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annotate libgsmefr/oper_32b.c @ 53:49dd1ac8e75b

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libgsmefr: import most *.c files from ETSI source
author Mychaela Falconia <falcon@freecalypso.org>
date Fri, 25 Nov 2022 16:18:21 +0000
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children 92479d9a8e38
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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 "typedef.h"
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25 #include "basic_op.h"
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26 #include "oper_32b.h"
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27 #include "count.h"
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28
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29 /*****************************************************************************
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30 * *
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31 * Function L_Extract() *
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32 * *
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33 * Extract from a 32 bit integer two 16 bit DPF. *
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34 * *
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35 * Arguments: *
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36 * *
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37 * L_32 : 32 bit integer. *
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38 * 0x8000 0000 <= L_32 <= 0x7fff ffff. *
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39 * hi : b16 to b31 of L_32 *
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40 * lo : (L_32 - hi<<16)>>1 *
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41 *****************************************************************************
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42 */
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43
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44 void L_Extract (Word32 L_32, Word16 *hi, Word16 *lo)
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45 {
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46 *hi = extract_h (L_32);
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47 *lo = extract_l (L_msu (L_shr (L_32, 1), *hi, 16384));
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48 return;
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49 }
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50
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51 /*****************************************************************************
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52 * *
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53 * Function L_Comp() *
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54 * *
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55 * Compose from two 16 bit DPF a 32 bit integer. *
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56 * *
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57 * L_32 = hi<<16 + lo<<1 *
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58 * *
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59 * Arguments: *
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60 * *
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61 * hi msb *
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62 * lo lsf (with sign) *
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63 * *
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64 * Return Value : *
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65 * *
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66 * 32 bit long signed integer (Word32) whose value falls in the *
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67 * range : 0x8000 0000 <= L_32 <= 0x7fff fff0. *
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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 Word32 L_Comp (Word16 hi, Word16 lo)
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73 {
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74 Word32 L_32;
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75
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76 L_32 = L_deposit_h (hi);
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77 return (L_mac (L_32, lo, 1)); /* = hi<<16 + lo<<1 */
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78 }
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79
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80 /*****************************************************************************
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81 * Function Mpy_32() *
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82 * *
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83 * Multiply two 32 bit integers (DPF). The result is divided by 2**31 *
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84 * *
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85 * L_32 = (hi1*hi2)<<1 + ( (hi1*lo2)>>15 + (lo1*hi2)>>15 )<<1 *
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86 * *
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87 * This operation can also be viewed as the multiplication of two Q31 *
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88 * number and the result is also in Q31. *
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89 * *
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90 * Arguments: *
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91 * *
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92 * hi1 hi part of first number *
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93 * lo1 lo part of first number *
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94 * hi2 hi part of second number *
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95 * lo2 lo part of second number *
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96 * *
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97 *****************************************************************************
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98 */
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99
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100 Word32 Mpy_32 (Word16 hi1, Word16 lo1, Word16 hi2, Word16 lo2)
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101 {
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102 Word32 L_32;
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103
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104 L_32 = L_mult (hi1, hi2);
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105 L_32 = L_mac (L_32, mult (hi1, lo2), 1);
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106 L_32 = L_mac (L_32, mult (lo1, hi2), 1);
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107
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108 return (L_32);
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109 }
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110
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111 /*****************************************************************************
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112 * Function Mpy_32_16() *
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113 * *
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114 * Multiply a 16 bit integer by a 32 bit (DPF). The result is divided *
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115 * by 2**15 *
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116 * *
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117 * *
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118 * L_32 = (hi1*lo2)<<1 + ((lo1*lo2)>>15)<<1 *
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119 * *
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120 * Arguments: *
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121 * *
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122 * hi hi part of 32 bit number. *
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123 * lo lo part of 32 bit number. *
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124 * n 16 bit number. *
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125 * *
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126 *****************************************************************************
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127 */
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128
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129 Word32 Mpy_32_16 (Word16 hi, Word16 lo, Word16 n)
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130 {
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131 Word32 L_32;
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132
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133 L_32 = L_mult (hi, n);
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134 L_32 = L_mac (L_32, mult (lo, n), 1);
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135
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136 return (L_32);
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137 }
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138
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139 /*****************************************************************************
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140 * *
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141 * Function Name : Div_32 *
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142 * *
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143 * Purpose : *
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144 * Fractional integer division of two 32 bit numbers. *
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145 * L_num / L_denom. *
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146 * L_num and L_denom must be positive and L_num < L_denom. *
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147 * L_denom = denom_hi<<16 + denom_lo<<1 *
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148 * denom_hi is a normalize number. *
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149 * *
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150 * Inputs : *
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151 * *
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152 * L_num *
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153 * 32 bit long signed integer (Word32) whose value falls in the *
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154 * range : 0x0000 0000 < L_num < L_denom *
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155 * *
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156 * L_denom = denom_hi<<16 + denom_lo<<1 (DPF) *
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157 * *
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158 * denom_hi *
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159 * 16 bit positive normalized integer whose value falls in the *
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160 * range : 0x4000 < hi < 0x7fff *
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161 * denom_lo *
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162 * 16 bit positive integer whose value falls in the *
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163 * range : 0 < lo < 0x7fff *
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164 * *
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165 * Return Value : *
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166 * *
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167 * L_div *
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168 * 32 bit long signed integer (Word32) whose value falls in the *
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169 * range : 0x0000 0000 <= L_div <= 0x7fff ffff. *
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170 * *
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171 * Algorithm: *
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172 * *
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173 * - find = 1/L_denom. *
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174 * First approximation: approx = 1 / denom_hi *
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175 * 1/L_denom = approx * (2.0 - L_denom * approx ) *
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176 * *
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177 * - result = L_num * (1/L_denom) *
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178 *****************************************************************************
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179 */
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180
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181 Word32 Div_32 (Word32 L_num, Word16 denom_hi, Word16 denom_lo)
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182 {
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183 Word16 approx, hi, lo, n_hi, n_lo;
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184 Word32 L_32;
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185
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186 /* First approximation: 1 / L_denom = 1/denom_hi */
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187
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188 approx = div_s ((Word16) 0x3fff, denom_hi);
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189
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190 /* 1/L_denom = approx * (2.0 - L_denom * approx) */
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191
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192 L_32 = Mpy_32_16 (denom_hi, denom_lo, approx);
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193
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194 L_32 = L_sub ((Word32) 0x7fffffffL, L_32);
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195
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196 L_Extract (L_32, &hi, &lo);
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197
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198 L_32 = Mpy_32_16 (hi, lo, approx);
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199
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200 /* L_num * (1/L_denom) */
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201
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202 L_Extract (L_32, &hi, &lo);
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203 L_Extract (L_num, &n_hi, &n_lo);
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204 L_32 = Mpy_32 (n_hi, n_lo, hi, lo);
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205 L_32 = L_shl (L_32, 2);
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206
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207 return (L_32);
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208 }