------------------------------------------------------------------------------ -- -- -- GNAT RUN-TIME COMPONENTS -- -- -- -- G N A T . D Y N A M I C _ H T A B L E S -- -- -- -- S p e c -- -- -- -- Copyright (C) 1995-2014, AdaCore -- -- -- -- GNAT is free software; you can redistribute it and/or modify it under -- -- terms of the GNU General Public License as published by the Free Soft- -- -- ware Foundation; either version 3, or (at your option) any later ver- -- -- sion. GNAT is distributed in the hope that it will be useful, but WITH- -- -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY -- -- or FITNESS FOR A PARTICULAR PURPOSE. -- -- -- -- As a special exception under Section 7 of GPL version 3, you are granted -- -- additional permissions described in the GCC Runtime Library Exception, -- -- version 3.1, as published by the Free Software Foundation. -- -- -- -- You should have received a copy of the GNU General Public License and -- -- a copy of the GCC Runtime Library Exception along with this program; -- -- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see -- -- . -- -- -- -- GNAT was originally developed by the GNAT team at New York University. -- -- Extensive contributions were provided by Ada Core Technologies Inc. -- -- -- ------------------------------------------------------------------------------ -- Hash table searching routines -- This package contains three separate packages. The Simple_HTable package -- provides a very simple abstraction that associates one element to one key -- value and takes care of all allocations automatically using the heap. The -- Static_HTable package provides a more complex interface that allows full -- control over allocation. The Load_Factor_HTable package provides a more -- complex abstraction where collisions are resolved by chaining, and the -- table grows by a percentage after the load factor has been exceeded. -- This package provides a facility similar to that of GNAT.HTable, except -- that this package declares types that can be used to define dynamic -- instances of hash tables, while instantiations in GNAT.HTable creates a -- single instance of the hash table. -- Note that this interface should remain synchronized with those in -- GNAT.HTable to keep as much coherency as possible between these two -- related units. private with Ada.Finalization; package GNAT.Dynamic_HTables is ------------------- -- Static_HTable -- ------------------- -- A low-level Hash-Table abstraction, not as easy to instantiate as -- Simple_HTable. This mirrors the interface of GNAT.HTable.Static_HTable, -- but does require dynamic allocation (since we allow multiple instances -- of the table). The model is that each Element contains its own Key that -- can be retrieved by Get_Key. Furthermore, Element provides a link that -- can be used by the HTable for linking elements with same hash codes: -- Element -- +-------------------+ -- | Key | -- +-------------------+ -- : other data : -- +-------------------+ -- | Next Elmt | -- +-------------------+ generic type Header_Num is range <>; -- An integer type indicating the number and range of hash headers type Element (<>) is limited private; -- The type of element to be stored type Elmt_Ptr is private; -- The type used to reference an element (will usually be an access -- type, but could be some other form of type such as an integer type). Null_Ptr : Elmt_Ptr; -- The null value of the Elmt_Ptr type with procedure Set_Next (E : Elmt_Ptr; Next : Elmt_Ptr); with function Next (E : Elmt_Ptr) return Elmt_Ptr; -- The type must provide an internal link for the sake of the -- staticness of the HTable. type Key is limited private; with function Get_Key (E : Elmt_Ptr) return Key; with function Hash (F : Key) return Header_Num; with function Equal (F1, F2 : Key) return Boolean; package Static_HTable is type Instance is private; Nil : constant Instance; procedure Reset (T : in out Instance); -- Resets the hash table by releasing all memory associated with -- it. The hash table can safely be reused after this call. For the -- most common case where Elmt_Ptr is an access type, and Null_Ptr is -- null, this is only needed if the same table is reused in a new -- context. If Elmt_Ptr is other than an access type, or Null_Ptr is -- other than null, then Reset must be called before the first use of -- the hash table. procedure Set (T : in out Instance; E : Elmt_Ptr); -- Insert the element pointer in the HTable function Get (T : Instance; K : Key) return Elmt_Ptr; -- Returns the latest inserted element pointer with the given Key -- or null if none. procedure Remove (T : Instance; K : Key); -- Removes the latest inserted element pointer associated with the -- given key if any, does nothing if none. function Get_First (T : Instance) return Elmt_Ptr; -- Returns Null_Ptr if the Htable is empty, otherwise returns one -- non specified element. There is no guarantee that 2 calls to this -- function will return the same element. function Get_Next (T : Instance) return Elmt_Ptr; -- Returns a non-specified element that has not been returned by the -- same function since the last call to Get_First or Null_Ptr if -- there is no such element or Get_First has never been called. If -- there is no call to 'Set' in between Get_Next calls, all the -- elements of the Htable will be traversed. private type Instance_Data; type Instance is access all Instance_Data; Nil : constant Instance := null; end Static_HTable; ------------------- -- Simple_HTable -- ------------------- -- A simple hash table abstraction, easy to instantiate, easy to use. -- The table associates one element to one key with the procedure Set. -- Get retrieves the Element stored for a given Key. The efficiency of -- retrieval is function of the size of the Table parameterized by -- Header_Num and the hashing function Hash. generic type Header_Num is range <>; -- An integer type indicating the number and range of hash headers type Element is private; -- The type of element to be stored No_Element : Element; -- The object that is returned by Get when no element has been set for -- a given key type Key is