gcc/ada/g-dynhta.ads

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                         GNAT RUN-TIME COMPONENTS                         --
   4 --                                                                          --
   5 --                 G N A T . D Y N A M I C _ H T A B L E S                  --
   6 --                                                                          --
   7 --                                 S p e c                                  --
   8 --                                                                          --
   9 --                     Copyright (C) 1995-2014, AdaCore                     --
  10 --                                                                          --
  11 -- GNAT is free software;  you can  redistribute it  and/or modify it under --
  12 -- terms of the  GNU General Public License as published  by the Free Soft- --
  13 -- ware  Foundation;  either version 3,  or (at your option) any later ver- --
  14 -- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
  15 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  16 -- or FITNESS FOR A PARTICULAR PURPOSE.                                     --
  17 --                                                                          --
  18 -- As a special exception under Section 7 of GPL version 3, you are granted --
  19 -- additional permissions described in the GCC Runtime Library Exception,   --
  20 -- version 3.1, as published by the Free Software Foundation.               --
  21 --                                                                          --
  22 -- You should have received a copy of the GNU General Public License and    --
  23 -- a copy of the GCC Runtime Library Exception along with this program;     --
  24 -- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
  25 -- <http://www.gnu.org/licenses/>.                                          --
  26 --                                                                          --
  27 -- GNAT was originally developed  by the GNAT team at  New York University. --
  28 -- Extensive contributions were provided by Ada Core Technologies Inc.      --
  29 --                                                                          --
  30 ------------------------------------------------------------------------------
  31
  32 --  Hash table searching routines
  33
  34 --  This package contains three separate packages. The Simple_HTable package
  35 --  provides a very simple abstraction that associates one element to one key
  36 --  value and takes care of all allocations automatically using the heap. The
  37 --  Static_HTable package provides a more complex interface that allows full
  38 --  control over allocation. The Load_Factor_HTable package provides a more
  39 --  complex abstraction where collisions are resolved by chaining, and the
  40 --  table grows by a percentage after the load factor has been exceeded.
  41
  42 --  This package provides a facility similar to that of GNAT.HTable, except
  43 --  that this package declares types that can be used to define dynamic
  44 --  instances of hash tables, while instantiations in GNAT.HTable creates a
  45 --  single instance of the hash table.
  46
  47 --  Note that this interface should remain synchronized with those in
  48 --  GNAT.HTable to keep as much coherency as possible between these two
  49 --  related units.
  50
  51 private with Ada.Finalization;
  52
  53 package GNAT.Dynamic_HTables is
  54
  55    -------------------
  56    -- Static_HTable --
  57    -------------------
  58
  59    --  A low-level Hash-Table abstraction, not as easy to instantiate as
  60    --  Simple_HTable. This mirrors the interface of GNAT.HTable.Static_HTable,
  61    --  but does require dynamic allocation (since we allow multiple instances
  62    --  of the table). The model is that each Element contains its own Key that
  63    --  can be retrieved by Get_Key. Furthermore, Element provides a link that
  64    --  can be used by the HTable for linking elements with same hash codes:
  65
  66    --       Element
  67
  68    --         +-------------------+
  69    --         |       Key         |
  70    --         +-------------------+
  71    --         :    other data     :
  72    --         +-------------------+
  73    --         |     Next Elmt     |
  74    --         +-------------------+
  75
  76    generic
  77       type Header_Num is range <>;
  78       --  An integer type indicating the number and range of hash headers
  79
  80       type Element (<>) is limited private;
  81       --  The type of element to be stored
  82
  83       type Elmt_Ptr is private;
  84       --  The type used to reference an element (will usually be an access
  85       --  type, but could be some other form of type such as an integer type).
  86
  87       Null_Ptr : Elmt_Ptr;
  88       --  The null value of the Elmt_Ptr type
  89
  90       with procedure Set_Next (E : Elmt_Ptr; Next : Elmt_Ptr);
  91       with function  Next     (E : Elmt_Ptr) return Elmt_Ptr;
  92       --  The type must provide an internal link for the sake of the
  93       --  staticness of the HTable.
  94
  95       type Key is limited private;
  96       with function Get_Key (E : Elmt_Ptr) return Key;
  97       with function Hash    (F : Key)      return Header_Num;
  98       with function Equal   (F1, F2 : Key) return Boolean;
  99
 100    package Static_HTable is
 101
 102       type Instance is private;
 103       Nil : constant Instance;
 104
 105       procedure Reset (T : in out Instance);
 106       --  Resets the hash table by releasing all memory associated with
 107       --  it. The hash table can safely be reused after this call. For the
 108       --  most common case where Elmt_Ptr is an access type, and Null_Ptr is
 109       --  null, this is only needed if the same table is reused in a new
 110       --  context. If Elmt_Ptr is other than an access type, or Null_Ptr is
 111       --  other than null, then Reset must be called before the first use of
 112       --  the hash table.
