FreeCalypso > hg > gsm-codec-lib
annotate libgsmfrp/comfort_noise.c @ 95:f80a3202c8ff
libgsmefr: implement main decoder wrapper
author | Mychaela Falconia <falcon@freecalypso.org> |
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date | Sat, 26 Nov 2022 18:58:56 +0000 |
parents | 286d5f097eb4 |
children | 3b64f255689a |
rev | line source |
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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 } |