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annotate libgsmefr/sid_class.c @ 494:aaf4dec8bee0

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libgsmhr1: implement perfect SID detection
author Mychaela Falconia <falcon@freecalypso.org>
date Mon, 17 Jun 2024 23:14:19 +0000
parents b5726d659915
children
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1 /*
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2 * EFR_sid_classify() utility function classifies an EFR frame
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3 * in RTP encoding according to the rules of GSM 06.81 section 6.1.1,
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4 * judging it as SID=0, SID=1 or SID=2.
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5 */
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6
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7 #include "gsm_efr.h"
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8
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9 static const uint8_t SID_codeword_bit_idx[95] =
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10 {
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21 };
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23 static inline int get_bit(const uint8_t *frame, unsigned bitnum)
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24 {
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25 unsigned bytenum = bitnum >> 3;
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26 unsigned bit_in_byte = 7 - (bitnum & 7);
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27 unsigned bitmask = 1 << bit_in_byte;
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29 if (frame[bytenum] & bitmask)
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30 return 1;
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31 else
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32 return 0;
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33 }
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34
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35 int EFR_sid_classify(const uint8_t *frame)
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36 {
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37 unsigned idx, n;
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39 n = 0;
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40 for (idx = 0; idx < 95; idx++) {
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41 if (!get_bit(frame, SID_codeword_bit_idx[idx] + 4))
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42 n++;
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43 if (n >= 16)
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44 return 0;
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45 }
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46 if (n < 2)
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47 return 2;
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48 else
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49 return 1;
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50 }