FreeCalypso > hg > gsm-codec-lib

annotate libgsmfr2/comfort_noise.c @ 478:936a08cc73ce

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doc/AMR-library-API: describe the decoder
author Mychaela Falconia <falcon@freecalypso.org>
date Sun, 19 May 2024 21:32:31 +0000
parents 573afa985df6
children
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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 "tw_gsmfr.h"
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9 #include "pp_state.h"
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10 #include "pp_internal.h"
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11
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12 static const uint8_t fold_table_8to6[24] = {
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13 1, 2, 3, 4, 5, 6, 1, 2,
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14 1, 2, 3, 4, 5, 6, 3, 4,
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15 1, 2, 3, 4, 5, 6, 5, 6,
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16 };
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17
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18 static const uint8_t bc[4] = {0, 0, 0, 0};
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19 static const uint8_t Nc[4] = {40, 120, 40, 120};
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20
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21 static uint8_t random_1to6(struct gsmfr_preproc_state *st)
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22 {
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23 uint8_t range8, range6;
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24
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25 range8 = gsmfr_preproc_prng(st, 3);
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26 range6 = fold_table_8to6[(st->cn_random_6fold << 3) | range8];
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27 st->cn_random_6fold++;
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28 if (st->cn_random_6fold >= 3)
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29 st->cn_random_6fold = 0;
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30 return range6;
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31 }
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32
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33 void gsmfr_preproc_gen_cn(struct gsmfr_preproc_state *st, uint8_t *frame)
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34 {
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35 unsigned sub, pulse;
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36 uint8_t Mc, xmc[13];
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37 uint8_t *c;
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38
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39 /* global bytes (magic and LARc) are fixed */
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40 memcpy(frame, st->sid_prefix, 5);
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41 c = frame + 5;
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42 /* now do the 4 subframes, mostly PRNG output */
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43 for (sub = 0; sub < 4; sub++) {
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44 Mc = gsmfr_preproc_prng(st, 2);
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45 for (pulse = 0; pulse < 13; pulse++)
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46 xmc[pulse] = random_1to6(st);
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47 /* packing code from libgsm */
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48 *c++ = ((Nc[sub] & 0x7F) << 1)
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49 | ((bc[sub] >> 1) & 0x1);
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50 *c++ = ((bc[sub] & 0x1) << 7)
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51 | ((Mc & 0x3) << 5)
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52 | ((st->sid_xmaxc >> 1) & 0x1F);
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53 *c++ = ((st->sid_xmaxc & 0x1) << 7)
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54 | ((xmc[0] & 0x7) << 4)
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55 | ((xmc[1] & 0x7) << 1)
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56 | ((xmc[2] >> 2) & 0x1);
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57 *c++ = ((xmc[2] & 0x3) << 6)
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58 | ((xmc[3] & 0x7) << 3)
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59 | (xmc[4] & 0x7);
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60 *c++ = ((xmc[5] & 0x7) << 5)
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61 | ((xmc[6] & 0x7) << 2)
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62 | ((xmc[7] >> 1) & 0x3);
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63 *c++ = ((xmc[7] & 0x1) << 7)
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64 | ((xmc[8] & 0x7) << 4)
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65 | ((xmc[9] & 0x7) << 1)
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66 | ((xmc[10] >> 2) & 0x1);
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67 *c++ = ((xmc[10] & 0x3) << 6)
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68 | ((xmc[11] & 0x7) << 3)
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69 | (xmc[12] & 0x7);
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70 }
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71 }
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72
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73 void gsmfr_preproc_sid2cn(struct gsmfr_preproc_state *st, uint8_t *frame)
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74 {
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75 unsigned sub, pulse;
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76 uint8_t Mc, xmc[13];
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77 uint8_t *c;
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78
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79 /* save LARc and Xmaxc from the last subframe for subsequent CN gen */
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80 memcpy(st->sid_prefix, frame, 5);
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81 st->sid_xmaxc = ((frame[27] & 0x1F) << 1) | (frame[28] >> 7);
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82 /* ... and turn *this* frame into very first CN output */
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83 c = frame + 5;
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84 for (sub = 0; sub < 4; sub++) {
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85 Mc = gsmfr_preproc_prng(st, 2);
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86 for (pulse = 0; pulse < 13; pulse++)
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87 xmc[pulse] = random_1to6(st);
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88 /* keep each of Xmaxc and replace the rest with CN */
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89 *c++ = ((Nc[sub] & 0x7F) << 1)
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90 | ((bc[sub] >> 1) & 0x1);
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91 *c &= 0x1F;
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92 *c++ |= ((bc[sub] & 0x1) << 7)
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93 | ((Mc & 0x3) << 5);
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94 *c &= 0x80;
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95 *c++ |= ((xmc[0] & 0x7) << 4)
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96 | ((xmc[1] & 0x7) << 1)
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97 | ((xmc[2] >> 2) & 0x1);
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98 *c++ = ((xmc[2] & 0x3) << 6)
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99 | ((xmc[3] & 0x7) << 3)
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100 | (xmc[4] & 0x7);
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101 *c++ = ((xmc[5] & 0x7) << 5)
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102 | ((xmc[6] & 0x7) << 2)
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103 | ((xmc[7] >> 1) & 0x3);
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104 *c++ = ((xmc[7] & 0x1) << 7)
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105 | ((xmc[8] & 0x7) << 4)
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106 | ((xmc[9] & 0x7) << 1)
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107 | ((xmc[10] >> 2) & 0x1);
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108 *c++ = ((xmc[10] & 0x3) << 6)
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109 | ((xmc[11] & 0x7) << 3)
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110 | (xmc[12] & 0x7);
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111 }
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112 }