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annotate libgsmefr/oper_32b.c @ 350:9b05bbc23b8a

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libgsmefr inline: make shift count guards 100% robust
author Mychaela Falconia <falcon@freecalypso.org>
date Tue, 23 Apr 2024 05:34:54 +0000
parents 3da7ab45910d
children
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
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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 * Function Mpy_32() *
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33 * *
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34 * Multiply two 32 bit integers (DPF). The result is divided by 2**31 *
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35 * *
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36 * L_32 = (hi1*hi2)<<1 + ( (hi1*lo2)>>15 + (lo1*hi2)>>15 )<<1 *
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37 * *
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38 * This operation can also be viewed as the multiplication of two Q31 *
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39 * number and the result is also in Q31. *
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40 * *
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41 * Arguments: *
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42 * *
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43 * hi1 hi part of first number *
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44 * lo1 lo part of first number *
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45 * hi2 hi part of second number *
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46 * lo2 lo part of second number *
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47 * *
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48 *****************************************************************************
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49 */
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50
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51 Word32 Mpy_32 (Word16 hi1, Word16 lo1, Word16 hi2, Word16 lo2)
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52 {
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53 Word32 L_32;
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54
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55 L_32 = L_mult (hi1, hi2);
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56 L_32 = L_mac (L_32, mult (hi1, lo2), 1);
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57 L_32 = L_mac (L_32, mult (lo1, hi2), 1);
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58
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59 return (L_32);
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60 }
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61
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62 /*****************************************************************************
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63 * Function Mpy_32_16() *
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64 * *
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65 * Multiply a 16 bit integer by a 32 bit (DPF). The result is divided *
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66 * by 2**15 *
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67 * *
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68 * *
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69 * L_32 = (hi1*lo2)<<1 + ((lo1*lo2)>>15)<<1 *
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70 * *
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71 * Arguments: *
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72 * *
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73 * hi hi part of 32 bit number. *
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74 * lo lo part of 32 bit number. *
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75 * n 16 bit number. *
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76 * *
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77 *****************************************************************************
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78 */
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79
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80 Word32 Mpy_32_16 (Word16 hi, Word16 lo, Word16 n)
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81 {
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82 Word32 L_32;
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83
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84 L_32 = L_mult (hi, n);
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85 L_32 = L_mac (L_32, mult (lo, n), 1);
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86
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87 return (L_32);
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88 }
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89
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90 /*****************************************************************************
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91 * *
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92 * Function Name : Div_32 *
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93 * *
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94 * Purpose : *
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95 * Fractional integer division of two 32 bit numbers. *
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96 * L_num / L_denom. *
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97 * L_num and L_denom must be positive and L_num < L_denom. *
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98 * L_denom = denom_hi<<16 + denom_lo<<1 *
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99 * denom_hi is a normalize number. *
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100 * *
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101 * Inputs : *
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102 * *
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103 * L_num *
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104 * 32 bit long signed integer (Word32) whose value falls in the *
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105 * range : 0x0000 0000 < L_num < L_denom *
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106 * *
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107 * L_denom = denom_hi<<16 + denom_lo<<1 (DPF) *
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108 * *
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109 * denom_hi *
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110 * 16 bit positive normalized integer whose value falls in the *
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111 * range : 0x4000 < hi < 0x7fff *
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112 * denom_lo *
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113 * 16 bit positive integer whose value falls in the *
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114 * range : 0 < lo < 0x7fff *
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115 * *
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116 * Return Value : *
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117 * *
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118 * L_div *
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119 * 32 bit long signed integer (Word32) whose value falls in the *
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120 * range : 0x0000 0000 <= L_div <= 0x7fff ffff. *
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121 * *
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122 * Algorithm: *
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123 * *
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124 * - find = 1/L_denom. *
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125 * First approximation: approx = 1 / denom_hi *
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126 * 1/L_denom = approx * (2.0 - L_denom * approx ) *
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127 * *
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128 * - result = L_num * (1/L_denom) *
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129 *****************************************************************************
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130 */
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131
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132 Word32 Div_32 (Word32 L_num, Word16 denom_hi, Word16 denom_lo)
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133 {
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134 Word16 approx, hi, lo, n_hi, n_lo;
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135 Word32 L_32;
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136
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137 /* First approximation: 1 / L_denom = 1/denom_hi */
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138
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139 approx = div_s ((Word16) 0x3fff, denom_hi);
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140
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141 /* 1/L_denom = approx * (2.0 - L_denom * approx) */
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142
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143 L_32 = Mpy_32_16 (denom_hi, denom_lo, approx);
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144
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145 L_32 = L_sub ((Word32) 0x7fffffffL, L_32);
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146
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147 L_Extract (L_32, &hi, &lo);
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148
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149 L_32 = Mpy_32_16 (hi, lo, approx);
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150
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151 /* L_num * (1/L_denom) */
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152
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153 L_Extract (L_32, &hi, &lo);
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154 L_Extract (L_num, &n_hi, &n_lo);
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155 L_32 = Mpy_32 (n_hi, n_lo, hi, lo);
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156 L_32 = L_shl (L_32, 2);
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157
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158 return (L_32);
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159 }