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annotate libgsmefr/lsp_az.c @ 183:452c1d5a6268

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libgsmefr BFI w/o data: emit zero output after decoder reset In real-life usage, each EFR decoder session will most likely begin with lots of BFI frames before the first real frame arrives. However, because the spec-defined home state of the decoder is speech rather than CN, our regular logic for BFI w/o data would have to feed pseudorandom noise to the decoder (in the "fixed codebook excitation pulses" part), which is silly to do at the beginning of the decoder session right out of reset. Therefore, let's check reset_flag_old, and if we are still in the reset state, simply emit zero output.
author Mychaela Falconia <falcon@freecalypso.org>
date Tue, 03 Jan 2023 00:12:18 +0000
parents 5bc228bb421e
children
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1 /*************************************************************************
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2 *
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3 * FUNCTION: Lsp_Az
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4 *
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5 * PURPOSE: Converts from the line spectral pairs (LSP) to
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6 * LP coefficients, for a 10th order filter.
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7 *
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8 * DESCRIPTION:
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9 * - Find the coefficients of F1(z) and F2(z) (see Get_lsp_pol)
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10 * - Multiply F1(z) by 1+z^{-1} and F2(z) by 1-z^{-1}
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11 * - A(z) = ( F1(z) + F2(z) ) / 2
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12 *
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13 *************************************************************************/
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14
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15 #include "gsm_efr.h"
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16 #include "typedef.h"
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17 #include "namespace.h"
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18 #include "basic_op.h"
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19 #include "oper_32b.h"
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20 #include "no_count.h"
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21 #include "sig_proc.h"
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22
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23 /* local function */
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24
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25 static void Get_lsp_pol (Word16 *lsp, Word32 *f);
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26
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27 void Lsp_Az (
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28 Word16 lsp[], /* (i) : line spectral frequencies */
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29 Word16 a[] /* (o) : predictor coefficients (order = 10) */
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30 )
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31 {
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32 Word16 i, j;
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33 Word32 f1[6], f2[6];
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34 Word32 t0;
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35
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36 Get_lsp_pol (&lsp[0], f1);
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37 Get_lsp_pol (&lsp[1], f2);
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38
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39 for (i = 5; i > 0; i--)
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40 {
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41 f1[i] = L_add (f1[i], f1[i - 1]); move32 (); /* f1[i] += f1[i-1]; */
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42 f2[i] = L_sub (f2[i], f2[i - 1]); move32 (); /* f2[i] -= f2[i-1]; */
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43 }
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45 a[0] = 4096; move16 ();
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46 for (i = 1, j = 10; i <= 5; i++, j--)
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47 {
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48 t0 = L_add (f1[i], f2[i]); /* f1[i] + f2[i] */
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49 a[i] = extract_l (L_shr_r (t0, 13)); move16 ();
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50 t0 = L_sub (f1[i], f2[i]); /* f1[i] - f2[i] */
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51 a[j] = extract_l (L_shr_r (t0, 13)); move16 ();
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52 }
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53
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54 return;
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55 }
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56
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57 /*************************************************************************
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58 *
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59 * FUNCTION: Get_lsp_pol
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60 *
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61 * PURPOSE: Find the polynomial F1(z) or F2(z) from the LSPs.
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62 * If the LSP vector is passed at address 0 F1(z) is computed
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63 * and if it is passed at address 1 F2(z) is computed.
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64 *
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65 * DESCRIPTION:
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66 * This is performed by expanding the product polynomials:
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67 *
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68 * F1(z) = product ( 1 - 2 lsp[i] z^-1 + z^-2 )
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69 * i=0,2,4,6,8
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70 * F2(z) = product ( 1 - 2 lsp[i] z^-1 + z^-2 )
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71 * i=1,3,5,7,9
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72 *
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73 * where lsp[] is the LSP vector in the cosine domain.
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74 *
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75 * The expansion is performed using the following recursion:
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76 *
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77 * f[0] = 1
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78 * b = -2.0 * lsp[0]
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79 * f[1] = b
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80 * for i=2 to 5 do
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81 * b = -2.0 * lsp[2*i-2];
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82 * f[i] = b*f[i-1] + 2.0*f[i-2];
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83 * for j=i-1 down to 2 do
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84 * f[j] = f[j] + b*f[j-1] + f[j-2];
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85 * f[1] = f[1] + b;
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86 *
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87 *************************************************************************/
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88
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89 static void Get_lsp_pol (Word16 *lsp, Word32 *f)
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90 {
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91 Word16 i, j, hi, lo;
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92 Word32 t0;
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93
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94 /* f[0] = 1.0; */
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95 *f = L_mult (4096, 2048); move32 ();
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96 f++; move32 ();
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97 *f = L_msu ((Word32) 0, *lsp, 512); /* f[1] = -2.0 * lsp[0]; */
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98 f++; move32 ();
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99 lsp += 2; /* Advance lsp pointer */
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100
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101 for (i = 2; i <= 5; i++)
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102 {
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103 *f = f[-2]; move32 ();
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104
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105 for (j = 1; j < i; j++, f--)
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106 {
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107 L_Extract (f[-1], &hi, &lo);
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108 t0 = Mpy_32_16 (hi, lo, *lsp); /* t0 = f[-1] * lsp */
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109 t0 = L_shl (t0, 1);
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110 *f = L_add (*f, f[-2]); move32 (); /* *f += f[-2] */
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111 *f = L_sub (*f, t0);move32 (); /* *f -= t0 */
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112 }
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113 *f = L_msu (*f, *lsp, 512); move32 (); /* *f -= lsp<<9 */
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114 f += i; /* Advance f pointer */
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115 lsp += 2; /* Advance lsp pointer */
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116 }
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117
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118 return;
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119 }