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5
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1 /*
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2 * SpanDSP - a series of DSP components for telephony
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3 *
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4 * gsm0610_preprocess.c - GSM 06.10 full rate speech codec.
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5 *
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6 * Written by Steve Underwood <steveu@coppice.org>
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7 *
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8 * Copyright (C) 2006 Steve Underwood
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9 *
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10 * All rights reserved.
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11 *
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12 * This program is free software; you can redistribute it and/or modify
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13 * it under the terms of the GNU General Public License version 2, as
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14 * published by the Free Software Foundation.
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15 *
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16 * This program is distributed in the hope that it will be useful,
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17 * but WITHOUT ANY WARRANTY; without even the implied warranty of
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18 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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19 * GNU General Public License for more details.
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20 *
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21 * You should have received a copy of the GNU General Public License
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22 * along with this program; if not, write to the Free Software
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23 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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24 *
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25 * This code is based on the widely used GSM 06.10 code available from
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26 * http://kbs.cs.tu-berlin.de/~jutta/toast.html
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27 *
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28 * $Id: gsm0610_preprocess.c,v 1.7 2006/11/19 14:07:24 steveu Exp $
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29 */
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30
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31 /*! \file */
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32
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33 #ifdef HAVE_CONFIG_H
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34 #include <config.h>
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35 #endif
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36
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37 #include <assert.h>
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38 #include <inttypes.h>
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39 #if defined(HAVE_TGMATH_H)
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40 #include <tgmath.h>
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41 #endif
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42 #if defined(HAVE_MATH_H)
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43 #include <math.h>
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44 #endif
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45 #include <stdlib.h>
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46
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47 #include "spandsp/telephony.h"
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48 #include "spandsp/dc_restore.h"
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49 #include "spandsp/gsm0610.h"
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50
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51 #include "gsm0610_local.h"
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52
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53 /*
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54 4.2.0 .. 4.2.3 PREPROCESSING SECTION
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55
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56 After A-law to linear conversion (or directly from the
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57 A to D converter) the following scaling is assumed for
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58 input to the RPE-LTP algorithm:
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59
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60 in: 0.1.....................12
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61 S.v.v.v.v.v.v.v.v.v.v.v.v.*.*.*
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62
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63 Where S is the sign bit, v a valid bit, and * a "don't care" bit.
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64 The original signal is called sop[..]
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65
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66 out: 0.1................... 12
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67 S.S.v.v.v.v.v.v.v.v.v.v.v.v.0.0
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68 */
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69
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70 void gsm0610_preprocess(gsm0610_state_t *s, const int16_t amp[GSM0610_FRAME_LEN], int16_t so[GSM0610_FRAME_LEN])
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71 {
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72 int16_t z1;
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73 int16_t mp;
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74 int16_t s1;
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75 int16_t msp;
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76 int16_t SO;
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77 int32_t L_z2;
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78 int32_t L_s2;
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79 int32_t L_temp;
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80 #if !defined(__GNUC__)
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81 int16_t lsp;
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82 #endif
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83 int k;
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84
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85 z1 = s->z1;
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86 L_z2 = s->L_z2;
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87 mp = s->mp;
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88 for (k = 0; k < GSM0610_FRAME_LEN; k++)
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89 {
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90 /* 4.2.1 Downscaling of the input signal */
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91 SO = (amp[k] >> 1) & ~3;
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92
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93 assert(SO >= -0x4000); // downscaled by
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94 assert(SO <= 0x3FFC); // previous routine.
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95
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96 /* 4.2.2 Offset compensation */
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97
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98 /* This part implements a high-pass filter and requires extended
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99 arithmetic precision for the recursive part of this filter.
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100 The input of this procedure is the array so[0...159] and the
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101 output the array sof[ 0...159 ].
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102 */
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103 /* Compute the non-recursive part */
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104 s1 = SO - z1;
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105 z1 = SO;
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106
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107 assert(s1 != INT16_MIN);
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108
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109 /* Compute the recursive part */
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110 L_s2 = s1;
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111 L_s2 <<= 15;
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112
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113 /* Perform a 31 by 16 bits multiplication */
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114 #if defined(__GNUC__)
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115 L_z2 = ((int64_t) L_z2*32735 + 0x4000) >> 15;
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116 /* Alternate (ANSI) version of below line does slightly different rounding:
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117 * L_temp = L_z2 >> 9;
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118 * L_temp += L_temp >> 5;
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119 * L_temp = (++L_temp) >> 1;
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120 * L_z2 = L_z2 - L_temp;
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121 */
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122 L_z2 = gsm_l_add(L_z2, L_s2);
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123 #else
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124 /* This does L_z2 = L_z2 * 0x7FD5/0x8000 + L_s2 */
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125 msp = (int16_t) (L_z2 >> 15);
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126 lsp = (int16_t) (L_z2 - ((int32_t) msp << 15));
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127
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128 L_s2 += gsm_mult_r(lsp, 32735);
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129 L_temp = (int32_t) msp*32735;
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130 L_z2 = gsm_l_add(L_temp, L_s2);
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131 #endif
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132
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133 /* Compute sof[k] with rounding */
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134 L_temp = gsm_l_add(L_z2, 16384);
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135
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136 /* 4.2.3 Preemphasis */
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137 msp = gsm_mult_r(mp, -28180);
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138 mp = (int16_t) (L_temp >> 15);
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139 so[k] = gsm_add(mp, msp);
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140 }
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141 /*endfor*/
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142
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143 s->z1 = z1;
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144 s->L_z2 = L_z2;
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145 s->mp = mp;
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146 }
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147 /*- End of function --------------------------------------------------------*/
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148 /*- End of file ------------------------------------------------------------*/
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