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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: /home/kbs/jutta/src/gsm/gsm-1.0/src/RCS/preprocess.c,v 1.1 1992/10/28 00:15:50 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, word * s, word * so)
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36 { /* [0..159] IN/OUT */
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37
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38 word z1 = S->z1;
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39 longword L_z2 = S->L_z2;
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40 word mp = S->mp;
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41
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42 word s1;
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43 longword L_s2;
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44
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45 longword L_temp;
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46
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47 word msp, lsp;
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48 word SO;
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49
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50 longword ltmp; /* for ADD */
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51 ulongword utmp; /* for L_ADD */
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52
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53 register int k = 160;
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54
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55 while (k--) {
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56
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57 /* 4.2.1 Downscaling of the input signal
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58 */
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59 SO = SASR(*s, 3) << 2;
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60 s++;
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61
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62 assert(SO >= -0x4000); /* downscaled by */
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63 assert(SO <= 0x3FFC); /* previous routine. */
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64
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65
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66 /* 4.2.2 Offset compensation
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67 *
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68 * This part implements a high-pass filter and requires extended
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69 * arithmetic precision for the recursive part of this filter.
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70 * The input of this procedure is the array so[0...159] and the
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71 * output the array sof[ 0...159 ].
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72 */
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73 /* Compute the non-recursive part
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74 */
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75
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76 s1 = SO - z1; /* s1 = gsm_sub( *so, z1 ); */
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77 z1 = SO;
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78
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79 assert(s1 != MIN_WORD);
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80
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81 /* Compute the recursive part
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82 */
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83 L_s2 = s1;
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84 L_s2 <<= 15;
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85
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86 /* Execution of a 31 bv 16 bits multiplication
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87 */
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88
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89 msp = SASR(L_z2, 15);
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90 lsp = L_z2 - ((longword) msp << 15); /* gsm_L_sub(L_z2,(msp<<15)); */
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91
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92 L_s2 += GSM_MULT_R(lsp, 32735);
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93 L_temp = (longword) msp *32735; /* GSM_L_MULT(msp,32735) >> 1; */
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94 L_z2 = GSM_L_ADD(L_temp, L_s2);
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95
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96 /* Compute sof[k] with rounding
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97 */
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98 L_temp = GSM_L_ADD(L_z2, 16384);
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99
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100 /* 4.2.3 Preemphasis
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101 */
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102
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103 msp = GSM_MULT_R(mp, -28180);
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104 mp = SASR(L_temp, 15);
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105 *so++ = GSM_ADD(mp, msp);
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106 }
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107
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108 S->z1 = z1;
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109 S->L_z2 = L_z2;
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110 S->mp = mp;
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111 }
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