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1 /*
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2 * Copyright 1992 by Jutta Degener and Carsten Bormann, Technische
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3 * Universitaet Berlin. See the accompanying file "COPYRIGHT" for
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4 * details. THERE IS ABSOLUTELY NO WARRANTY FOR THIS SOFTWARE.
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5 */
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6
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7 /* $Header: /home/kbs/jutta/src/gsm/gsm-1.0/src/RCS/add.c,v 1.2 1993/01/29 18:23:15 jutta Exp $ */
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8
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9 /*
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10 * See private.h for the more commonly used macro versions.
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11 */
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12
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13 #include <stdio.h>
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14 #include <assert.h>
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15
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16 #include "private.h"
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17 #include "gsm.h"
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18 #include "proto.h"
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19
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20 #define saturate(x) \
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21 ((x) < MIN_WORD ? MIN_WORD : (x) > MAX_WORD ? MAX_WORD: (x))
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22
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23 word gsm_add P2((a, b), word a, word b)
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24 {
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25 longword sum = (longword) a + (longword) b;
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26 return saturate(sum);
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27 }
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28
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29 word gsm_sub P2((a, b), word a, word b)
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30 {
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31 longword diff = (longword) a - (longword) b;
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32 return saturate(diff);
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33 }
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34
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35 word gsm_mult P2((a, b), word a, word b)
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36 {
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37 if (a == MIN_WORD && b == MIN_WORD)
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38 return MAX_WORD;
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39 else
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40 return (word) (SASR((longword) a * (longword) b, 15));
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41 }
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42
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43 word gsm_mult_r P2((a, b), word a, word b)
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44 {
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45 if (b == MIN_WORD && a == MIN_WORD)
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46 return MAX_WORD;
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47 else {
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48 longword prod = (longword) a * (longword) b + 16384;
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49 prod >>= 15;
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50 return prod & 0xFFFF;
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51 }
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52 }
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53
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54 word gsm_abs P1((a), word a)
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55 {
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56 return a < 0 ? (a == MIN_WORD ? MAX_WORD : -a) : a;
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57 }
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58
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59 longword gsm_L_mult P2((a, b), word a, word b)
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60 {
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61 assert(a != MIN_WORD || b != MIN_WORD);
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62 return ((longword) a * (longword) b) << 1;
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63 }
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64
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65 longword gsm_L_add P2((a, b), longword a, longword b)
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66 {
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67 if (a < 0) {
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68 if (b >= 0)
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69 return a + b;
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70 else {
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71 ulongword A = (ulongword) - (a + 1) + (ulongword) - (b + 1);
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72 return A >=
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73 (ulongword) MAX_LONGWORD ? MIN_LONGWORD : -(longword) A - 2;
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74 }
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75 } else if (b <= 0)
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76 return a + b;
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77 else {
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78 ulongword A = (ulongword) a + (ulongword) b;
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79 return A > (ulongword) MAX_LONGWORD ? MAX_LONGWORD : A;
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80 }
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81 }
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82
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83 longword gsm_L_sub P2((a, b), longword a, longword b)
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84 {
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85 if (a >= 0) {
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86 if (b >= 0)
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87 return a - b;
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88 else {
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89 /* a>=0, b<0 */
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90
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91 ulongword A = (ulongword) a + -(b + 1);
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92 return A >= (ulongword) MAX_LONGWORD ? MAX_LONGWORD : (A + 1);
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93 }
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94 } else if (b <= 0)
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95 return a - b;
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96 else {
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97 /* a<0, b>0 */
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98
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99 ulongword A = (ulongword) - (a + 1) + b;
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100 return A >= (ulongword) MAX_LONGWORD ? MIN_LONGWORD : -A - 1;
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101 }
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102 }
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103
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104 static unsigned char bitoff[256] = {
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105 8, 7, 6, 6, 5, 5, 5, 5, 4, 4, 4, 4, 4, 4, 4, 4,
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106 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
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107 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
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108 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
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109 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
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110 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
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111 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
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112 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
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113 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
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114 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
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115 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
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116 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
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117 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
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118 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
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119 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
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120 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
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121 };
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122
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123 word gsm_norm P1((a), longword a)
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124 /*
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125 * the number of left shifts needed to normalize the 32 bit
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126 * variable L_var1 for positive values on the interval
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127 *
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128 * with minimum of
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129 * minimum of 1073741824 (01000000000000000000000000000000) and
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130 * maximum of 2147483647 (01111111111111111111111111111111)
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131 *
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132 *
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133 * and for negative values on the interval with
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134 * minimum of -2147483648 (-10000000000000000000000000000000) and
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135 * maximum of -1073741824 ( -1000000000000000000000000000000).
