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1 /* Version 3.01 - 31.Jan.2000
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2 =============================================================================
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3
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4 U U GGG SSS TTTTT
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5 U U G S T
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6 U U G GG SSS T
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7 U U G G S T
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8 UUUU GGG SSS T
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9
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10 ========================================
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11 ITU-T - USER'S GROUP ON SOFTWARE TOOLS
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12 ========================================
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13
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14
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15 =============================================================
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16 COPYRIGHT NOTE: This source code, and all of its derivations,
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17 is subject to the "ITU-T General Public License". Please have
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18 it read in the distribution disk, or in the ITU-T
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19 Recommendation G.191 on "SOFTWARE TOOLS FOR SPEECH AND AUDIO
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20 CODING STANDARDS".
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21 =============================================================
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22
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23
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24 MODULE: G711.C, G.711 ENCODING/DECODING FUNCTIONS
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25
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26 ORIGINAL BY:
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27
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28 Simao Ferraz de Campos Neto Rudolf Hofmann
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29 CPqD/Telebras PHILIPS KOMMUNIKATIONS INDUSTRIE AG
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30 DDS/Pr.11 Kommunikationssysteme
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31 Rd. Mogi Mirim-Campinas Km.118 Thurn-und-Taxis-Strasse 14
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32 13.085 - Campinas - SP (Brazil) D-8500 Nuernberg 10 (Germany)
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33
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34 Phone : +55-192-39-6396 Phone : +49 911 526-2603
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35 FAX : +55-192-53-4754 FAX : +49 911 526-3385
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36 EMail : tdsimao@venus.cpqd.ansp.br EMail : HF@PKINBG.UUCP
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37
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38
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39 FUNCTIONS:
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40
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41 alaw_compress: ... compands 1 vector of linear PCM samples to A-law;
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42 uses 13 Most Sig.Bits (MSBs) from input and 8 Least
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43 Sig. Bits (LSBs) on output.
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44
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45 alaw_expand: ..... expands 1 vector of A-law samples to linear PCM;
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46 use 8 Least Sig. Bits (LSBs) from input and
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47 13 Most Sig.Bits (MSBs) on output.
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48
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49 ulaw_compress: ... compands 1 vector of linear PCM samples to u-law;
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50 uses 14 Most Sig.Bits (MSBs) from input and 8 Least
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51 Sig. Bits (LSBs) on output.
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52
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53 ulaw_expand: ..... expands 1 vector of u-law samples to linear PCM
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54 use 8 Least Sig. Bits (LSBs) from input and
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55 14 Most Sig.Bits (MSBs) on output.
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56
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57 PROTOTYPES: in g711.h
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58
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59 HISTORY:
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60 Apr/91 1.0 First version of the G711 module
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61 10/Dec/1991 2.0 Break-up in individual functions for A,u law;
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62 correction of bug in compression routines (use of 1
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63 and 2 complement); Demo program inside module.
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64 08/Feb/1992 3.0 Demo as separate file;
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65 31/Jan/2000 3.01 Updated documentation text; no change in functions
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66 <simao.campos@labs.comsat.com>
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67 13jan2005 Byte for compressed data
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68 =============================================================================
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69 */
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70
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71 /*
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72 * .......... I N C L U D E S ..........
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73 */
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74
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75 /* Global prototype functions */
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76 #include "g711.h"
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77
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78 /*
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79 * .......... F U N C T I O N S ..........
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80 */
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81
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82 /* ................... Begin of alaw_compress() ..................... */
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83 /*
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84 ==========================================================================
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85
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86 FUNCTION NAME: alaw_compress
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87
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88 DESCRIPTION: ALaw encoding rule according ITU-T Rec. G.711.
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89
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90 PROTOTYPE: void alaw_compress(long lseg, short *linbuf, short *logbuf)
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91
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92 PARAMETERS:
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93 lseg: (In) number of samples
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94 linbuf: (In) buffer with linear samples (only 12 MSBits are taken
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95 into account)
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96 logbuf: (Out) buffer with compressed samples (8 bit right justified,
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97 without sign extension)
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98
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99 RETURN VALUE: none.
