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1 ------------------------------------------------------------------------------
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2 -- --
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3 -- GNAT RUN-TIME LIBRARY (GNARL) COMPONENTS --
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4 -- --
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5 -- S Y S T E M . B I T _ O P S --
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6 -- --
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7 -- B o d y --
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8 -- --
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131
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9 -- Copyright (C) 1996-2018, Free Software Foundation, Inc. --
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111
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10 -- --
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11 -- GNAT is free software; you can redistribute it and/or modify it under --
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12 -- terms of the GNU General Public License as published by the Free Soft- --
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13 -- ware Foundation; either version 3, or (at your option) any later ver- --
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14 -- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
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15 -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
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16 -- or FITNESS FOR A PARTICULAR PURPOSE. --
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17 -- --
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18 -- As a special exception under Section 7 of GPL version 3, you are granted --
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19 -- additional permissions described in the GCC Runtime Library Exception, --
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20 -- version 3.1, as published by the Free Software Foundation. --
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21 -- --
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22 -- You should have received a copy of the GNU General Public License and --
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23 -- a copy of the GCC Runtime Library Exception along with this program; --
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24 -- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
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25 -- <http://www.gnu.org/licenses/>. --
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26 -- --
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27 -- GNAT was originally developed by the GNAT team at New York University. --
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28 -- Extensive contributions were provided by Ada Core Technologies Inc. --
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29 -- --
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30 ------------------------------------------------------------------------------
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31
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32 pragma Compiler_Unit_Warning;
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33
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34 with System; use System;
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35 with System.Unsigned_Types; use System.Unsigned_Types;
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36
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37 with Ada.Exceptions; use Ada.Exceptions;
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38 with Ada.Unchecked_Conversion;
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39
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40 package body System.Bit_Ops is
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41
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42 subtype Bits_Array is System.Unsigned_Types.Packed_Bytes1 (Positive);
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43 -- Dummy array type used to interpret the address values. We use the
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44 -- unaligned version always, since this will handle both the aligned and
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45 -- unaligned cases, and we always do these operations by bytes anyway.
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46 -- Note: we use a ones origin array here so that the computations of the
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47 -- length in bytes work correctly (give a non-negative value) for the
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48 -- case of zero length bit strings). Note that we never allocate any
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49 -- objects of this type (we can't because they would be absurdly big).
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50
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51 type Bits is access Bits_Array;
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52 -- This is the actual type into which address values are converted
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53
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54 function To_Bits is new Ada.Unchecked_Conversion (Address, Bits);
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55
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56 LE : constant := Standard'Default_Bit_Order;
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57 -- Static constant set to 0 for big-endian, 1 for little-endian
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58
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59 -- The following is an array of masks used to mask the final byte, either
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60 -- at the high end (big-endian case) or the low end (little-endian case).