 113
 114       procedure Set (T : in out Instance; E : Elmt_Ptr);
 115       --  Insert the element pointer in the HTable
 116
 117       function Get (T : Instance; K : Key) return Elmt_Ptr;
 118       --  Returns the latest inserted element pointer with the given Key
 119       --  or null if none.
 120
 121       procedure Remove (T : Instance; K : Key);
 122       --  Removes the latest inserted element pointer associated with the
 123       --  given key if any, does nothing if none.
 124
 125       function Get_First (T : Instance) return Elmt_Ptr;
 126       --  Returns Null_Ptr if the Htable is empty, otherwise returns one
 127       --  non specified element. There is no guarantee that 2 calls to this
 128       --  function will return the same element.
 129
 130       function Get_Next (T : Instance) return Elmt_Ptr;
 131       --  Returns a non-specified element that has not been returned by the
 132       --  same function since the last call to Get_First or Null_Ptr if
 133       --  there is no such element or Get_First has never been called. If
 134       --  there is no call to 'Set' in between Get_Next calls, all the
 135       --  elements of the Htable will be traversed.
 136
 137    private
 138       type Instance_Data;
 139       type Instance is access all Instance_Data;
 140       Nil : constant Instance := null;
 141    end Static_HTable;
 142
 143    -------------------
 144    -- Simple_HTable --
 145    -------------------
 146
 147    --  A simple hash table abstraction, easy to instantiate, easy to use.
 148    --  The table associates one element to one key with the procedure Set.
 149    --  Get retrieves the Element stored for a given Key. The efficiency of
 150    --  retrieval is function of the size of the Table parameterized by
 151    --  Header_Num and the hashing function Hash.
 152
 153    generic
 154       type Header_Num is range <>;
 155       --  An integer type indicating the number and range of hash headers
 156
 157       type Element is private;
 158       --  The type of element to be stored
 159
 160       No_Element : Element;
 161       --  The object that is returned by Get when no element has been set for
 162       --  a given key
 163
 164       type Key is private;
 165       with function Hash  (F : Key)      return Header_Num;
 166       with function Equal (F1, F2 : Key) return Boolean;
 167
 168    package Simple_HTable is
 169
 170       type Instance is private;
 171       Nil : constant Instance;
 172
 173       procedure Set (T : in out Instance; K : Key; E : Element);
 174       --  Associates an element with a given key. Overrides any previously
 175       --  associated element.
 176
 177       procedure Reset (T : in out Instance);
 178       --  Releases all memory associated with the table. The table can be
 179       --  reused after this call (it is automatically allocated on the first
 180       --  access to the table).
 181
 182       function Get (T : Instance; K : Key) return Element;
 183       --  Returns the Element associated with a key or No_Element if the
 184       --  given key has not associated element
 185
 186       procedure Remove (T : Instance; K : Key);
 187       --  Removes the latest inserted element pointer associated with the
 188       --  given key if any, does nothing if none.
 189
 190       function Get_First (T : Instance) return Element;
 191       --  Returns No_Element if the Htable is empty, otherwise returns one
 192       --  non specified element. There is no guarantee that two calls to this
 193       --  function will return the same element, if the Htable has been
 194       --  modified between the two calls.
 195
 196       function Get_Next (T : Instance) return Element;
 197       --  Returns a non-specified element that has not been returned by the
 198       --  same function since the last call to Get_First or No_Element if
 199       --  there is no such element. If there is no call to 'Set' in between
 200       --  Get_Next calls, all the elements of the Htable will be traversed.
 201       --  To guarantee that all the elements of the Htable will be traversed,
 202       --  no modification of the Htable (Set, Reset, Remove) should occur
 203       --  between a call to Get_First and subsequent consecutive calls to
 204       --  Get_Next, until one of these calls returns No_Element.
 205
 206    private
 207
 208       type Element_Wrapper;
 209       type Elmt_Ptr is access all Element_Wrapper;
 210       type Element_Wrapper is record
 211          K    : Key;
 212          E    : Element;
 213          Next : Elmt_Ptr;
 214       end record;
 215
 216       procedure Set_Next (E : Elmt_Ptr; Next : Elmt_Ptr);
 217       function  Next     (E : Elmt_Ptr) return Elmt_Ptr;
 218       function  Get_Key  (E : Elmt_Ptr) return Key;
 219
 220       package Tab is new Static_HTable
 221         (Header_Num => Header_Num,
 222          Element    => Element_Wrapper,
 223          Elmt_Ptr   => Elmt_Ptr,
 224          Null_Ptr   => null,
 225          Set_Next   => Set_Next,
 226          Next       => Next,
 227          Key        => Key,
 228          Get_Key    => Get_Key,
 229          Hash       => Hash,
 230          Equal      => Equal);
 231
 232       type Instance is new Tab.Instance;
 233       Nil : constant Instance := Instance (Tab.Nil);
 234
 235    end Simple_HTable;
 236
 237    ------------------------
 238    -- Load_Factor_HTable --
 239    ------------------------
 240
 241    --  A simple hash table abstraction capable of growing once a threshold has
 242    --  been exceeded. Collisions are resolved by chaining elements onto lists
 243    --  hanging from individual buckets. This implementation does not make any
 244    --  effort to minimize the number of necessary rehashes once the table has
 245    --  been expanded, hence the term "simple".
