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/* -*- Mode: C; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
/* ***** BEGIN LICENSE BLOCK *****
* Version: MPL 1.1/GPL 2.0/LGPL 2.1
*
* The contents of this file are subject to the Mozilla Public License Version
* 1.1 (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
* http://www.mozilla.org/MPL/
*
* Software distributed under the License is distributed on an "AS IS" basis,
* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
* for the specific language governing rights and limitations under the
* License.
*
* The Original Code is Mozilla JavaScript code.
*
* The Initial Developer of the Original Code is
* Netscape Communications Corporation.
* Portions created by the Initial Developer are Copyright (C) 1999-2001
* the Initial Developer. All Rights Reserved.
*
* Contributor(s):
* Brendan Eich <brendan@mozilla.org> (Original Author)
*
* Alternatively, the contents of this file may be used under the terms of
* either of the GNU General Public License Version 2 or later (the "GPL"),
* or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
* in which case the provisions of the GPL or the LGPL are applicable instead
* of those above. If you wish to allow use of your version of this file only
* under the terms of either the GPL or the LGPL, and not to allow others to
* use your version of this file under the terms of the MPL, indicate your
* decision by deleting the provisions above and replace them with the notice
* and other provisions required by the GPL or the LGPL. If you do not delete
* the provisions above, a recipient may use your version of this file under
* the terms of any one of the MPL, the GPL or the LGPL.
*
* ***** END LICENSE BLOCK ***** */
#ifndef pldhash_h___
#define pldhash_h___
/*
* Double hashing, a la Knuth 6.
* GENERATED BY js/src/plify_jsdhash.sed -- DO NOT EDIT!!!
*/
#include "nscore.h"
PR_BEGIN_EXTERN_C
#if defined(__GNUC__) && defined(__i386__) && (__GNUC__ >= 3) && !defined(XP_OS2)
#define PL_DHASH_FASTCALL __attribute__ ((regparm (3),stdcall))
#elif defined(XP_WIN)
#define PL_DHASH_FASTCALL __fastcall
#else
#define PL_DHASH_FASTCALL
#endif
#ifdef DEBUG_XXXbrendan
#define PL_DHASHMETER 1
#endif
/* Table size limit, do not equal or exceed (see min&maxAlphaFrac, below). */
#undef PL_DHASH_SIZE_LIMIT
#define PL_DHASH_SIZE_LIMIT PR_BIT(24)
/* Minimum table size, or gross entry count (net is at most .75 loaded). */
#ifndef PL_DHASH_MIN_SIZE
#define PL_DHASH_MIN_SIZE 16
#elif (PL_DHASH_MIN_SIZE & (PL_DHASH_MIN_SIZE - 1)) != 0
#error "PL_DHASH_MIN_SIZE must be a power of two!"
#endif
/*
* Multiplicative hash uses an unsigned 32 bit integer and the golden ratio,
* expressed as a fixed-point 32-bit fraction.
*/
#define PL_DHASH_BITS 32
#define PL_DHASH_GOLDEN_RATIO 0x9E3779B9U
/* Primitive and forward-struct typedefs. */
typedef PRUint32 PLDHashNumber;
typedef struct PLDHashEntryHdr PLDHashEntryHdr;
typedef struct PLDHashEntryStub PLDHashEntryStub;
typedef struct PLDHashTable PLDHashTable;
typedef struct PLDHashTableOps PLDHashTableOps;
/*
* Table entry header structure.
*
* In order to allow in-line allocation of key and value, we do not declare
* either here. Instead, the API uses const void *key as a formal parameter,
* and asks each entry for its key when necessary via a getKey callback, used
* when growing or shrinking the table. Other callback types are defined
* below and grouped into the PLDHashTableOps structure, for single static
* initialization per hash table sub-type.
*
* Each hash table sub-type should nest the PLDHashEntryHdr structure at the
* front of its particular entry type. The keyHash member contains the result
* of multiplying the hash code returned from the hashKey callback (see below)
* by PL_DHASH_GOLDEN_RATIO, then constraining the result to avoid the magic 0
* and 1 values. The stored keyHash value is table size invariant, and it is
* maintained automatically by PL_DHashTableOperate -- users should never set
* it, and its only uses should be via the entry macros below.
