FreeCalypso > hg > gsmhr-codec-ref

annotate mathdp31.c @ 6:9cbb19619a9f default tip

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README: punctuation fix
author Mychaela Falconia <falcon@freecalypso.org>
date Tue, 20 Aug 2024 19:00:23 +0000
parents 9008dbc8ca74
children
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1 /***************************************************************************
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2 *
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3 * File Name: mathdp31.c
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4 *
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5 * Purpose: Contains functions increased-precision arithmetic operations.
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6 *
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7 * Below is a listing of all the functions in this file. There
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8 * is no interdependence among the functions.
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9 *
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10 * L_mpy_ls()
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11 * L_mpy_ll()
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12 * isLwLimit()
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13 * isSwLimit()
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14 *
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15 ***************************************************************************/
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16 /*_________________________________________________________________________
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17 | |
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18 | Include Files |
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19 |_________________________________________________________________________|
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20 */
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21
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22 #include "mathhalf.h"
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23 #include "typedefs.h"
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24
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25 /****************************************************************************
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26 *
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27 * FUNCTION NAME: isLwLimit
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28 *
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29 * PURPOSE:
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30 *
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31 * Check to see if the input Longword is at the
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32 * upper or lower limit of its range. i.e.
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33 * 0x7fff ffff or -0x8000 0000
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34 *
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35 * Ostensibly this is a check for an overflow.
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36 * This does not truly mean an overflow occurred,
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37 * it means the value reached is the
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38 * maximum/minimum value representable. It may
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39 * have come about due to an overflow.
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40 *
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41 * INPUTS:
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42 *
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43 * L_In A Longword input variable
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44 *
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45 *
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46 * OUTPUTS: none
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47 *
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48 * RETURN VALUE: 1 if input == 0x7fff ffff or -0x8000 0000
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49 * 0 otherwise
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50 *
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51 * KEYWORDS: saturation, limit
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52 *
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53 ***************************************************************************/
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54
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55 short isLwLimit(Longword L_In)
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56 {
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57
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58 Longword L_ls;
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59 short siOut;
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60
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61 if (L_In != 0)
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62 {
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63 L_ls = L_shl(L_In, 1);
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64 if (L_sub(L_In, L_ls) == 0)
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65 siOut = 1;
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66 else
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67 siOut = 0;
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68 }
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69 else
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70 {
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71 siOut = 0;
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72 }
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73 return (siOut);
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74 }
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75
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76 /****************************************************************************
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77 *
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78 * FUNCTION NAME: isSwLimit
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79 *
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80 * PURPOSE:
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81 *
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82 * Check to see if the input Shortword is at the
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83 * upper or lower limit of its range. i.e.
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84 * 0x7fff or -0x8000
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85 *
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86 * Ostensibly this is a check for an overflow.
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87 * This does not truly mean an overflow occurred,
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88 * it means the value reached is the
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89 * maximum/minimum value representable. It may
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90 * have come about due to an overflow.
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91 *
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92 * INPUTS:
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93 *
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94 * swIn A Shortword input variable
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95 *
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96 *
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97 * OUTPUTS: none
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98 *
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99 * RETURN VALUE: 1 if input == 0x7fff or -0x8000
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100 * 0 otherwise
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101 *
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102 * KEYWORDS: saturation, limit
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103 *
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104 ***************************************************************************/
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105
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106 short isSwLimit(Shortword swIn)
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107 {
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108
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109 Shortword swls;
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110 short siOut;
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111
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112 if (swIn != 0)
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113 {
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114 swls = shl(swIn, 1);
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115 if (sub(swIn, swls) == 0) /* logical compare outputs 1/0 */
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116 siOut = 1;
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117 else
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118 siOut = 0;
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119 }
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120 else
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121 {
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122 siOut = 0;
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123 }
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124 return (siOut);
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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 *
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130 * FUNCTION NAME: L_mpy_ll
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131 *
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132 * PURPOSE: Multiply a 32 bit number (L_var1) and a 32 bit number
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133 * (L_var2), and return a 32 bit result.
