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annotate libgsmfrp/comfort_noise.c @ 45:4ae1dd43e332

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libgsmefr/frame2params.c: brown paper bag
author Mychaela Falconia <falcon@freecalypso.org>
date Fri, 25 Nov 2022 02:40:21 +0000
parents 286d5f097eb4
children 3b64f255689a
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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 /* pseudonoise() function is based on ETSI EFR code */
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21
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22 static uint16_t pseudonoise(struct gsmfr_preproc_state *st, uint16_t no_bits)
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23 {
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24 uint16_t noise_bits, Sn, i;
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25
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26 noise_bits = 0;
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27 for (i = 0; i < no_bits; i++)
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28 {
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29 /* State n == 31 */
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30 if ((st->cn_random_lfsr & 0x00000001L) != 0)
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31 {
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32 Sn = 1;
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33 }
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34 else
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35 {
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36 Sn = 0;
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37 }
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38
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39 /* State n == 3 */
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40 if ((st->cn_random_lfsr & 0x10000000L) != 0)
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41 {
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42 Sn = Sn ^ 1;
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43 }
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44 else
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45 {
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46 Sn = Sn ^ 0;
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47 }
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48
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49 noise_bits = noise_bits << 1;
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50 noise_bits = noise_bits | st->cn_random_lfsr & 1;
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51
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52 st->cn_random_lfsr >>= 1;
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53 if (Sn & 1)
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54 {
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55 st->cn_random_lfsr |= 0x40000000L;
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56 }
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57 }
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58
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59 return noise_bits;
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60 }
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61
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62 static uint8_t random_1to6(struct gsmfr_preproc_state *st)
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63 {
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64 uint8_t range8, range6;
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65
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66 range8 = pseudonoise(st, 3);
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67 range6 = fold_table_8to6[(st->cn_random_6fold << 3) | range8];
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68 st->cn_random_6fold++;
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69 if (st->cn_random_6fold >= 3)
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70 st->cn_random_6fold = 0;
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71 return range6;
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72 }
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73
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74 void gsmfr_preproc_gen_cn(struct gsmfr_preproc_state *st, gsm_byte *frame)
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75 {
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76 unsigned sub, pulse;
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77 uint8_t Mc, xmc[13];
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78 gsm_byte *c;
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79
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80 /* global bytes (magic and LARc) are fixed */
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81 memcpy(frame, st->sid_prefix, 5);
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82 c = frame + 5;
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83 /* now do the 4 subframes, mostly PRNG output */
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84 for (sub = 0; sub < 4; sub++) {
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85 Mc = pseudonoise(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 /* packing code from libgsm */
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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++ = ((bc[sub] & 0x1) << 7)
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92 | ((Mc & 0x3) << 5)
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93 | ((st->sid_xmaxc[sub] >> 1) & 0x1F);
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94 *c++ = ((st->sid_xmaxc[sub] & 0x1) << 7)
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95 | ((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 }