[Pixel]<Chipndale>6.0>SafeHashTable>HashTable.mesa!1

HashTable.Mesa

Adapted from RefTab.mesa by Bertrand Serlet, July 24, 1985 4:20:46 pm PDT

Adapted from HashTable.mesa by Mike Spreitzer, October 23, 1985 5:41:07 pm PDT

Last Edited by Bertrand Serlet, July 29, 1985 11:42:28 am PDT

Last Edited by Widom, July 25, 1985 4:36:47 pm PDT

Last Edited by Mike Spreitzer, November 18, 1985 3:31:15 pm PST

Definitions for hashed REF table abstraction. Hash and Equality functions are given. Each table is monitored.

RefTab is a particular case of this interface, when defaults are used. Particular Hash and Equality functions are provided to produce behavior equivalent to SymTab.

These tables will grow in size (up to a limit), so as to keep the density (i.e., (# elements in table) / (# hash table buckets)) from growing too large. When these tables grow, they pick as new modulus a prime number at least twice as large as the old modulus. These tables will try to grow when the density exceeds 1.0 and no enumeration (Pairs) is going on.

HashTable: CEDAR DEFINITIONS = BEGIN

Table: TYPE = REF TableRec;

TableRec: PRIVATE TYPE = MONITORED RECORD [

hash: HashProc,

equal: EqualProc,

size, sizeLimit, inhibitCount: INT,

data: REF Seq

];

Seq: TYPE = PRIVATE RECORD [nodes: SEQUENCE max: SeqIndex OF Node];

Node: TYPE = PRIVATE REF NodeRep;

NodeRep: TYPE = PRIVATE RECORD [key: Key, value: Value, next: Node];

SeqIndex: TYPE = NAT;

Key: TYPE = REF;

Value: TYPE = REF;

HashProc: TYPE = PROC [Key] RETURNS [CARDINAL];

EqualProc: TYPE = PROC [Key, Key] RETURNS [BOOL];

Create: PROC [mod: SeqIndex ← 17, equal: EqualProc ← NIL, hash: HashProc ← NIL] RETURNS [Table];

creates new table, whose length is mod. The required relation between hashProc and equalProc is that 2 equal keys (equalProc returns TRUE on them) must have the same hash key. equal defaults to pointer equality, and hash defaults to a magic Xor on key adress.

RopeEqual, RopeEqualModCase: EqualProc;

Some EqualProcs that clients may find commonly useful.

HashRope, HashRopeModCase: HashProc;

Some HashProcs that clients may find commonly useful.

GetSize: PROC [table: Table] RETURNS [INT];

returns number of key-value pairs in table

Fetch: PROC [table: Table, key: Key] RETURNS [found: BOOLEAN, value: Value];

looks up key in table, returns associated value (if any)

if found is TRUE, value is value associated with given key

if found is FALSE, value is NIL

Replace: PROC [table: Table, key: Key, value: Value] RETURNS [BOOLEAN];

returns TRUE after overwriting old value for existing key-value pair

if no previous value for key, returns FALSE without inserting new pair

Store: PROC [table: Table, key: Key, value: Value] RETURNS [BOOLEAN];

returns TRUE after inserting new pair

returns FALSE after overwriting old value for existing key-value pair

Insert: PROC [table: Table, key: Key, value: Value] RETURNS [BOOLEAN];

returns TRUE after inserted new pair

if previous value existed for key, returns FALSE without changing value

Delete: PROC [table: Table, key: Key] RETURNS [BOOLEAN];

deletes key-value pair associated with given key

returns TRUE if deletion actually occurred, FALSE if no such key

Pairs: PROC [table: Table, action: EachPairAction] RETURNS [BOOLEAN];

enumerates pairs currently in symbol table in unspecified order

pairs inserted/deleted during enumeration may or may not be seen

applies action to each pair until action returns TRUE or no more pairs

returns TRUE if some action returns TRUE

EachPairAction: TYPE = PROC [key: Key, value: Value] RETURNS [quit: BOOLEAN ← FALSE];

Erase: PROC [table: Table];

deletes all key-value pairs in given table

END.