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1 ------------------------------------------------------------------------------
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2 -- --
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3 -- GNAT RUN-TIME COMPONENTS --
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4 -- --
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5 -- S Y S T E M . H 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) 1995-2018, AdaCore --
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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 -- Hash table searching routines
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33
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34 -- This package contains two separate packages. The Simple_HTable package
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35 -- provides a very simple abstraction that associates one element to one
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36 -- key value and takes care of all allocations automatically using the heap.
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37 -- The Static_HTable package provides a more complex interface that allows
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38 -- complete control over allocation.
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39
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40 pragma Compiler_Unit_Warning;
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41
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42 package System.HTable is
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43 pragma Preelaborate;
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44
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45 -------------------
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46 -- Simple_HTable --
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47 -------------------
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48
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49 -- A simple hash table abstraction, easy to instantiate, easy to use.
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50 -- The table associates one element to one key with the procedure Set.
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51 -- Get retrieves the Element stored for a given Key. The efficiency of
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52 -- retrieval is function of the size of the Table parameterized by
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53 -- Header_Num and the hashing function Hash.
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54
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55 generic
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56 type Header_Num is range <>;
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57 -- An integer type indicating the number and range of hash headers
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58
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59 type Element is private;
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60 -- The type of element to be stored
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61
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62 No_Element : Element;
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63 -- The object that is returned by Get when no element has been set for
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64 -- a given key.
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65
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66 type Key is private;
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67 with function Hash (F : Key) return Header_Num;
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68 with function Equal (F1, F2 : Key) return Boolean;
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69
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70 package Simple_HTable is
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71
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72 procedure Set (K : Key; E : Element);
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73 -- Associates an element with a given key. Overrides any previously
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74 -- associated element.
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75
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76 procedure Reset;
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77 -- Removes and frees all elements in the table
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78
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79 function Get (K : Key) return Element;
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80 -- Returns the Element associated with a key or No_Element if the
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81 -- given key has no associated element.
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82
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83 procedure Remove (K : Key);
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84 -- Removes the latest inserted element pointer associated with the
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85 -- given key if any, does nothing if none.
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86
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87 function Get_First return Element;
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88 -- Returns No_Element if the HTable is empty, otherwise returns one
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89 -- non specified element. There is no guarantee that two calls to this
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90 -- function will return the same element.
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91
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92 function Get_Next return Element;
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93 -- Returns a non-specified element that has not been returned by the
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94 -- same function since the last call to Get_First or No_Element if
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95 -- there is no such element. If there is no call to Set in between
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96 -- Get_Next calls, all the elements of the HTable will be traversed.
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97
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98 procedure Get_First (K : in out Key; E : out Element);
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99 -- This version of the iterator returns a key/element pair. A non-
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100 -- specified entry is returned, and there is no guarantee that two
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101 -- calls to this procedure will return the same element. If the table
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102 -- is empty, E is set to No_Element, and K is unchanged, otherwise
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103 -- K and E are set to the first returned entry.
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104
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105 procedure Get_Next (K : in out Key; E : out Element);
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106 -- This version of the iterator returns a key/element pair. It returns
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107 -- a non-specified element that has not been returned since the last
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108 -- call to Get_First. If there is no remaining element, then E is set
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109 -- to No_Element, and the value in K is unchanged, otherwise K and E
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110 -- are set to the next entry. If there is no call to Set in between
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111 -- Get_Next calls, all the elements of the HTable will be traversed.
