annotate libgsmefr/oper_32b.c @ 242:f081a6850fb5

libgsmfrp: new refined implementation The previous implementation exhibited the following defects, which are now fixed: 1) The last received valid SID was cached forever for the purpose of handling future invalid SIDs - we could have received some valid SID ages ago, then lots of speech or NO_DATA, and if we then get an invalid SID, we would resurrect the last valid SID from ancient history - a bad design. In our new design, we handle invalid SID based on the current state, much like BFI. 2) GSM 06.11 spec says clearly that after the second lost SID (received BFI=1 && TAF=1 in CN state) we need to gradually decrease the output level, rather than jump directly to emitting silence frames - we previously failed to implement such logic. 3) Per GSM 06.12 section 5.2, Xmaxc should be the same in all 4 subframes in a SID frame. What should we do if we receive an otherwise valid SID frame with different Xmaxc? Our previous approach would replicate this Xmaxc oddity in every subsequent generated CN frame, which is rather bad. In our new design, the very first CN frame (which can be seen as a transformation of the SID frame itself) retains the original 4 distinct Xmaxc, but all subsequent CN frames are based on the Xmaxc from the last subframe of the most recent SID.
author Mychaela Falconia <falcon@freecalypso.org>
date Tue, 09 May 2023 05:16:31 +0000
parents 92479d9a8e38
children 3da7ab45910d
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1 /*****************************************************************************
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2 * *
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3 * This file contains operations in double precision. *
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4 * These operations are not standard double precision operations. *
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5 * They are used where single precision is not enough but the full 32 bits *
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6 * precision is not necessary. For example, the function Div_32() has a *
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7 * 24 bits precision which is enough for our purposes. *
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8 * *
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9 * The double precision numbers use a special representation: *
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10 * *
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11 * L_32 = hi<<16 + lo<<1 *
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12 * *
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13 * L_32 is a 32 bit integer. *
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14 * hi and lo are 16 bit signed integers. *
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15 * As the low part also contains the sign, this allows fast multiplication. *
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16 * *
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17 * 0x8000 0000 <= L_32 <= 0x7fff fffe. *
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18 * *
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19 * We will use DPF (Double Precision Format )in this file to specify *
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20 * this special format. *
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21 *****************************************************************************
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22 */
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23
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24 #include "gsm_efr.h"
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25 #include "typedef.h"
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26 #include "namespace.h"
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27 #include "basic_op.h"
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28 #include "oper_32b.h"
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29 #include "no_count.h"
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31 /*****************************************************************************
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32 * *
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33 * Function L_Extract() *
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34 * *
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35 * Extract from a 32 bit integer two 16 bit DPF. *
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36 * *
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37 * Arguments: *
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38 * *
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39 * L_32 : 32 bit integer. *
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40 * 0x8000 0000 <= L_32 <= 0x7fff ffff. *
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41 * hi : b16 to b31 of L_32 *
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42 * lo : (L_32 - hi<<16)>>1 *
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43 *****************************************************************************
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44 */
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46 void L_Extract (Word32 L_32, Word16 *hi, Word16 *lo)
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47 {
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48 *hi = extract_h (L_32);
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49 *lo = extract_l (L_msu (L_shr (L_32, 1), *hi, 16384));
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50 return;
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51 }
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52
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53 /*****************************************************************************
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54 * *
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55 * Function L_Comp() *
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56 * *
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57 * Compose from two 16 bit DPF a 32 bit integer. *
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58 * *
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59 * L_32 = hi<<16 + lo<<1 *
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60 * *
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61 * Arguments: *
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62 * *
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63 * hi msb *
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64 * lo lsf (with sign) *
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65 * *
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66 * Return Value : *
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67 * *
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68 * 32 bit long signed integer (Word32) whose value falls in the *
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69 * range : 0x8000 0000 <= L_32 <= 0x7fff fff0. *
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70 * *
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71 *****************************************************************************
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72 */
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73
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74 Word32 L_Comp (Word16 hi, Word16 lo)
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75 {
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76 Word32 L_32;
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77
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78 L_32 = L_deposit_h (hi);
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79 return (L_mac (L_32, lo, 1)); /* = hi<<16 + lo<<1 */
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80 }
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81
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82 /*****************************************************************************
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83 * Function Mpy_32() *
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84 * *
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85 * Multiply two 32 bit integers (DPF). The result is divided by 2**31 *
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86 * *
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87 * L_32 = (hi1*hi2)<<1 + ( (hi1*lo2)>>15 + (lo1*hi2)>>15 )<<1 *
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88 * *
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89 * This operation can also be viewed as the multiplication of two Q31 *
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90 * number and the result is also in Q31. *
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91 * *
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92 * Arguments: *
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93 * *
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94 * hi1 hi part of first number *
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95 * lo1 lo part of first number *