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100
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101 HISTORY:
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102 10.Dec.91 1.0 Separated A-law compression function
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103
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104 ==========================================================================
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105 */
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106 void alaw_compress(long lseg, short *linbuf, Byte *logbuf)
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107 {
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108 short ix, iexp;
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109 long n;
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110
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111 for (n = 0; n < lseg; n++) {
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112 ix = linbuf[n] < 0 /* 0 <= ix < 2048 */
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113 ? (~linbuf[n]) >> 4 /* 1's complement for negative values */
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114 : (linbuf[n]) >> 4;
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115
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116 /* Do more, if exponent > 0 */
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117 if (ix > 15) { /* exponent=0 for ix <= 15 */
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118 iexp = 1; /* first step: */
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119 while (ix > 16 + 15) { /* find mantissa and exponent */
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120 ix >>= 1;
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121 iexp++;
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122 }
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123 ix -= 16; /* second step: remove leading '1' */
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124
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125 ix += iexp << 4; /* now compute encoded value */
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126 }
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127 if (linbuf[n] >= 0)
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128 ix |= (0x0080); /* add sign bit */
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129
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130 logbuf[n] = ix ^ (0x0055); /* toggle even bits */
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131 }
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132 }
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133
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134 /* ................... End of alaw_compress() ..................... */
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135
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136
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137 /* ................... Begin of alaw_expand() ..................... */
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138 /*
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139 ==========================================================================
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140
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141 FUNCTION NAME: alaw_expand
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142
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143 DESCRIPTION: ALaw decoding rule according ITU-T Rec. G.711.
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144
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145 PROTOTYPE: void alaw_expand(long lseg, short *logbuf, short *linbuf)
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146
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147 PARAMETERS:
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148 lseg: (In) number of samples
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149 logbuf: (In) buffer with compressed samples (8 bit right justified,
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150 without sign extension)
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151 linbuf: (Out) buffer with linear samples (13 bits left justified)
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152
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153 RETURN VALUE: none.
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154
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155 HISTORY:
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156 10.Dec.91 1.0 Separated A-law expansion function
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157
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158 ============================================================================
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159 */
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160 void alaw_expand(long lseg, Byte *logbuf, short *linbuf)
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161 {
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162 short ix, mant, iexp;
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163 long n;
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164
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165 for (n = 0; n < lseg; n++) {
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166 ix = logbuf[n] ^ (0x0055); /* re-toggle toggled bits */
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167
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168 ix &= (0x007F); /* remove sign bit */
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169 iexp = ix >> 4; /* extract exponent */
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170 mant = ix & (0x000F); /* now get mantissa */
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171 if (iexp > 0)
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172 mant = mant + 16; /* add leading '1', if exponent > 0 */
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173
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174 mant = (mant << 4) + (0x0008); /* now mantissa left justified and */
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175 /* 1/2 quantization step added */
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176 if (iexp > 1) /* now left shift according exponent */
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177 mant = mant << (iexp - 1);
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178
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179 linbuf[n] = logbuf[n] > 127 /* invert, if negative sample */
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180 ? mant : -mant;
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181 }
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182 }
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183
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184 /* ................... End of alaw_expand() ..................... */
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185
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186
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187 /* ................... Begin of ulaw_compress() ..................... */
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188 /*
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189 ==========================================================================
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190
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191 FUNCTION NAME: ulaw_compress
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192
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193 DESCRIPTION: Mu law encoding rule according ITU-T Rec. G.711.
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194
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195 PROTOTYPE: void ulaw_compress(long lseg, short *linbuf, short *logbuf)
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196
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197 PARAMETERS:
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198 lseg: (In) number of samples
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199 linbuf: (In) buffer with linear samples (only 12 MSBits are taken
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200 into account)
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201 logbuf: (Out) buffer with compressed samples (8 bit right justified,
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202 without sign extension)
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203
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204 RETURN VALUE: none.