 246
 247    --  WARNING: This hash table implementation utilizes dynamic allocation.
 248    --  Storage reclamation is performed by the hash table.
 249
 250    --  WARNING: This hash table implementation is not thread-safe. To achieve
 251    --  proper concurrency and synchronization, wrap an instance of a table in
 252    --  a protected object.
 253
 254    generic
 255       type Range_Type is range <>;
 256       --  The underlying range of the hash table. Note that this type must be
 257       --  large enough to accommodate multiple expansions of the table.
 258
 259       type Key_Type is private;
 260       type Value_Type is private;
 261       --  The types of the (key, value) pair stored in the hash table
 262
 263       No_Value : Value_Type;
 264       --  A predefined value denoting a non-existent value
 265
 266       Initial_Size : Positive;
 267       --  The starting size of the hash table. The hash table must contain at
 268       --  least one bucket.
 269
 270       Growth_Percentage : Positive;
 271       --  The amount of increase expressed as a percentage. The hash table must
 272       --  grow by at least 1%. To illustrate, a value of 100 will increase the
 273       --  table by 100%, effectively doubling its size.
 274
 275       Load_Factor : Float;
 276       --  The ratio of the elements stored within the hash table divided by the
 277       --  current size of the table. This value acts as the growth threshold.
 278       --  If exceeded, the hash table is expanded by Growth_Percentage.
 279
 280       with function Equal
 281         (Left  : Key_Type;
 282          Right : Key_Type) return Boolean;
 283
 284       with function Hash
 285         (Key  : Key_Type;
 286          Size : Positive) return Range_Type;
 287       --  Parameter Size denotes the current size of the hash table
 288
 289    package Load_Factor_HTable is
 290       type Table is tagged limited private;
 291
 292       function Current_Size (T : Table) return Positive;
 293       --  Obtain the current size of the table
 294
 295       function Get (T : Table; Key : Key_Type) return Value_Type;
 296       --  Obtain the value associated with a key. This routine returns No_Value
 297       --  if the key is not present in the hash table.
 298
 299       procedure Remove (T : in out Table; Key : Key_Type);
 300       --  Remove the value associated with the given key. This routine has no
 301       --  effect if the key is not present in the hash table.
 302
 303       procedure Set
 304         (T   : in out Table;
 305          Key : Key_Type;
 306          Val : Value_Type);
 307       --  Associate a value with a given key. This routine has no effect if the
 308       --  the (key, value) pair is already present in the hash table. Note that
 309       --  this action may cause the table to grow.
 310
 311    private
 312       --  The following types model a bucket chain. Note that the key is also
 313       --  stored for rehashing purposes.
 314
 315       type Element;
 316       type Element_Ptr is access all Element;
 317       type Element is record
 318          Key  : Key_Type;
 319          Val  : Value_Type;
 320          Prev : Element_Ptr := null;
 321          Next : Element_Ptr := null;
 322       end record;
 323
 324       No_Element : constant Element_Ptr := null;
 325
 326       --  The following types model the buckets of the hash table. Each bucket
 327       --  has a dummy head to facilitate insertion and deletion of elements.
 328
 329       type Buckets_Array is array (Range_Type range <>) of aliased Element;
 330       type Buckets_Array_Ptr is access all Buckets_Array;
 331
 332       type Table is new Ada.Finalization.Limited_Controlled with record
 333          Buckets : Buckets_Array_Ptr := null;
 334
 335          Element_Count : Natural := 0;
 336          --  The number of (key, value) pairs stored in the hash table
 337       end record;
 338
 339       procedure Finalize (T : in out Table);
 340       --  Destroy the contents of a hash table by reclaiming all storage used
 341       --  by buckets and their respective chains.
 342
 343       procedure Initialize (T : in out Table);
 344       --  Create a hash table with buckets within the range Range_Type'First ..
 345       --  Range_Type'First + Initial_Size - 1.
 346
 347    end Load_Factor_HTable;
 348
 349 end GNAT.Dynamic_HTables;