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annotate libgsmefr/oper_32b.c @ 122:b33f2168fdec

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doc/EFR-rationale article written
author Mychaela Falconia <falcon@freecalypso.org>
date Sat, 10 Dec 2022 08:51:01 +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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30
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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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45
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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 }