private; with function Hash (F : Key) return Header_Num; with function Equal (F1, F2 : Key) return Boolean; package Simple_HTable is type Instance is private; Nil : constant Instance; procedure Set (T : in out Instance; K : Key; E : Element); -- Associates an element with a given key. Overrides any previously -- associated element. procedure Reset (T : in out Instance); -- Releases all memory associated with the table. The table can be -- reused after this call (it is automatically allocated on the first -- access to the table). function Get (T : Instance; K : Key) return Element; -- Returns the Element associated with a key or No_Element if the -- given key has not associated element procedure Remove (T : Instance; K : Key); -- Removes the latest inserted element pointer associated with the -- given key if any, does nothing if none. function Get_First (T : Instance) return Element; -- Returns No_Element if the Htable is empty, otherwise returns one -- non specified element. There is no guarantee that two calls to this -- function will return the same element, if the Htable has been -- modified between the two calls. function Get_Next (T : Instance) return Element; -- Returns a non-specified element that has not been returned by the -- same function since the last call to Get_First or No_Element if -- there is no such element. If there is no call to 'Set' in between -- Get_Next calls, all the elements of the Htable will be traversed. -- To guarantee that all the elements of the Htable will be traversed, -- no modification of the Htable (Set, Reset, Remove) should occur -- between a call to Get_First and subsequent consecutive calls to -- Get_Next, until one of these calls returns No_Element. private type Element_Wrapper; type Elmt_Ptr is access all Element_Wrapper; type Element_Wrapper is record K : Key; E : Element; Next : Elmt_Ptr; end record; procedure Set_Next (E : Elmt_Ptr; Next : Elmt_Ptr); function Next (E : Elmt_Ptr) return Elmt_Ptr; function Get_Key (E : Elmt_Ptr) return Key; package Tab is new Static_HTable (Header_Num => Header_Num, Element => Element_Wrapper, Elmt_Ptr => Elmt_Ptr, Null_Ptr => null, Set_Next => Set_Next, Next => Next, Key => Key, Get_Key => Get_Key, Hash => Hash, Equal => Equal); type Instance is new Tab.Instance; Nil : constant Instance := Instance (Tab.Nil); end Simple_HTable; ------------------------ -- Load_Factor_HTable -- ------------------------ -- A simple hash table abstraction capable of growing once a threshold has -- been exceeded. Collisions are resolved by chaining elements onto lists -- hanging from individual buckets. This implementation does not make any -- effort to minimize the number of necessary rehashes once the table has -- been expanded, hence the term "simple". -- WARNING: This hash table implementation utilizes dynamic allocation. -- Storage reclamation is performed by the hash table. -- WARNING: This hash table implementation is not thread-safe. To achieve -- proper concurrency and synchronization, wrap an instance of a table in -- a protected object. generic type Range_Type is range <>; -- The underlying range of the hash table. Note that this type must be -- large enough to accommodate multiple expansions of the table. type Key_Type is private; type Value_Type is private; -- The types of the (key, value) pair stored in the hash table No_Value : Value_Type; -- A predefined value denoting a non-existent value Initial_Size : Positive; -- The starting size of the hash table. The hash table must contain at -- least one bucket. Growth_Percentage : Positive; -- The amount of increase expressed as a percentage. The hash table must -- grow by at least 1%. To illustrate, a value of 100 will increase the -- table by 100%, effectively doubling its size. Load_Factor : Float; -- The ratio of the elements stored within the hash table divided by the -- current size of the table. This value acts as the growth threshold. -- If exceeded, the hash table is expanded by Growth_Percentage. with function Equal (Left : Key_Type; Right : Key_Type) return Boolean; with function Hash (Key : Key_Type; Size : Positive) return Range_Type; -- Parameter Size denotes the current size of the hash table package Load_Factor_HTable is type Table is tagged limited private; function Current_Size (T : Table) return Positive; -- Obtain the current size of the table function Get (T : Table; Key : Key_Type) return Value_Type; -- Obtain the value associated with a key. This routine returns No_Value -- if the key is not present in the hash table. procedure Remove (T : in out Table; Key : Key_Type); -- Remove the value associated with the given key. This routine has no -- effect if the key is not present in the hash table. procedure Set (T : in out Table; Key : Key_Type; Val : Value_Type); -- Associate a value with a given key. This routine has no effect if the -- the (key, value) pair is already present in the hash table. Note that -- this action may cause the table to grow. private -- The following types model a bucket chain. Note that the key is also -- stored for rehashing purposes. type Element; type Element_Ptr is access all Element; type Element is record Key : Key_Type; Val : Value_Type; Prev : Element_Ptr := null; Next : Element_Ptr := null; end record; No_Element : constant Element_Ptr := null; -- The following types model the buckets of the hash table. Each bucket -- has a dummy head to facilitate insertion and deletion of elements. type Buckets_Array is array (Range_Type range <>) of aliased Element; type Buckets_Array_Ptr is access all Buckets_Array; type Table is new Ada.Finalization.Limited_Controlled with record Buckets : Buckets_Array_Ptr := null; Element_Count : Natural := 0; -- The number of (key, value) pairs stored in the hash table end record; procedure Finalize (T : in out Table); -- Destroy the contents of a hash table by reclaiming all storage used -- by buckets and their respective chains. procedure Initialize (T : in out Table); -- Create a hash table with buckets within the range Range_Type'First .. -- Range_Type'First + Initial_Size - 1. end Load_Factor_HTable; end GNAT.Dynamic_HTables;