*
* The PL_DHASH_ENTRY_IS_LIVE macro tests whether entry is neither free nor
* removed. An entry may be either busy or free; if busy, it may be live or
* removed. Consumers of this API should not access members of entries that
* are not live.
*
* However, use PL_DHASH_ENTRY_IS_BUSY for faster liveness testing of entries
* returned by PL_DHashTableOperate, as PL_DHashTableOperate never returns a
* non-live, busy (i.e., removed) entry pointer to its caller. See below for
* more details on PL_DHashTableOperate's calling rules.
*/
struct PLDHashEntryHdr {
PLDHashNumber keyHash; /* every entry must begin like this */
};
#define PL_DHASH_ENTRY_IS_FREE(entry) ((entry)->keyHash == 0)
#define PL_DHASH_ENTRY_IS_BUSY(entry) (!PL_DHASH_ENTRY_IS_FREE(entry))
#define PL_DHASH_ENTRY_IS_LIVE(entry) ((entry)->keyHash >= 2)
/*
* A PLDHashTable is currently 8 words (without the PL_DHASHMETER overhead)
* on most architectures, and may be allocated on the stack or within another
* structure or class (see below for the Init and Finish functions to use).
*
* To decide whether to use double hashing vs. chaining, we need to develop a
* trade-off relation, as follows:
*
* Let alpha be the load factor, esize the entry size in words, count the
* entry count, and pow2 the power-of-two table size in entries.
*
* (PLDHashTable overhead) > (PLHashTable overhead)
* (unused table entry space) > (malloc and .next overhead per entry) +
* (buckets overhead)
* (1 - alpha) * esize * pow2 > 2 * count + pow2
*
* Notice that alpha is by definition (count / pow2):
*
* (1 - alpha) * esize * pow2 > 2 * alpha * pow2 + pow2
* (1 - alpha) * esize > 2 * alpha + 1
*
* esize > (1 + 2 * alpha) / (1 - alpha)
*
* This assumes both tables must keep keyHash, key, and value for each entry,
* where key and value point to separately allocated strings or structures.
* If key and value can be combined into one pointer, then the trade-off is:
*
* esize > (1 + 3 * alpha) / (1 - alpha)
*
* If the entry value can be a subtype of PLDHashEntryHdr, rather than a type
* that must be allocated separately and referenced by an entry.value pointer
* member, and provided key's allocation can be fused with its entry's, then
* k (the words wasted per entry with chaining) is 4.
*
* To see these curves, feed gnuplot input like so:
*
* gnuplot> f(x,k) = (1 + k * x) / (1 - x)
* gnuplot> plot [0:.75] f(x,2), f(x,3), f(x,4)
*
* For k of 2 and a well-loaded table (alpha > .5), esize must be more than 4
* words for chaining to be more space-efficient than double hashing.
*
* Solving for alpha helps us decide when to shrink an underloaded table:
*
* esize > (1 + k * alpha) / (1 - alpha)
* esize - alpha * esize > 1 + k * alpha
* esize - 1 > (k + esize) * alpha
* (esize - 1) / (k + esize) > alpha
*
* alpha < (esize - 1) / (esize + k)
*
* Therefore double hashing should keep alpha >= (esize - 1) / (esize + k),
* assuming esize is not too large (in which case, chaining should probably be
* used for any alpha). For esize=2 and k=3, we want alpha >= .2; for esize=3
* and k=2, we want alpha >= .4. For k=4, esize could be 6, and alpha >= .5
* would still obtain. See the PL_DHASH_MIN_ALPHA macro further below.
*
* The current implementation uses a configurable lower bound on alpha, which
* defaults to .25, when deciding to shrink the table (while still respecting
* PL_DHASH_MIN_SIZE).
*
* Note a qualitative difference between chaining and double hashing: under
* chaining, entry addresses are stable across table shrinks and grows. With
* double hashing, you can't safely hold an entry pointer and use it after an
* ADD or REMOVE operation, unless you sample table->generation before adding
* or removing, and compare the sample after, dereferencing the entry pointer
* only if table->generation has not changed.
