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1 ------------------------------------------------------------------------------
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2 -- --
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3 -- GNAT COMPILER COMPONENTS --
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4 -- --
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5 -- T A B L E --
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6 -- --
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7 -- S p e c --
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8 -- --
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131
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9 -- Copyright (C) 1992-2018, 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 -- This package provides an implementation of dynamically resizable one
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33 -- dimensional arrays. The idea is to mimic the normal Ada semantics for
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34 -- arrays as closely as possible with the one additional capability of
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35 -- dynamically modifying the value of the Last attribute.
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36
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37 -- This package uses a very efficient memory management scheme and any
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38 -- change must be carefully evaluated on compilation of real software.
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39
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40 -- Note that this interface should remain synchronized with those in
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41 -- GNAT.Table and GNAT.Dynamic_Tables to keep coherency between these
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42 -- three related units.
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43
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44 with Types; use Types;
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45
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46 package Table is
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47 pragma Elaborate_Body;
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48
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49 generic
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50 type Table_Component_Type is private;
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51 type Table_Index_Type is range <>;
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52
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53 Table_Low_Bound : Table_Index_Type;
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54 Table_Initial : Pos;
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55 Table_Increment : Nat;
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56 Table_Name : String;
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57 Release_Threshold : Nat := 0;
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58
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59 package Table is
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60
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61 -- Table_Component_Type and Table_Index_Type specify the type of the
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62 -- array, Table_Low_Bound is the lower bound. Table_Index_Type must be
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63 -- an integer type. The effect is roughly to declare:
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64
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65 -- Table : array (Table_Index_Type range Table_Low_Bound .. <>)
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66 -- of Table_Component_Type;
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67
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68 -- Note: since the upper bound can be one less than the lower
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69 -- bound for an empty array, the table index type must be able
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70 -- to cover this range, e.g. if the lower bound is 1, then the
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71 -- Table_Index_Type should be Natural rather than Positive.
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72
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73 -- Table_Component_Type may be any Ada type, except that controlled
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74 -- types are not supported. Note however that default initialization
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75 -- will NOT occur for array components.
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76
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77 -- The Table_Initial values controls the allocation of the table when
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78 -- it is first allocated, either by default, or by an explicit Init
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79 -- call. The value used is Opt.Table_Factor * Table_Initial.
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80
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81 -- The Table_Increment value controls the amount of increase, if the
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82 -- table has to be increased in size. The value given is a percentage
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83 -- value (e.g. 100 = increase table size by 100%, i.e. double it).
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84
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85 -- The Table_Name parameter is simply use in debug output messages it
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86 -- has no other usage, and is not referenced in non-debugging mode.
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87
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88 -- The Last and Set_Last subprograms provide control over the current
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89 -- logical allocation. They are quite efficient, so they can be used
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90 -- freely (expensive reallocation occurs only at major granularity
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91 -- chunks controlled by the allocation parameters).
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92
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93 -- Note: We do not make the table components aliased, since this would
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94 -- restrict the use of table for discriminated types. If it is necessary
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95 -- to take the access of a table element, use Unrestricted_Access.
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96
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97 -- WARNING: On HPPA, the virtual addressing approach used in this unit
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98 -- is incompatible with the indexing instructions on the HPPA. So when
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99 -- using this unit, compile your application with -mdisable-indexing.
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100
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101 -- WARNING: If the table is reallocated, then the address of all its
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102 -- components will change. So do not capture the address of an element
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103 -- and then use the address later after the table may be reallocated.
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104 -- One tricky case of this is passing an element of the table to a
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105 -- subprogram by reference where the table gets reallocated during
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106 -- the execution of the subprogram. The best rule to follow is never
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107 -- to pass a table element as a parameter except for the case of IN
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108 -- mode parameters with scalar values.
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109
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110 type Table_Type is
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111 array (Table_Index_Type range <>) of Table_Component_Type;
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112
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113 subtype Big_Table_Type is
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114 Table_Type (Table_Low_Bound .. Table_Index_Type'Last);
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115 -- We work with pointers to a bogus array type that is constrained
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116 -- with the maximum possible range bound. This means that the pointer
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117 -- is a thin pointer, which is more efficient. Since subscript checks
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118 -- in any case must be on the logical, rather than physical bounds,
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119 -- safety is not compromised by this approach.
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120
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121 type Table_Ptr is access all Big_Table_Type;
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122 for Table_Ptr'Storage_Size use 0;
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123 -- The table is actually represented as a pointer to allow reallocation
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124
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125 Table : aliased Table_Ptr := null;
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126 -- The table itself. The lower bound is the value of Low_Bound.
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127 -- Logically the upper bound is the current value of Last (although
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128 -- the actual size of the allocated table may be larger than this).
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129 -- The program may only access and modify Table entries in the range
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130 -- First .. Last.