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136 *
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137 * in order to normalize the result, the following
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138 * operation must be done: L_norm_var1 = L_var1 << norm( L_var1 );
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139 *
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140 * (That's 'ffs', only from the left, not the right..)
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141 */
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142 {
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143 assert(a != 0);
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144
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145 if (a < 0) {
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146 if (a <= (longword) - 1073741824)
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147 return 0;
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148 a = ~a;
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149 }
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150
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151 return a & 0xffff0000
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152 ? (a & 0xff000000 ? -1 + bitoff[(unsigned char) (0xFF & (a >> 24))]
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153 : 7 + bitoff[(unsigned char) (0xFF & (a >> 16))])
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154 : (a & 0xff00 ? 15 + bitoff[(unsigned char) (0xFF & (a >> 8))]
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155 : 23 + bitoff[(unsigned char) (0xFF & a)]);
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156 }
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157
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158 longword gsm_L_asl P2((a, n), longword a, int n)
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159 {
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160 if (n >= 32)
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161 return 0;
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162 if (n <= -32)
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163 return -(a < 0);
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164 if (n < 0)
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165 return gsm_asr(a, -n);
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166 return a << n;
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167 }
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168
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169 word gsm_asl P2((a, n), word a, int n)
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170 {
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171 if (n >= 16)
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172 return 0;
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173 if (n <= -16)
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174 return -(a < 0);
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175 if (n < 0)
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176 return gsm_asr(a, -n);
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177 return a << n;
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178 }
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179
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180 longword gsm_L_asr P2((a, n), longword a, int n)
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181 {
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182 if (n >= 32)
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183 return -(a < 0);
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184 if (n <= -32)
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185 return 0;
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186 if (n < 0)
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187 return a << -n;
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188
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189 # ifdef SASR
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190 return a >> n;
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191 # else
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192 if (a >= 0)
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193 return a >> n;
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194 else
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195 return -(longword) (-(ulongword) a >> n);
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196 # endif
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197 }
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198
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199 word gsm_asr P2((a, n), word a, int n)
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200 {
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201 if (n >= 16)
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202 return -(a < 0);
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203 if (n <= -16)
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204 return 0;
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205 if (n < 0)
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206 return a << -n;
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207
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208 # ifdef SASR
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209 return a >> n;
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210 # else
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211 if (a >= 0)
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212 return a >> n;
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213 else
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214 return -(word) (-(uword) a >> n);
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215 # endif
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216 }
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217
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218 /*
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219 * (From p. 46, end of section 4.2.5)
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220 *
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221 * NOTE: The following lines gives [sic] one correct implementation
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222 * of the div(num, denum) arithmetic operation. Compute div
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223 * which is the integer division of num by denum: with denum
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224 * >= num > 0
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225 */
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226
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227 word gsm_div P2((num, denum), word num, word denum)
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228 {
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229 longword L_num = num;
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230 longword L_denum = denum;
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231 word div = 0;
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232 int k = 15;
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233
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234 /* The parameter num sometimes becomes zero.
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235 * Although this is explicitly guarded against in 4.2.5,
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236 * we assume that the result should then be zero as well.
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237 */
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238
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239 /* assert(num != 0); */
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240
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241 assert(num >= 0 && denum >= num);
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242 if (num == 0)
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243 return 0;
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244
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245 while (k--) {
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246 div <<= 1;
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247 L_num <<= 1;
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248
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249 if (L_num >= L_denum) {
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250 L_num -= L_denum;
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251 div++;
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252 }
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253 }
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254
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255 return div;
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256 }
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