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annotate libgsmefr/lsp_az.c @ 485:751f06541fbb

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doc/Codec-utils: clarify lack of DHF in gsmfr-decode-rb
author Mychaela Falconia <falcon@freecalypso.org>
date Mon, 20 May 2024 01:47:22 +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 }