*
* The moral of this story: there is no one-size-fits-all hash table scheme,
* but for small table entry size, and assuming entry address stability is not
* required, double hashing wins.
*/
struct PLDHashTable {
const PLDHashTableOps *ops; /* virtual operations, see below */
void *data; /* ops- and instance-specific data */
PRInt16 hashShift; /* multiplicative hash shift */
uint8 maxAlphaFrac; /* 8-bit fixed point max alpha */
uint8 minAlphaFrac; /* 8-bit fixed point min alpha */
PRUint32 entrySize; /* number of bytes in an entry */
PRUint32 entryCount; /* number of entries in table */
PRUint32 removedCount; /* removed entry sentinels in table */
PRUint32 generation; /* entry storage generation number */
char *entryStore; /* entry storage */
#ifdef PL_DHASHMETER
struct PLDHashStats {
PRUint32 searches; /* total number of table searches */
PRUint32 steps; /* hash chain links traversed */
PRUint32 hits; /* searches that found key */
PRUint32 misses; /* searches that didn't find key */
PRUint32 lookups; /* number of PL_DHASH_LOOKUPs */
PRUint32 addMisses; /* adds that miss, and do work */
PRUint32 addOverRemoved; /* adds that recycled a removed entry */
PRUint32 addHits; /* adds that hit an existing entry */
PRUint32 addFailures; /* out-of-memory during add growth */
PRUint32 removeHits; /* removes that hit, and do work */
PRUint32 removeMisses; /* useless removes that miss */
PRUint32 removeFrees; /* removes that freed entry directly */
PRUint32 removeEnums; /* removes done by Enumerate */
PRUint32 grows; /* table expansions */
PRUint32 shrinks; /* table contractions */
PRUint32 compresses; /* table compressions */
PRUint32 enumShrinks; /* contractions after Enumerate */
} stats;
#endif
};
/*
* Size in entries (gross, not net of free and removed sentinels) for table.
* We store hashShift rather than sizeLog2 to optimize the collision-free case
* in SearchTable.
*/
#define PL_DHASH_TABLE_SIZE(table) PR_BIT(PL_DHASH_BITS - (table)->hashShift)
/*
* Table space at entryStore is allocated and freed using these callbacks.
* The allocator should return null on error only (not if called with nbytes
* equal to 0; but note that pldhash.c code will never call with 0 nbytes).
*/
typedef void *
(* PR_CALLBACK PLDHashAllocTable)(PLDHashTable *table, PRUint32 nbytes);
typedef void
(* PR_CALLBACK PLDHashFreeTable) (PLDHashTable *table, void *ptr);
/*
* When a table grows or shrinks, each entry is queried for its key using this
* callback. NB: in that event, entry is not in table any longer; it's in the
* old entryStore vector, which is due to be freed once all entries have been
* moved via moveEntry callbacks.
*/
typedef const void *
(* PR_CALLBACK PLDHashGetKey) (PLDHashTable *table,
PLDHashEntryHdr *entry);
/*
* Compute the hash code for a given key to be looked up, added, or removed
* from table. A hash code may have any PLDHashNumber value.
*/
typedef PLDHashNumber
(* PR_CALLBACK PLDHashHashKey) (PLDHashTable *table, const void *key);
/*
* Compare the key identifying entry in table with the provided key parameter.
* Return PR_TRUE if keys match, PR_FALSE otherwise.
*/
typedef PRBool
(* PR_CALLBACK PLDHashMatchEntry)(PLDHashTable *table,
const PLDHashEntryHdr *entry,
const void *key);
/*
* Copy the data starting at from to the new entry storage at to. Do not add
* reference counts for any strong references in the entry, however, as this
* is a "move" operation: the old entry storage at from will be freed without
* any reference-decrementing callback shortly.
*/
typedef void
(* PR_CALLBACK PLDHashMoveEntry)(PLDHashTable *table,
const PLDHashEntryHdr *from,
PLDHashEntryHdr *to);
/*
* Clear the entry and drop any strong references it holds. This callback is
* invoked during a PL_DHASH_REMOVE operation (see below for operation codes),
* but only if the given key is found in the table.
