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annotate libgsmfrp/sidclass.c @ 108:3b64f255689a

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libgsmfrp: factor out PRNG into its own module, in preparation for using it as part of speech muting too
author Mychaela Falconia <falcon@freecalypso.org>
date Mon, 28 Nov 2022 04:00:18 +0000
parents 2b5770c715ee
children
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1 /*
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2 * gsmfr_preproc_sid_classify() utility function classifies
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3 * a GSM 06.10 frame in RTP encoding according to the rules
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4 * of GSM 06.31 (or 3GPP TS 46.031) section 6.1.1, judging it
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5 * as SID=0, SID=1 or SID=2.
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6 */
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7
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8 #include "gsm_fr_preproc.h"
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9
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10 static const unsigned short sid_field_bits[95] = {
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11 57, 58, 60, 61, 63, 64, 66, 67, 69, 70, 72, 73,
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12 75, 76, 78, 79, 81, 82, 84, 85, 87, 88, 90, 91,
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13 93, 94, 113, 114, 116, 117, 119, 120, 122, 123,
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14 125, 126, 128, 129, 131, 132, 134, 135, 137,
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16 169, 170, 172, 173, 175, 176, 178, 179, 181,
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17 182, 184, 185, 187, 188, 190, 191, 193, 194,
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18 196, 197, 199, 200, 202, 203, 205, 206, 225,
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20 243, 246, 249, 252, 255, 258, 261
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21 };
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22
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23 static inline int get_bit(const gsm_byte *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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28
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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 gsmfr_preproc_sid_classify(const gsm_byte *frame)
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36 {
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37 unsigned idx, n;
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38
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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_field_bits[idx]))
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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 }