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205
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206 HISTORY:
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207 10.Dec.91 1.0 Separated mu-law compression function
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208
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209 ==========================================================================
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210 */
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211 void ulaw_compress(long lseg, short *linbuf, Byte *logbuf)
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212 {
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213 long n; /* samples's count */
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214 short i; /* aux.var. */
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215 short absno; /* absolute value of linear (input) sample */
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216 short segno; /* segment (Table 2/G711, column 1) */
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217 short low_nibble; /* low nibble of log companded sample */
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218 short high_nibble; /* high nibble of log companded sample */
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219
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220 for (n = 0; n < lseg; n++) {
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221 /* -------------------------------------------------------------------- */
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222 /* Change from 14 bit left justified to 14 bit right justified */
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223 /* Compute absolute value; adjust for easy processing */
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224 /* -------------------------------------------------------------------- */
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225 absno = linbuf[n] < 0 /* compute 1's complement in case of */
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226 ? ((~linbuf[n]) >> 2) + 33 /* negative samples */
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227 : ((linbuf[n]) >> 2) + 33; /* NB: 33 is the difference value */
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228 /* between the thresholds for */
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229 /* A-law and u-law. */
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230 if (absno > (0x1FFF)) /* limitation to "absno" < 8192 */
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231 absno = (0x1FFF);
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232
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233 /* Determination of sample's segment */
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234 i = absno >> 6;
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235 segno = 1;
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236 while (i != 0) {
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237 segno++;
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238 i >>= 1;
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239 }
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240
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241 /* Mounting the high-nibble of the log-PCM sample */
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242 high_nibble = (0x0008) - segno;
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243
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244 /* Mounting the low-nibble of the log PCM sample */
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245 low_nibble = (absno >> segno) /* right shift of mantissa and */
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246 &(0x000F); /* masking away leading '1' */
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247 low_nibble = (0x000F) - low_nibble;
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248
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249 /* Joining the high-nibble and the low-nibble of the log PCM sample */
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250 logbuf[n] = (high_nibble << 4) | low_nibble;
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251
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252 /* Add sign bit */
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253 if (linbuf[n] >= 0)
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254 logbuf[n] = logbuf[n] | (0x0080);
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255 }
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256 }
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257
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258 /* ................... End of ulaw_compress() ..................... */
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259
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260
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261
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262 /* ................... Begin of ulaw_expand() ..................... */
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263 /*
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264 ==========================================================================
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265
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266 FUNCTION NAME: ulaw_expand
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267
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268 DESCRIPTION: Mu law decoding rule according ITU-T Rec. G.711.
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269
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270 PROTOTYPE: void ulaw_expand(long lseg, short *logbuf, short *linbuf)
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271
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272 PARAMETERS:
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273 lseg: (In) number of samples
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274 logbuf: (In) buffer with compressed samples (8 bit right justified,
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275 without sign extension)
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276 linbuf: (Out) buffer with linear samples (14 bits left justified)
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277
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278 RETURN VALUE: none.
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279
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280 HISTORY:
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281 10.Dec.91 1.0 Separated mu law expansion function
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282
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283 ============================================================================
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284 */
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285
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286 void ulaw_expand(long lseg, Byte *logbuf, short *linbuf)
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287 {
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288 long n; /* aux.var. */
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289 short segment; /* segment (Table 2/G711, column 1) */
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290 short mantissa; /* low nibble of log companded sample */
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291 short exponent; /* high nibble of log companded sample */
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292 short sign; /* sign of output sample */
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293 short step;
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294
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295 for (n = 0; n < lseg; n++) {
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296 sign = logbuf[n] < (0x0080) /* sign-bit = 1 for positiv values */
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297 ? -1 : 1;
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298 mantissa = ~logbuf[n]; /* 1's complement of input value */
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299 exponent = (mantissa >> 4) & (0x0007); /* extract exponent */
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300 segment = exponent + 1; /* compute segment number */
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301 mantissa = mantissa & (0x000F); /* extract mantissa */
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302
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303 /* Compute Quantized Sample (14 bit left justified!) */
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304 step = (4) << segment; /* position of the LSB */
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305 /* = 1 quantization step) */
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306 linbuf[n] = sign * /* sign */
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307 (((0x0080) << exponent) /* '1', preceding the mantissa */
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308 +step * mantissa /* left shift of mantissa */
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309 + step / 2 /* 1/2 quantization step */
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310 - 4 * 33);
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311 }
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312 }
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313
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314 /* ................... End of ulaw_expand() ..................... */
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