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annotate libgsmfr2/preprocess.c @ 536:a3300483ae74

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doc/FR1-library-API: document return value from gsmfr_tfo_xfrm_*
author Mychaela Falconia <falcon@freecalypso.org>
date Sat, 21 Sep 2024 20:48:58 +0000
parents bd2271cb95d4
children
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1 /*
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2 * This C source file has been adapted from TU-Berlin libgsm source,
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3 * original notice follows:
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4 *
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5 * Copyright 1992 by Jutta Degener and Carsten Bormann, Technische
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6 * Universitaet Berlin. See the accompanying file "COPYRIGHT" for
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7 * details. THERE IS ABSOLUTELY NO WARRANTY FOR THIS SOFTWARE.
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8 */
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9
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10 #include <stdint.h>
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11 #include <assert.h>
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12 #include "tw_gsmfr.h"
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13 #include "typedef.h"
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14 #include "ed_state.h"
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15 #include "ed_internal.h"
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16
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17 /* 4.2.0 .. 4.2.3 PREPROCESSING SECTION
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18 *
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19 * After A-law to linear conversion (or directly from the
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20 * Ato D converter) the following scaling is assumed for
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21 * input to the RPE-LTP algorithm:
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22 *
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23 * in: 0.1.....................12
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24 * S.v.v.v.v.v.v.v.v.v.v.v.v.*.*.*
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25 *
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26 * Where S is the sign bit, v a valid bit, and * a "don't care" bit.
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27 * The original signal is called sop[..]
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28 *
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29 * out: 0.1................... 12
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30 * S.S.v.v.v.v.v.v.v.v.v.v.v.v.0.0
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31 */
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32
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33 void Gsm_Preprocess (
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34 struct gsmfr_0610_state * S,
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35 const word * s,
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36 word * so ) /* [0..159] IN/OUT */
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37 {
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38
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39 word z1 = S->z1;
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40 longword L_z2 = S->L_z2;
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41 word mp = S->mp;
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42
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43 word s1;
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44 longword L_s2;
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45
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46 longword L_temp;
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47
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48 word msp, lsp;
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49 word SO;
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50
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51 longword ltmp; /* for ADD */
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52 ulongword utmp; /* for L_ADD */
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53
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54 register int k = 160;
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55
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56 while (k--) {
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57
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58 /* 4.2.1 Downscaling of the input signal
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59 */
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60 SO = SASR( *s, 3 ) << 2;
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61 s++;
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62
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63 assert (SO >= -0x4000); /* downscaled by */
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64 assert (SO <= 0x3FFC); /* previous routine. */
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65
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66
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67 /* 4.2.2 Offset compensation
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68 *
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69 * This part implements a high-pass filter and requires extended
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70 * arithmetic precision for the recursive part of this filter.
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71 * The input of this procedure is the array so[0...159] and the
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72 * output the array sof[ 0...159 ].
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73 */
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74 /* Compute the non-recursive part
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75 */
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76
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77 s1 = SO - z1; /* s1 = gsm_sub( *so, z1 ); */
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78 z1 = SO;
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79
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80 assert(s1 != MIN_WORD);
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81
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82 /* Compute the recursive part
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83 */
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84 L_s2 = s1;
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85 L_s2 <<= 15;
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86
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87 /* Execution of a 31 bv 16 bits multiplication
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88 */
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89
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90 msp = SASR( L_z2, 15 );
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91 lsp = L_z2-((longword)msp<<15); /* gsm_L_sub(L_z2,(msp<<15)); */
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92
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93 L_s2 += GSM_MULT_R( lsp, 32735 );
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94 L_temp = (longword)msp * 32735; /* GSM_L_MULT(msp,32735) >> 1;*/
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95 L_z2 = GSM_L_ADD( L_temp, L_s2 );
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96
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97 /* Compute sof[k] with rounding
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98 */
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99 L_temp = GSM_L_ADD( L_z2, 16384 );
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100
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101 /* 4.2.3 Preemphasis
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102 */
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103
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104 msp = GSM_MULT_R( mp, -28180 );
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105 mp = SASR( L_temp, 15 );
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106 *so++ = GSM_ADD( mp, msp );
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107 }
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108
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109 S->z1 = z1;
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110 S->L_z2 = L_z2;
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111 S->mp = mp;
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112 }