NMT: Changes in parity check
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@ -879,6 +879,9 @@ static void encode_digits(const uint8_t *digits, char *bits)
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bits[(i << 1) + 1] = x[i - 6] + '0';
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}
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/* debug parity check */
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//#define DEBUG_DECODE
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/* decode digits from 140 bits (not including sync) */
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// FIXME: do real convolutional decoding
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static int decode_digits(uint8_t *digits, const char *bits, int callack)
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@ -888,8 +891,12 @@ static int decode_digits(uint8_t *digits, const char *bits, int callack)
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/* information bits */
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for (i = 0; i < 6; i++) {
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if (bits[(i << 1) + 1] != '0')
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if (bits[(i << 1) + 1] != '0') {
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#ifdef DEBUG_DECODE
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PDEBUG(DFRAME, DEBUG_DEBUG, "Frame bad at information bit #%d.\n", i);
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#endif
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return -1;
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}
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}
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for (i = 6; i < 70; i++)
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x[i - 6] = bits[(i << 1) + 1] - '0';
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@ -908,13 +915,22 @@ static int decode_digits(uint8_t *digits, const char *bits, int callack)
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digits[14] = 0;
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digits[15] = 0;
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short_frame = 1;
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#ifdef DEBUG_DECODE
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PDEBUG(DFRAME, DEBUG_DEBUG, "Received shortened frame\n");
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#endif
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}
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/* parity check bits */
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for (i = 0; i < 3; i++) {
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if (bits[(i << 1)] != '1' - x[i])
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if (bits[(i << 1)] != '1' - x[i]) {
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#ifdef DEBUG_DECODE
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PDEBUG(DFRAME, DEBUG_DEBUG, "Frame bad at parity bit #%d.\n", i);
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#endif
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return -1;
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}
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}
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#if 0
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#warning this check does not work, since we get error even at bit 50
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for (i = 3; i < ((short_frame) ? 52 : 64); i++) {
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if (bits[(i << 1)] != '1' - (x[i] ^ x[i - 3])) {
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/* According to NMT Doc 450-3, bits after Y(114) shall
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@ -930,18 +946,43 @@ static int decode_digits(uint8_t *digits, const char *bits, int callack)
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digits[13] = 0;
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break;
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}
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#ifdef DEBUG_DECODE
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PDEBUG(DFRAME, DEBUG_DEBUG, "Frame bad at parity bit #%d.\n", i);
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#endif
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return -1;
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}
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}
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#endif
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/* Tests showed corrupt frame at parity #50 (i == 50)
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* We just ignore whatever we receive after 48 bits of checksum.
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* This is not the correct approach, but in case of a corrupt
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* frame 10.a, we would drop it, if it failes later checks.
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*/
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for (i = 3; i < ((short_frame) ? 48 : 64); i++) {
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if (bits[(i << 1)] != '1' - (x[i] ^ x[i - 3])) {
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#ifdef DEBUG_DECODE
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PDEBUG(DFRAME, DEBUG_DEBUG, "Frame bad at parity bit #%d.\n", i);
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#endif
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return -1;
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}
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}
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if (short_frame)
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return 0;
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for (i = 64; i < 67; i++) {
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if (bits[(i << 1)] != '1' - x[i - 3])
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if (bits[(i << 1)] != '1' - x[i - 3]) {
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#ifdef DEBUG_DECODE
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PDEBUG(DFRAME, DEBUG_DEBUG, "Frame bad at parity bit #%d.\n", i);
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#endif
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return -1;
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}
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}
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for (i = 67; i < 70; i++) {
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if (bits[(i << 1)] != '1')
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if (bits[(i << 1)] != '1') {
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#ifdef DEBUG_DECODE
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PDEBUG(DFRAME, DEBUG_DEBUG, "Frame bad at parity bit #%d.\n", i);
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#endif
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return -1;
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}
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}
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return 0;
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