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131
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132 Locked : Boolean := False;
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133 -- Table expansion is permitted only if this switch is set to False. A
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134 -- client may set Locked to True, in which case any attempt to expand
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135 -- the table will cause an assertion failure. Note that while a table
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136 -- is locked, its address in memory remains fixed and unchanging. This
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137 -- feature is used to control table expansion during Gigi processing.
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138 -- Gigi assumes that tables other than the Uint and Ureal tables do
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139 -- not move during processing, which means that they cannot be expanded.
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140 -- The Locked flag is used to enforce this restriction.
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141
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142 procedure Init;
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143 -- This procedure allocates a new table of size Initial (freeing any
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144 -- previously allocated larger table). It is not necessary to call
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145 -- Init when a table is first instantiated (since the instantiation does
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146 -- the same initialization steps). However, it is harmless to do so, and
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147 -- Init is convenient in reestablishing a table for new use.
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148
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149 function Last return Table_Index_Type;
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150 pragma Inline (Last);
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151 -- Returns the current value of the last used entry in the table, which
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152 -- can then be used as a subscript for Table. Note that the only way to
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153 -- modify Last is to call the Set_Last procedure. Last must always be
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154 -- used to determine the logically last entry.
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155
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156 procedure Release;
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157 -- Storage is allocated in chunks according to the values given in the
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158 -- Initial and Increment parameters. If Release_Threshold is 0 or the
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159 -- length of the table does not exceed this threshold then a call to
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160 -- Release releases all storage that is allocated, but is not logically
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161 -- part of the current array value; otherwise the call to Release leaves
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162 -- the current array value plus 0.1% of the current table length free
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163 -- elements located at the end of the table (this parameter facilitates
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164 -- reopening large tables and adding a few elements without allocating a
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165 -- chunk of memory). In both cases current array values are not affected
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166 -- by this call.
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167
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168 procedure Free;
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169 -- Free all allocated memory for the table. A call to init is required
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170 -- before any use of this table after calling Free.
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171
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172 First : constant Table_Index_Type := Table_Low_Bound;
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173 -- Export First as synonym for Low_Bound (parallel with use of Last)
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174
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175 procedure Set_Last (New_Val : Table_Index_Type);
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176 pragma Inline (Set_Last);
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177 -- This procedure sets Last to the indicated value. If necessary the
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178 -- table is reallocated to accommodate the new value (i.e. on return
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179 -- the allocated table has an upper bound of at least Last). If Set_Last
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180 -- reduces the size of the table, then logically entries are removed
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181 -- from the table. If Set_Last increases the size of the table, then
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182 -- new entries are logically added to the table.
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183
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184 procedure Increment_Last;
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185 pragma Inline (Increment_Last);
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186 -- Adds 1 to Last (same as Set_Last (Last + 1)
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187
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188 procedure Decrement_Last;
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189 pragma Inline (Decrement_Last);
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190 -- Subtracts 1 from Last (same as Set_Last (Last - 1)
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191
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192 procedure Append (New_Val : Table_Component_Type);
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193 pragma Inline (Append);
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194 -- Equivalent to:
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195 -- x.Increment_Last;
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196 -- x.Table (x.Last) := New_Val;
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197 -- i.e. the table size is increased by one, and the given new item
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198 -- stored in the newly created table element.
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199
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200 procedure Append_All (New_Vals : Table_Type);
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201 -- Appends all components of New_Vals
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202
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203 procedure Set_Item
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204 (Index : Table_Index_Type;
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205 Item : Table_Component_Type);
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206 pragma Inline (Set_Item);
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207 -- Put Item in the table at position Index. The table is expanded if
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208 -- current table length is less than Index and in that case Last is set
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209 -- to Index. Item will replace any value already present in the table
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210 -- at this position.
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211
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212 type Saved_Table is private;
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213 -- Type used for Save/Restore subprograms
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214
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215 function Save return Saved_Table;
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216 -- Resets table to empty, but saves old contents of table in returned
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217 -- value, for possible later restoration by a call to Restore.
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218
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219 procedure Restore (T : Saved_Table);
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220 -- Given a Saved_Table value returned by a prior call to Save, restores
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221 -- the table to the state it was in at the time of the Save call.
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222
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223 procedure Tree_Write;
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224 -- Writes out contents of table using Tree_IO
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225
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226 procedure Tree_Read;
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227 -- Initializes table by reading contents previously written with the
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228 -- Tree_Write call (also using Tree_IO).
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229
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230 private
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231
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232 Last_Val : Int;
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233 -- Current value of Last. Note that we declare this in the private part
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234 -- because we don't want the client to modify Last except through one of
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235 -- the official interfaces (since a modification to Last may require a
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236 -- reallocation of the table).
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237
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238 Max : Int;
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239 -- Subscript of the maximum entry in the currently allocated table
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240
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241 type Saved_Table is record
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242 Last_Val : Int;
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243 Max : Int;
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244 Table : Table_Ptr;
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245 end record;
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246
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247 end Table;
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248 end Table;
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