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annotate libgsmfr2/preprocess.c @ 282:9ee8ad3d4d30

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frtest: rm gsmfr-hand-test and gsmfr-max-out utils These hack programs were never properly documented and were written only as part of a debug chase, in pursuit of a bug that ultimately turned out to be in our then-hacky patch to osmo-bts-sysmo, before beginning of proper patches in Osmocom. These hack programs need to be dropped from the present sw package because they depend on old libgsm, and we are eliminating that dependency.
author Mychaela Falconia <falcon@freecalypso.org>
date Sun, 14 Apr 2024 05:44:47 +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 }