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annotate libtwamr/preemph.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 3618b5cf25a6
children
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3618b5cf25a6 libtwamr: integrate preemph.c
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1 /*
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2 ********************************************************************************
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3 *
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4 * GSM AMR-NB speech codec R98 Version 7.6.0 December 12, 2001
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5 * R99 Version 3.3.0
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6 * REL-4 Version 4.1.0
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7 *
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8 ********************************************************************************
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9 *
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10 * File : preemph.c
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11 * Purpose : Preemphasis filtering
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12 * Description : Filtering through 1 - g z^-1
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13 *
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14 ********************************************************************************
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15 */
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16
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17 /*
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18 ********************************************************************************
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19 * MODULE INCLUDE FILE AND VERSION ID
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20 ********************************************************************************
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21 */
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22 #include "namespace.h"
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23 #include "preemph.h"
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24
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25 /*
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26 ********************************************************************************
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27 * INCLUDE FILES
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28 ********************************************************************************
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29 */
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30 #include "typedef.h"
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31 #include "basic_op.h"
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32 #include "no_count.h"
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33
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34 /*
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35 ********************************************************************************
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36 * LOCAL VARIABLES AND TABLES
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37 ********************************************************************************
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38 */
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39
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40 /*
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41 ********************************************************************************
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42 * PUBLIC PROGRAM CODE
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43 ********************************************************************************
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44 */
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45
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46 /*************************************************************************
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47 *
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48 * Function: preemphasis_reset
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49 * Purpose: Initializes state memory to zero
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50 *
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51 **************************************************************************
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52 */
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53 void preemphasis_reset (preemphasisState *state)
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54 {
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55 state->mem_pre = 0;
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56 }
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57
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58 /*
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59 **************************************************************************
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60 * Function: preemphasis
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61 * Purpose: Filtering through 1 - g z^-1
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62 *
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63 **************************************************************************
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64 */
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65 int preemphasis (
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66 preemphasisState *st, /* (i/o) : preemphasis filter state */
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67 Word16 *signal, /* (i/o) : input signal overwritten by the output */
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68 Word16 g, /* (i) : preemphasis coefficient */
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69 Word16 L /* (i) : size of filtering */
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70 )
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71 {
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72 Word16 *p1, *p2, temp, i;
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73
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74 p1 = signal + L - 1; move16 ();
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75 p2 = p1 - 1; move16 ();
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76 temp = *p1; move16 ();
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77
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78 for (i = 0; i <= L - 2; i++)
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79 {
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80 *p1 = sub (*p1, mult (g, *p2--)); move16 ();
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81 p1--;
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82 }
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83
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84 *p1 = sub (*p1, mult (g, st->mem_pre)); move16 ();
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85
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86 st->mem_pre = temp; move16 ();
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87
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88 return 0;
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89 }