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112
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113 end Simple_HTable;
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114
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115 -------------------
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116 -- Static_HTable --
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117 -------------------
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118
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119 -- A low-level Hash-Table abstraction, not as easy to instantiate as
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120 -- Simple_HTable but designed to allow complete control over the
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121 -- allocation of necessary data structures. Particularly useful when
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122 -- dynamic allocation is not desired. The model is that each Element
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123 -- contains its own Key that can be retrieved by Get_Key. Furthermore,
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124 -- Element provides a link that can be used by the HTable for linking
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125 -- elements with same hash codes:
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126
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127 -- Element
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128
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129 -- +-------------------+
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130 -- | Key |
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131 -- +-------------------+
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132 -- : other data :
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133 -- +-------------------+
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134 -- | Next Elmt |
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135 -- +-------------------+
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136
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137 generic
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138 type Header_Num is range <>;
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139 -- An integer type indicating the number and range of hash headers
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140
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141 type Element (<>) is limited private;
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142 -- The type of element to be stored. This is historically part of the
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143 -- interface, even though it is not used at all in the operations of
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144 -- the package.
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145
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146 pragma Warnings (Off, Element);
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147 -- We have to kill warnings here, because Element is and always
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148 -- has been unreferenced, but we cannot remove it at this stage,
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149 -- since this unit is in wide use, and it certainly seems harmless.
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150
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151 type Elmt_Ptr is private;
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152 -- The type used to reference an element (will usually be an access
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153 -- type, but could be some other form of type such as an integer type).
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154
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155 Null_Ptr : Elmt_Ptr;
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156 -- The null value of the Elmt_Ptr type
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157
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158 with procedure Set_Next (E : Elmt_Ptr; Next : Elmt_Ptr);
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159 with function Next (E : Elmt_Ptr) return Elmt_Ptr;
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160 -- The type must provide an internal link for the sake of the
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161 -- staticness of the HTable.
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162
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163 type Key is limited private;
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164 with function Get_Key (E : Elmt_Ptr) return Key;
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165 with function Hash (F : Key) return Header_Num;
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166 with function Equal (F1, F2 : Key) return Boolean;
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167
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168 package Static_HTable is
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169
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170 procedure Reset;
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171 -- Resets the hash table by setting all its elements to Null_Ptr. The
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172 -- effect is to clear the hash table so that it can be reused. For the
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173 -- most common case where Elmt_Ptr is an access type, and Null_Ptr is
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174 -- null, this is only needed if the same table is reused in a new
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175 -- context. If Elmt_Ptr is other than an access type, or Null_Ptr is
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176 -- other than null, then Reset must be called before the first use
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177 -- of the hash table.
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178
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179 procedure Set (E : Elmt_Ptr);
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180 -- Insert the element pointer in the HTable
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181
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182 function Get (K : Key) return Elmt_Ptr;
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183 -- Returns the latest inserted element pointer with the given Key
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184 -- or null if none.
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185
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186 function Present (K : Key) return Boolean;
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187 -- True if an element whose Get_Key is K is in the table
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188
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189 function Set_If_Not_Present (E : Elmt_Ptr) return Boolean;
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190 -- If Present (Get_Key (E)), returns False. Otherwise, does Set (E), and
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191 -- then returns True. Present (Get_Key (E)) is always True afterward,
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192 -- and the result True indicates E is newly Set.
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193
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194 procedure Remove (K : Key);
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195 -- Removes the latest inserted element pointer associated with the
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196 -- given key if any, does nothing if none.
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197
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198 function Get_First return Elmt_Ptr;
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199 -- Returns Null_Ptr if the HTable is empty, otherwise returns one
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200 -- non specified element. There is no guarantee that two calls to this
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201 -- function will return the same element.
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202
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203 function Get_Next return Elmt_Ptr;
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204 -- Returns a non-specified element that has not been returned by the
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205 -- same function since the last call to Get_First or Null_Ptr if
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206 -- there is no such element or Get_First has never been called. If
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207 -- there is no call to 'Set' in between Get_Next calls, all the
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208 -- elements of the HTable will be traversed.
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209
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210 end Static_HTable;
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211
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212 ----------
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213 -- Hash --
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214 ----------
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215
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216 -- A generic hashing function working on String keys
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217
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218 generic
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219 type Header_Num is range <>;
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220 function Hash (Key : String) return Header_Num;
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221
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222 end System.HTable;
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