*/
typedef void
(* PR_CALLBACK PLDHashClearEntry)(PLDHashTable *table,
PLDHashEntryHdr *entry);
/*
* Called when a table (whether allocated dynamically by itself, or nested in
* a larger structure, or allocated on the stack) is finished. This callback
* allows table->ops-specific code to finalize table->data.
*/
typedef void
(* PR_CALLBACK PLDHashFinalize) (PLDHashTable *table);
/*
* Initialize a new entry, apart from keyHash. This function is called when
* PL_DHashTableOperate's PL_DHASH_ADD case finds no existing entry for the
* given key, and must add a new one. At that point, entry->keyHash is not
* set yet, to avoid claiming the last free entry in a severely overloaded
* table.
*/
typedef PRBool
(* PR_CALLBACK PLDHashInitEntry)(PLDHashTable *table,
PLDHashEntryHdr *entry,
const void *key);
/*
* Finally, the "vtable" structure for PLDHashTable. The first eight hooks
* must be provided by implementations; they're called unconditionally by the
* generic pldhash.c code. Hooks after these may be null.
*
* Summary of allocation-related hook usage with C++ placement new emphasis:
* allocTable Allocate raw bytes with malloc, no ctors run.
* freeTable Free raw bytes with free, no dtors run.
* initEntry Call placement new using default key-based ctor.
* Return PR_TRUE on success, PR_FALSE on error.
* moveEntry Call placement new using copy ctor, run dtor on old
* entry storage.
* clearEntry Run dtor on entry.
* finalize Stub unless table->data was initialized and needs to
* be finalized.
*
* Note the reason why initEntry is optional: the default hooks (stubs) clear
* entry storage: On successful PL_DHashTableOperate(tbl, key, PL_DHASH_ADD),
* the returned entry pointer addresses an entry struct whose keyHash member
* has been set non-zero, but all other entry members are still clear (null).
* PL_DHASH_ADD callers can test such members to see whether the entry was
* newly created by the PL_DHASH_ADD call that just succeeded. If placement
* new or similar initialization is required, define an initEntry hook. Of
* course, the clearEntry hook must zero or null appropriately.
*
* XXX assumes 0 is null for pointer types.
*/
struct PLDHashTableOps {
/* Mandatory hooks. All implementations must provide these. */
PLDHashAllocTable allocTable;
PLDHashFreeTable freeTable;
PLDHashGetKey getKey;
PLDHashHashKey hashKey;
PLDHashMatchEntry matchEntry;
PLDHashMoveEntry moveEntry;
PLDHashClearEntry clearEntry;
PLDHashFinalize finalize;
/* Optional hooks start here. If null, these are not called. */
PLDHashInitEntry initEntry;
};
/*
* Default implementations for the above ops.
*/
NS_COM_GLUE void *
PL_DHashAllocTable(PLDHashTable *table, PRUint32 nbytes);
NS_COM_GLUE void
PL_DHashFreeTable(PLDHashTable *table, void *ptr);
NS_COM_GLUE PLDHashNumber
PL_DHashStringKey(PLDHashTable *table, const void *key);
/* A minimal entry contains a keyHash header and a void key pointer. */
struct PLDHashEntryStub {
PLDHashEntryHdr hdr;
const void *key;
};
NS_COM_GLUE const void *
PL_DHashGetKeyStub(PLDHashTable *table, PLDHashEntryHdr *entry);
NS_COM_GLUE PLDHashNumber
PL_DHashVoidPtrKeyStub(PLDHashTable *table, const void *key);
NS_COM_GLUE PRBool
PL_DHashMatchEntryStub(PLDHashTable *table,
const PLDHashEntryHdr *entry,
const void *key);
NS_COM_GLUE PRBool
PL_DHashMatchStringKey(PLDHashTable *table,
const PLDHashEntryHdr *entry,
const void *key);
NS_COM_GLUE void
PL_DHashMoveEntryStub(PLDHashTable *table,
const PLDHashEntryHdr *from,
PLDHashEntryHdr *to);
NS_COM_GLUE void
PL_DHashClearEntryStub(PLDHashTable *table, PLDHashEntryHdr *entry);
NS_COM_GLUE void
PL_DHashFreeStringKey(PLDHashTable *table, PLDHashEntryHdr *entry);
NS_COM_GLUE void
PL_DHashFinalizeStub(PLDHashTable *table);
/*
* If you use PLDHashEntryStub or a subclass of it as your entry struct, and
* if your entries move via memcpy and clear via memset(0), you can use these
* stub operations.