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96 * hi2 hi part of second number *
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97 * lo2 lo part of second number *
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98 * *
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99 *****************************************************************************
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100 */
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101
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102 Word32 Mpy_32 (Word16 hi1, Word16 lo1, Word16 hi2, Word16 lo2)
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103 {
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104 Word32 L_32;
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105
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106 L_32 = L_mult (hi1, hi2);
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107 L_32 = L_mac (L_32, mult (hi1, lo2), 1);
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108 L_32 = L_mac (L_32, mult (lo1, hi2), 1);
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109
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110 return (L_32);
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111 }
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112
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113 /*****************************************************************************
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114 * Function Mpy_32_16() *
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115 * *
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116 * Multiply a 16 bit integer by a 32 bit (DPF). The result is divided *
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117 * by 2**15 *
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118 * *
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119 * *
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120 * L_32 = (hi1*lo2)<<1 + ((lo1*lo2)>>15)<<1 *
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121 * *
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122 * Arguments: *
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123 * *
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124 * hi hi part of 32 bit number. *
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125 * lo lo part of 32 bit number. *
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126 * n 16 bit number. *
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127 * *
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128 *****************************************************************************
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129 */
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130
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131 Word32 Mpy_32_16 (Word16 hi, Word16 lo, Word16 n)
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132 {
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133 Word32 L_32;
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134
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135 L_32 = L_mult (hi, n);
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136 L_32 = L_mac (L_32, mult (lo, n), 1);
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137
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138 return (L_32);
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139 }
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140
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141 /*****************************************************************************
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142 * *
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143 * Function Name : Div_32 *
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144 * *
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145 * Purpose : *
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146 * Fractional integer division of two 32 bit numbers. *
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147 * L_num / L_denom. *
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148 * L_num and L_denom must be positive and L_num < L_denom. *
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149 * L_denom = denom_hi<<16 + denom_lo<<1 *
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150 * denom_hi is a normalize number. *
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151 * *
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152 * Inputs : *
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153 * *
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154 * L_num *
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155 * 32 bit long signed integer (Word32) whose value falls in the *
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156 * range : 0x0000 0000 < L_num < L_denom *
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157 * *
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158 * L_denom = denom_hi<<16 + denom_lo<<1 (DPF) *
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159 * *
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160 * denom_hi *
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161 * 16 bit positive normalized integer whose value falls in the *
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162 * range : 0x4000 < hi < 0x7fff *
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163 * denom_lo *
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164 * 16 bit positive integer whose value falls in the *
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165 * range : 0 < lo < 0x7fff *
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166 * *
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167 * Return Value : *
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168 * *
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169 * L_div *
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170 * 32 bit long signed integer (Word32) whose value falls in the *
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171 * range : 0x0000 0000 <= L_div <= 0x7fff ffff. *
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172 * *
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173 * Algorithm: *
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174 * *
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175 * - find = 1/L_denom. *
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176 * First approximation: approx = 1 / denom_hi *
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177 * 1/L_denom = approx * (2.0 - L_denom * approx ) *
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178 * *
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179 * - result = L_num * (1/L_denom) *
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180 *****************************************************************************
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181 */
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182
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183 Word32 Div_32 (Word32 L_num, Word16 denom_hi, Word16 denom_lo)
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184 {
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185 Word16 approx, hi, lo, n_hi, n_lo;
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186 Word32 L_32;
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187
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188 /* First approximation: 1 / L_denom = 1/denom_hi */
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189
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190 approx = div_s ((Word16) 0x3fff, denom_hi);
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191
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192 /* 1/L_denom = approx * (2.0 - L_denom * approx) */
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193
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194 L_32 = Mpy_32_16 (denom_hi, denom_lo, approx);
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195
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196 L_32 = L_sub ((Word32) 0x7fffffffL, L_32);
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197
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198 L_Extract (L_32, &hi, &lo);
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199
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200 L_32 = Mpy_32_16 (hi, lo, approx);
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201
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202 /* L_num * (1/L_denom) */
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203
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204 L_Extract (L_32, &hi, &lo);
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205 L_Extract (L_num, &n_hi, &n_lo);
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206 L_32 = Mpy_32 (n_hi, n_lo, hi, lo);
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207 L_32 = L_shl (L_32, 2);
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208
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209 return (L_32);
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210 }