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annotate libgsmfrp/comfort_noise.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 286d5f097eb4
children f081a6850fb5
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286d5f097eb4 libgsmfrp: implement comfort noise generation
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1 /*
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2 * In this module we implement comfort noise generation per GSM 06.12
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3 * or 3GPP TS 46.012.
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4 */
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5
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6 #include <stdint.h>
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7 #include <string.h>
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8 #include "gsm_fr_preproc.h"
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9 #include "internal.h"
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10
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11 static const uint8_t fold_table_8to6[24] = {
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12 1, 2, 3, 4, 5, 6, 1, 2,
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13 1, 2, 3, 4, 5, 6, 3, 4,
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14 1, 2, 3, 4, 5, 6, 5, 6,
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15 };
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16
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17 static const uint8_t bc[4] = {0, 0, 0, 0};
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18 static const uint8_t Nc[4] = {40, 120, 40, 120};
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19
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20 static uint8_t random_1to6(struct gsmfr_preproc_state *st)
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21 {
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22 uint8_t range8, range6;
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23
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24 range8 = gsmfr_preproc_prng(st, 3);
4
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25 range6 = fold_table_8to6[(st->cn_random_6fold << 3) | range8];
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26 st->cn_random_6fold++;
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27 if (st->cn_random_6fold >= 3)
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28 st->cn_random_6fold = 0;
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29 return range6;
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30 }
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31
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32 void gsmfr_preproc_gen_cn(struct gsmfr_preproc_state *st, gsm_byte *frame)
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33 {
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34 unsigned sub, pulse;
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35 uint8_t Mc, xmc[13];
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36 gsm_byte *c;
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37
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38 /* global bytes (magic and LARc) are fixed */
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39 memcpy(frame, st->sid_prefix, 5);
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40 c = frame + 5;
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41 /* now do the 4 subframes, mostly PRNG output */
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42 for (sub = 0; sub < 4; sub++) {
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43 Mc = gsmfr_preproc_prng(st, 2);
4
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44 for (pulse = 0; pulse < 13; pulse++)
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45 xmc[pulse] = random_1to6(st);
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46 /* packing code from libgsm */
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47 *c++ = ((Nc[sub] & 0x7F) << 1)
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48 | ((bc[sub] >> 1) & 0x1);
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49 *c++ = ((bc[sub] & 0x1) << 7)
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50 | ((Mc & 0x3) << 5)
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51 | ((st->sid_xmaxc[sub] >> 1) & 0x1F);
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52 *c++ = ((st->sid_xmaxc[sub] & 0x1) << 7)
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53 | ((xmc[0] & 0x7) << 4)
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54 | ((xmc[1] & 0x7) << 1)
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55 | ((xmc[2] >> 2) & 0x1);
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56 *c++ = ((xmc[2] & 0x3) << 6)
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57 | ((xmc[3] & 0x7) << 3)
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58 | (xmc[4] & 0x7);
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59 *c++ = ((xmc[5] & 0x7) << 5)
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60 | ((xmc[6] & 0x7) << 2)
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61 | ((xmc[7] >> 1) & 0x3);
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62 *c++ = ((xmc[7] & 0x1) << 7)
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63 | ((xmc[8] & 0x7) << 4)
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64 | ((xmc[9] & 0x7) << 1)
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65 | ((xmc[10] >> 2) & 0x1);
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66 *c++ = ((xmc[10] & 0x3) << 6)
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67 | ((xmc[11] & 0x7) << 3)
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68 | (xmc[12] & 0x7);
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69 }
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70 }