*/
NS_COM_GLUE const PLDHashTableOps *
PL_DHashGetStubOps(void);
/*
* Dynamically allocate a new PLDHashTable using malloc, initialize it using
* PL_DHashTableInit, and return its address. Return null on malloc failure.
* Note that the entry storage at table->entryStore will be allocated using
* the ops->allocTable callback.
*/
NS_COM_GLUE PLDHashTable *
PL_NewDHashTable(const PLDHashTableOps *ops, void *data, PRUint32 entrySize,
PRUint32 capacity);
/*
* Finalize table's data, free its entry storage (via table->ops->freeTable),
* and return the memory starting at table to the malloc heap.
*/
NS_COM_GLUE void
PL_DHashTableDestroy(PLDHashTable *table);
/*
* Initialize table with ops, data, entrySize, and capacity. Capacity is a
* guess for the smallest table size at which the table will usually be less
* than 75% loaded (the table will grow or shrink as needed; capacity serves
* only to avoid inevitable early growth from PL_DHASH_MIN_SIZE).
*/
NS_COM_GLUE PRBool
PL_DHashTableInit(PLDHashTable *table, const PLDHashTableOps *ops, void *data,
PRUint32 entrySize, PRUint32 capacity);
/*
* Set maximum and minimum alpha for table. The defaults are 0.75 and .25.
* maxAlpha must be in [0.5, 0.9375] for the default PL_DHASH_MIN_SIZE; or if
* MinSize=PL_DHASH_MIN_SIZE <= 256, in [0.5, (float)(MinSize-1)/MinSize]; or
* else in [0.5, 255.0/256]. minAlpha must be in [0, maxAlpha / 2), so that
* we don't shrink on the very next remove after growing a table upon adding
* an entry that brings entryCount past maxAlpha * tableSize.
*/
NS_COM_GLUE void
PL_DHashTableSetAlphaBounds(PLDHashTable *table,
float maxAlpha,
float minAlpha);
/*
* Call this macro with k, the number of pointer-sized words wasted per entry
* under chaining, to compute the minimum alpha at which double hashing still
* beats chaining.
*/
#define PL_DHASH_MIN_ALPHA(table, k) \
((float)((table)->entrySize / sizeof(void *) - 1) \
/ ((table)->entrySize / sizeof(void *) + (k)))
/*
* Finalize table's data, free its entry storage using table->ops->freeTable,
* and leave its members unchanged from their last live values (which leaves
* pointers dangling). If you want to burn cycles clearing table, it's up to
* your code to call memset.
*/
NS_COM_GLUE void
PL_DHashTableFinish(PLDHashTable *table);
/*
* To consolidate keyHash computation and table grow/shrink code, we use a
* single entry point for lookup, add, and remove operations. The operation
* codes are declared here, along with codes returned by PLDHashEnumerator
* functions, which control PL_DHashTableEnumerate's behavior.
*/
typedef enum PLDHashOperator {
PL_DHASH_LOOKUP = 0, /* lookup entry */
PL_DHASH_ADD = 1, /* add entry */
PL_DHASH_REMOVE = 2, /* remove entry, or enumerator says remove */
PL_DHASH_NEXT = 0, /* enumerator says continue */
PL_DHASH_STOP = 1 /* enumerator says stop */
} PLDHashOperator;
/*
* To lookup a key in table, call:
*
* entry = PL_DHashTableOperate(table, key, PL_DHASH_LOOKUP);
*
* If PL_DHASH_ENTRY_IS_BUSY(entry) is true, key was found and it identifies
* entry. If PL_DHASH_ENTRY_IS_FREE(entry) is true, key was not found.
*
* To add an entry identified by key to table, call:
*
* entry = PL_DHashTableOperate(table, key, PL_DHASH_ADD);
*
* If entry is null upon return, then either the table is severely overloaded,
* and memory can't be allocated for entry storage via table->ops->allocTable;
* Or if table->ops->initEntry is non-null, the table->ops->initEntry op may
* have returned false.
