPayload; + for (i = 0; i < msglen*8; i ++, pPtr += 2) { + delta += abs(pPtr[0] - pPtr[1]); } delta /= msglen*4;