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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: /tmp_amd/presto/export/kbs/jutta/src/gsm/RCS/add.c,v 1.6 1996/07/02 09:57:33 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) return MAX_WORD; |
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38 else return SASR( (longword)a * (longword)b, 15 ); |
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39 } |
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40 |
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41 word gsm_mult_r P2((a,b), word a, word b) |
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42 { |
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43 if (b == MIN_WORD && a == MIN_WORD) return MAX_WORD; |
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44 else { |
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45 longword prod = (longword)a * (longword)b + 16384; |
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46 prod >>= 15; |
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47 return prod & 0xFFFF; |
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48 } |
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49 } |
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50 |
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51 word gsm_abs P1((a), word a) |
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52 { |
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53 return a < 0 ? (a == MIN_WORD ? MAX_WORD : -a) : a; |
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54 } |
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55 |
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56 longword gsm_L_mult P2((a,b),word a, word b) |
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57 { |
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58 assert( a != MIN_WORD || b != MIN_WORD ); |
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59 return ((longword)a * (longword)b) << 1; |
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60 } |
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61 |
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62 longword gsm_L_add P2((a,b), longword a, longword b) |
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63 { |
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64 if (a < 0) { |
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65 if (b >= 0) return a + b; |
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66 else { |
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67 ulongword A = (ulongword)-(a + 1) + (ulongword)-(b + 1); |
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68 return A >= MAX_LONGWORD ? MIN_LONGWORD :-(longword)A-2; |
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69 } |
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70 } |
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71 else if (b <= 0) return a + b; |
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72 else { |
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73 ulongword A = (ulongword)a + (ulongword)b; |
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74 return A > MAX_LONGWORD ? MAX_LONGWORD : A; |
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75 } |
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76 } |
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77 |
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78 longword gsm_L_sub P2((a,b), longword a, longword b) |
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79 { |
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80 if (a >= 0) { |
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81 if (b >= 0) return a - b; |
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82 else { |
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83 /* a>=0, b<0 */ |
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84 |
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85 ulongword A = (ulongword)a + -(b + 1); |
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86 return A >= MAX_LONGWORD ? MAX_LONGWORD : (A + 1); |
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87 } |
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88 } |
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89 else if (b <= 0) return a - b; |
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90 else { |
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91 /* a<0, b>0 */ |
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92 |
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93 ulongword A = (ulongword)-(a + 1) + b; |
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94 return A >= MAX_LONGWORD ? MIN_LONGWORD : -(longword)A - 1; |
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95 } |
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96 } |
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97 |
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98 static unsigned char const bitoff[ 256 ] = { |
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99 8, 7, 6, 6, 5, 5, 5, 5, 4, 4, 4, 4, 4, 4, 4, 4, |
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100 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, |
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101 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, |
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102 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, |
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103 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, |
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104 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, |
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105 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, |
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106 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, |
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107 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, |
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108 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, |
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109 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, |
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110 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, |
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111 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, |
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112 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, |
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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 }; |
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116 |
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117 word gsm_norm P1((a), longword a ) |
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118 /* |
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119 * the number of left shifts needed to normalize the 32 bit |
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120 * variable L_var1 for positive values on the interval |
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121 * |
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122 * with minimum of |
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123 * minimum of 1073741824 (01000000000000000000000000000000) and |
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124 * maximum of 2147483647 (01111111111111111111111111111111) |
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125 * |
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126 * |
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127 * and for negative values on the interval with |
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128 * minimum of -2147483648 (-10000000000000000000000000000000) and |
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129 * maximum of -1073741824 ( -1000000000000000000000000000000). |
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130 * |
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131 * in order to normalize the result, the following |
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132 * operation must be done: L_norm_var1 = L_var1 << norm( L_var1 ); |
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133 * |
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134 * (That's 'ffs', only from the left, not the right..) |
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135 */ |
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136 { |
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137 assert(a != 0); |
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138 |
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139 if (a < 0) { |
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140 if (a <= -1073741824) return 0; |
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141 a = ~a; |
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142 } |
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143 |
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144 return a & 0xffff0000 |
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145 ? ( a & 0xff000000 |
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146 ? -1 + bitoff[ 0xFF & (a >> 24) ] |
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147 : 7 + bitoff[ 0xFF & (a >> 16) ] ) |
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148 : ( a & 0xff00 |
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149 ? 15 + bitoff[ 0xFF & (a >> 8) ] |
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150 : 23 + bitoff[ 0xFF & a ] ); |
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151 } |
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152 |
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153 longword gsm_L_asl P2((a,n), longword a, int n) |
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154 { |
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155 if (n >= 32) return 0; |
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156 if (n <= -32) return -(a < 0); |
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157 if (n < 0) return gsm_L_asr(a, -n); |
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158 return a << n; |
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159 } |
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160 |
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161 word gsm_asl P2((a,n), word a, int n) |
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162 { |
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163 if (n >= 16) return 0; |
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164 if (n <= -16) return -(a < 0); |
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165 if (n < 0) 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 longword gsm_L_asr P2((a,n), longword a, int n) |
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170 { |
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171 if (n >= 32) return -(a < 0); |
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172 if (n <= -32) return 0; |
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173 if (n < 0) return a << -n; |
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174 |
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175 # ifdef SASR |
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176 return a >> n; |
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177 # else |
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178 if (a >= 0) return a >> n; |
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179 else return -(longword)( -(ulongword)a >> n ); |
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180 # endif |
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181 } |
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182 |
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183 word gsm_asr P2((a,n), word a, int n) |
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184 { |
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185 if (n >= 16) return -(a < 0); |
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186 if (n <= -16) return 0; |
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187 if (n < 0) 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) return a >> n; |
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193 else return -(word)( -(uword)a >> n ); |
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194 # endif |
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195 } |
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196 |
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197 /* |
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198 * (From p. 46, end of section 4.2.5) |
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199 * |
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200 * NOTE: The following lines gives [sic] one correct implementation |
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201 * of the div(num, denum) arithmetic operation. Compute div |
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202 * which is the integer division of num by denum: with denum |
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203 * >= num > 0 |
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204 */ |
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205 |
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206 word gsm_div P2((num,denum), word num, word denum) |
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207 { |
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208 longword L_num = num; |
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209 longword L_denum = denum; |
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210 word div = 0; |
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211 int k = 15; |
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212 |
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213 /* The parameter num sometimes becomes zero. |
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214 * Although this is explicitly guarded against in 4.2.5, |
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215 * we assume that the result should then be zero as well. |
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216 */ |
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217 |
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218 /* assert(num != 0); */ |
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219 |
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220 assert(num >= 0 && denum >= num); |
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221 if (num == 0) |
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222 return 0; |
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223 |
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224 while (k--) { |
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225 div <<= 1; |
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226 L_num <<= 1; |
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227 |
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228 if (L_num >= L_denum) { |
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229 L_num -= L_denum; |
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230 div++; |
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231 } |
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232 } |
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233 |
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234 return div; |
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235 } |