*
* Otherwise, entry->keyHash has been set so that PL_DHASH_ENTRY_IS_BUSY(entry)
* is true, and it is up to the caller to initialize the key and value parts
* of the entry sub-type, if they have not been set already (i.e. if entry was
* not already in the table, and if the optional initEntry hook was not used).
*
* To remove an entry identified by key from table, call:
*
* (void) PL_DHashTableOperate(table, key, PL_DHASH_REMOVE);
*
* If key's entry is found, it is cleared (via table->ops->clearEntry) and
* the entry is marked so that PL_DHASH_ENTRY_IS_FREE(entry). This operation
* returns null unconditionally; you should ignore its return value.
*/
NS_COM_GLUE PLDHashEntryHdr * PL_DHASH_FASTCALL
PL_DHashTableOperate(PLDHashTable *table, const void *key, PLDHashOperator op);
/*
* Remove an entry already accessed via LOOKUP or ADD.
*
* NB: this is a "raw" or low-level routine, intended to be used only where
* the inefficiency of a full PL_DHashTableOperate (which rehashes in order
* to find the entry given its key) is not tolerable. This function does not
* shrink the table if it is underloaded. It does not update stats #ifdef
* PL_DHASHMETER, either.
*/
NS_COM_GLUE void
PL_DHashTableRawRemove(PLDHashTable *table, PLDHashEntryHdr *entry);
/*
* Enumerate entries in table using etor:
*
* count = PL_DHashTableEnumerate(table, etor, arg);
*
* PL_DHashTableEnumerate calls etor like so:
*
* op = etor(table, entry, number, arg);
*
* where number is a zero-based ordinal assigned to live entries according to
* their order in table->entryStore.
*
* The return value, op, is treated as a set of flags. If op is PL_DHASH_NEXT,
* then continue enumerating. If op contains PL_DHASH_REMOVE, then clear (via
* table->ops->clearEntry) and free entry. Then we check whether op contains
* PL_DHASH_STOP; if so, stop enumerating and return the number of live entries
* that were enumerated so far. Return the total number of live entries when
* enumeration completes normally.
*
* If etor calls PL_DHashTableOperate on table with op != PL_DHASH_LOOKUP, it
* must return PL_DHASH_STOP; otherwise undefined behavior results.
*
* If any enumerator returns PL_DHASH_REMOVE, table->entryStore may be shrunk
* or compressed after enumeration, but before PL_DHashTableEnumerate returns.
* Such an enumerator therefore can't safely set aside entry pointers, but an
* enumerator that never returns PL_DHASH_REMOVE can set pointers to entries
* aside, e.g., to avoid copying live entries into an array of the entry type.
* Copying entry pointers is cheaper, and safe so long as the caller of such a
* "stable" Enumerate doesn't use the set-aside pointers after any call either
* to PL_DHashTableOperate, or to an "unstable" form of Enumerate, which might
* grow or shrink entryStore.
*
* If your enumerator wants to remove certain entries, but set aside pointers
* to other entries that it retains, it can use PL_DHashTableRawRemove on the
* entries to be removed, returning PL_DHASH_NEXT to skip them. Likewise, if
* you want to remove entries, but for some reason you do not want entryStore
* to be shrunk or compressed, you can call PL_DHashTableRawRemove safely on
* the entry being enumerated, rather than returning PL_DHASH_REMOVE.
*/
typedef PLDHashOperator
(* PR_CALLBACK PLDHashEnumerator)(PLDHashTable *table, PLDHashEntryHdr *hdr,
PRUint32 number, void *arg);
NS_COM_GLUE PRUint32
PL_DHashTableEnumerate(PLDHashTable *table, PLDHashEnumerator etor, void *arg);
#ifdef PL_DHASHMETER
#include <stdio.h>
NS_COM_GLUE void
PL_DHashTableDumpMeter(PLDHashTable *table, PLDHashEnumerator dump, FILE *fp);
#endif
PR_END_EXTERN_C
#endif /* pldhash_h___ */
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