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1 /* |
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2 * Copyright 1992 by Jutta Degener and Carsten Bormann, Technische |
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3 * Universitaet Berlin. See the accompanying file "COPYRIGHT" for |
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4 * details. THERE IS ABSOLUTELY NO WARRANTY FOR THIS SOFTWARE. |
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5 */ |
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6 |
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7 /* $Header: /tmp_amd/presto/export/kbs/jutta/src/gsm/RCS/preprocess.c,v 1.2 1994/05/10 20:18:45 jutta Exp $ */ |
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8 |
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9 #include <stdio.h> |
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10 #include <assert.h> |
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11 |
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12 #include "private.h" |
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13 |
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14 #include "gsm.h" |
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15 #include "proto.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 |
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34 void Gsm_Preprocess P3((S, s, so), |
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35 struct gsm_state * S, |
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36 word * s, |
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37 word * so ) /* [0..159] IN/OUT */ |
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38 { |
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39 |
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40 word z1 = S->z1; |
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41 longword L_z2 = S->L_z2; |
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42 word mp = S->mp; |
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43 |
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44 word s1; |
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45 longword L_s2; |
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46 |
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47 longword L_temp; |
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48 |
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49 word msp, lsp; |
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50 word SO; |
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51 |
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52 longword ltmp; /* for ADD */ |
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53 ulongword utmp; /* for L_ADD */ |
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54 |
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55 register int k = 160; |
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56 |
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57 while (k--) { |
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58 |
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59 /* 4.2.1 Downscaling of the input signal |
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60 */ |
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61 SO = SASR( *s, 3 ) << 2; |
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62 s++; |
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63 |
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64 assert (SO >= -0x4000); /* downscaled by */ |
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65 assert (SO <= 0x3FFC); /* previous routine. */ |
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66 |
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67 |
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68 /* 4.2.2 Offset compensation |
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69 * |
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70 * This part implements a high-pass filter and requires extended |
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71 * arithmetic precision for the recursive part of this filter. |
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72 * The input of this procedure is the array so[0...159] and the |
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73 * output the array sof[ 0...159 ]. |
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74 */ |
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75 /* Compute the non-recursive part |
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76 */ |
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77 |
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78 s1 = SO - z1; /* s1 = gsm_sub( *so, z1 ); */ |
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79 z1 = SO; |
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80 |
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81 assert(s1 != MIN_WORD); |
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82 |
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83 /* Compute the recursive part |
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84 */ |
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85 L_s2 = s1; |
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86 L_s2 <<= 15; |
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87 |
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88 /* Execution of a 31 bv 16 bits multiplication |
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89 */ |
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90 |
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91 msp = SASR( L_z2, 15 ); |
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92 lsp = L_z2-((longword)msp<<15); /* gsm_L_sub(L_z2,(msp<<15)); */ |
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93 |
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94 L_s2 += GSM_MULT_R( lsp, 32735 ); |
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95 L_temp = (longword)msp * 32735; /* GSM_L_MULT(msp,32735) >> 1;*/ |
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96 L_z2 = GSM_L_ADD( L_temp, L_s2 ); |
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97 |
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98 /* Compute sof[k] with rounding |
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99 */ |
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100 L_temp = GSM_L_ADD( L_z2, 16384 ); |
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101 |
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102 /* 4.2.3 Preemphasis |
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103 */ |
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104 |
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105 msp = GSM_MULT_R( mp, -28180 ); |
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106 mp = SASR( L_temp, 15 ); |
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107 *so++ = GSM_ADD( mp, msp ); |
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108 } |
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109 |
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110 S->z1 = z1; |
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111 S->L_z2 = L_z2; |
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112 S->mp = mp; |
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113 } |