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61
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62 Masks : constant array (1 .. 7) of Packed_Byte := (
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63 (1 - LE) * 2#1000_0000# + LE * 2#0000_0001#,
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64 (1 - LE) * 2#1100_0000# + LE * 2#0000_0011#,
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65 (1 - LE) * 2#1110_0000# + LE * 2#0000_0111#,
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66 (1 - LE) * 2#1111_0000# + LE * 2#0000_1111#,
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67 (1 - LE) * 2#1111_1000# + LE * 2#0001_1111#,
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68 (1 - LE) * 2#1111_1100# + LE * 2#0011_1111#,
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69 (1 - LE) * 2#1111_1110# + LE * 2#0111_1111#);
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70
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71 -----------------------
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72 -- Local Subprograms --
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73 -----------------------
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74
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75 procedure Raise_Error;
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76 pragma No_Return (Raise_Error);
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77 -- Raise Constraint_Error, complaining about unequal lengths
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78
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79 -------------
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80 -- Bit_And --
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81 -------------
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82
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83 procedure Bit_And
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84 (Left : Address;
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85 Llen : Natural;
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86 Right : Address;
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87 Rlen : Natural;
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88 Result : Address)
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89 is
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90 LeftB : constant Bits := To_Bits (Left);
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91 RightB : constant Bits := To_Bits (Right);
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92 ResultB : constant Bits := To_Bits (Result);
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93
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94 begin
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95 if Llen /= Rlen then
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96 Raise_Error;
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97 end if;
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98
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99 for J in 1 .. (Rlen + 7) / 8 loop
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100 ResultB (J) := LeftB (J) and RightB (J);
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101 end loop;
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102 end Bit_And;
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103
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104 ------------
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105 -- Bit_Eq --
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106 ------------
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107
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108 function Bit_Eq
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109 (Left : Address;
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110 Llen : Natural;
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111 Right : Address;
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112 Rlen : Natural) return Boolean
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113 is
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114 LeftB : constant Bits := To_Bits (Left);
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115 RightB : constant Bits := To_Bits (Right);
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116
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117 begin
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118 if Llen /= Rlen then
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119 return False;
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120
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121 else
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122 declare
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123 BLen : constant Natural := Llen / 8;
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124 Bitc : constant Natural := Llen mod 8;
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125
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126 begin
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127 if LeftB (1 .. BLen) /= RightB (1 .. BLen) then
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128 return False;
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129
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130 elsif Bitc /= 0 then
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131 return
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132 ((LeftB (BLen + 1) xor RightB (BLen + 1))
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133 and Masks (Bitc)) = 0;
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134
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135 else -- Bitc = 0
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136 return True;
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137 end if;
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138 end;
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139 end if;
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140 end Bit_Eq;
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141
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142 -------------
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143 -- Bit_Not --
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144 -------------
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145
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146 procedure Bit_Not
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147 (Opnd : System.Address;
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148 Len : Natural;
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149 Result : System.Address)
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150 is
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151 OpndB : constant Bits := To_Bits (Opnd);
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152 ResultB : constant Bits := To_Bits (Result);
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153
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154 begin
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155 for J in 1 .. (Len + 7) / 8 loop
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156 ResultB (J) := not OpndB (J);
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157 end loop;
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158 end Bit_Not;
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159
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160 ------------
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161 -- Bit_Or --
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162 ------------
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163
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164 procedure Bit_Or
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165 (Left : Address;
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166 Llen : Natural;
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167 Right : Address;
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168 Rlen : Natural;
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169 Result : Address)
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170 is
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171 LeftB : constant Bits := To_Bits (Left);
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172 RightB : constant Bits := To_Bits (Right);
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173 ResultB : constant Bits := To_Bits (Result);
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174
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175 begin
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176 if Llen /= Rlen then
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177 Raise_Error;
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178 end if;
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179
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180 for J in 1 .. (Rlen + 7) / 8 loop
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181 ResultB (J) := LeftB (J) or RightB (J);
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182 end loop;
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183 end Bit_Or;
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184
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185 -------------
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186 -- Bit_Xor --
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187 -------------
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188
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189 procedure Bit_Xor
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190 (Left : Address;
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191 Llen : Natural;
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192 Right : Address;
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193 Rlen : Natural;
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194 Result : Address)
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195 is
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196 LeftB : constant Bits := To_Bits (Left);
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197 RightB : constant Bits := To_Bits (Right);
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198 ResultB : constant Bits := To_Bits (Result);
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199
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200 begin
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201 if Llen /= Rlen then
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202 Raise_Error;
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203 end if;
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204
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205 for J in 1 .. (Rlen + 7) / 8 loop
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206 ResultB (J) := LeftB (J) xor RightB (J);
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207 end loop;
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208 end Bit_Xor;
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209
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210 -----------------
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211 -- Raise_Error --
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212 -----------------
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213
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214 procedure Raise_Error is
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215 begin
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216 Raise_Exception
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217 (Constraint_Error'Identity, "operand lengths are unequal");
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218 end Raise_Error;
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219
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220 end System.Bit_Ops;
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