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134 *
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135 * INPUTS:
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136 *
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137 * L_var1 A Longword input variable
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138 *
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139 * L_var2 A Longword input variable
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140 *
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141 * OUTPUTS: none
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142 *
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143 * IMPLEMENTATION:
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144 *
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145 * Performs a 31x31 bit multiply, Complexity=24 Ops.
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146 *
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147 * Let x1x0, or y1y0, be the two constituent halves
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148 * of a 32 bit number. This function performs the
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149 * following:
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150 *
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151 * low = ((x0 >> 1)*(y0 >> 1)) >> 16 (low * low)
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152 * mid1 = [(x1 * (y0 >> 1)) >> 1 ] (high * low)
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153 * mid2 = [(y1 * (x0 >> 1)) >> 1] (high * low)
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154 * mid = (mid1 + low + mid2) >> 14 (sum so far)
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155 * output = (y1*x1) + mid (high * high)
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156 *
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157 *
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158 * RETURN VALUE: A Longword value
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159 *
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160 * KEYWORDS: mult,mpy,multiplication
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161 *
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162 ***************************************************************************/
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163
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164 Longword L_mpy_ll(Longword L_var1, Longword L_var2)
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165 {
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166 Shortword swLow1,
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167 swLow2,
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168 swHigh1,
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169 swHigh2;
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170 Longword L_varOut,
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171 L_low,
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172 L_mid1,
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173 L_mid2,
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174 L_mid;
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175
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176
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177 swLow1 = shr(extract_l(L_var1), 1);
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178 swLow1 = SW_MAX & swLow1;
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179
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180 swLow2 = shr(extract_l(L_var2), 1);
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181 swLow2 = SW_MAX & swLow2;
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182 swHigh1 = extract_h(L_var1);
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183 swHigh2 = extract_h(L_var2);
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184
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185 L_low = L_mult(swLow1, swLow2);
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186 L_low = L_shr(L_low, 16);
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187
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188 L_mid1 = L_mult(swHigh1, swLow2);
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189 L_mid1 = L_shr(L_mid1, 1);
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190 L_mid = L_add(L_mid1, L_low);
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191
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192 L_mid2 = L_mult(swHigh2, swLow1);
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193 L_mid2 = L_shr(L_mid2, 1);
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194 L_mid = L_add(L_mid, L_mid2);
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195
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196 L_mid = L_shr(L_mid, 14);
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197 L_varOut = L_mac(L_mid, swHigh1, swHigh2);
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198
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199 return (L_varOut);
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200 }
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201
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202 /****************************************************************************
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203 *
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204 * FUNCTION NAME: L_mpy_ls
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205 *
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206 * PURPOSE: Multiply a 32 bit number (L_var2) and a 16 bit
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207 * number (var1) returning a 32 bit result. L_var2
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208 * is truncated to 31 bits prior to executing the
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209 * multiply.
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210 *
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211 * INPUTS:
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212 *
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213 * L_var2 A Longword input variable
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214 *
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215 * var1 A Shortword input variable
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216 *
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217 * OUTPUTS: none
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218 *
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219 * RETURN VALUE: A Longword value
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220 *
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221 * KEYWORDS: mult,mpy,multiplication
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222 *
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223 ***************************************************************************/
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224
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225 Longword L_mpy_ls(Longword L_var2, Shortword var1)
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226 {
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227 Longword L_varOut;
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228 Shortword swtemp;
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229
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230 swtemp = shr(extract_l(L_var2), 1);
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231 swtemp = (short) 32767 & (short) swtemp;
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232
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233 L_varOut = L_mult(var1, swtemp);
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234 L_varOut = L_shr(L_varOut, 15);
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235 L_varOut = L_mac(L_varOut, var1, extract_h(L_var2));
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236 return (L_varOut);
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237 }