зеркало из https://github.com/mozilla/pjs.git
444 строки
17 KiB
C
444 строки
17 KiB
C
/* -*- Mode: C; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
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*
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* The contents of this file are subject to the Netscape Public
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* License Version 1.1 (the "License"); you may not use this file
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* except in compliance with the License. You may obtain a copy of
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* the License at http://www.mozilla.org/NPL/
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*
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* Software distributed under the License is distributed on an "AS
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* IS" basis, WITHOUT WARRANTY OF ANY KIND, either express oqr
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* implied. See the License for the specific language governing
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* rights and limitations under the License.
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*
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* The Original Code is Mozilla JavaScript code.
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*
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* The Initial Developer of the Original Code is Netscape
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* Communications Corporation. Portions created by Netscape are
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* Copyright (C) 1999,2000 Netscape Communications Corporation.
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* All Rights Reserved.
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*
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* Original Contributor:
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* Brendan Eich <brendan@mozilla.org>
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*
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* Contributor(s):
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*
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* Alternatively, the contents of this file may be used under the
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* terms of the GNU Public License (the "GPL"), in which case the
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* provisions of the GPL are applicable instead of those above.
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* If you wish to allow use of your version of this file only
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* under the terms of the GPL and not to allow others to use your
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* version of this file under the NPL, indicate your decision by
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* deleting the provisions above and replace them with the notice
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* and other provisions required by the GPL. If you do not delete
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* the provisions above, a recipient may use your version of this
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* file under either the NPL or the GPL.
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*/
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#ifndef pldhash_h___
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#define pldhash_h___
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/*
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* Double hashing, a la Knuth 6.
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* GENERATED BY js/src/plify_jsdhash.sed -- DO NOT EDIT!!!
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*/
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#include "prtypes.h"
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PR_BEGIN_EXTERN_C
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/* Minimum table size, or gross entry count (net is at most .75 loaded). */
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#ifndef PL_DHASH_MIN_SIZE
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#define PL_DHASH_MIN_SIZE 16
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#endif
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/*
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* Multiplicative hash uses an unsigned 32 bit integer and the golden ratio,
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* expressed as a fixed-point 32-bit fraction.
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*/
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#define PL_DHASH_BITS 32
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#define PL_DHASH_GOLDEN_RATIO 0x9E3779B9U
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/* Primitive and forward-struct typedefs. */
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typedef PRUint32 PLDHashNumber;
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typedef struct PLDHashEntryHdr PLDHashEntryHdr;
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typedef struct PLDHashEntryStub PLDHashEntryStub;
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typedef struct PLDHashTable PLDHashTable;
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typedef struct PLDHashTableOps PLDHashTableOps;
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/*
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* Table entry header structure.
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*
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* In order to allow in-line allocation of key and value, we do not declare
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* either here. Instead, the API uses const void *key as a formal parameter,
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* and asks each entry for its key when necessary via a getKey callback, used
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* when growing or shrinking the table. Other callback types are defined
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* below and grouped into the PLDHashTableOps structure, for single static
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* initialization per hash table sub-type.
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*
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* Each hash table sub-type should nest the PLDHashEntryHdr structure at the
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* front of its particular entry type. The keyHash member contains the result
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* of multiplying the hash code returned from the hashKey callback (see below)
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* by PL_DHASH_GOLDEN_RATIO. Its value is table size invariant. keyHash is
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* maintained automatically by PL_DHashTableOperate -- users should never set
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* it, and its only uses should be via the entry macros below.
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*/
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struct PLDHashEntryHdr {
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PLDHashNumber keyHash; /* every entry must begin like this */
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};
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#define PL_DHASH_ENTRY_IS_FREE(entry) ((entry)->keyHash == 0)
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#define PL_DHASH_ENTRY_IS_BUSY(entry) (!PL_DHASH_ENTRY_IS_FREE(entry))
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/*
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* A PLDHashTable is currently 8 words (without the PL_DHASHMETER overhead)
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* on most architectures, and may be allocated on the stack or within another
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* structure or class (see below for the Init and Finish functions to use).
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*
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* To decide whether to use double hashing vs. chaining, we need to develop a
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* trade-off relation, as follows:
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*
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* Let alpha be the load factor, esize the entry size in words, count the
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* entry count, and pow2 the power-of-two table size in entries.
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*
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* (PLDHashTable overhead) > (PLHashTable overhead)
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* (unused table entry space) > (malloc and .next overhead per entry) +
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* (buckets overhead)
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* (1 - alpha) * esize * pow2 > 2 * count + pow2
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*
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* Notice that alpha is by definition (count / pow2):
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*
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* (1 - alpha) * esize * pow2 > 2 * alpha * pow2 + pow2
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* (1 - alpha) * esize > 2 * alpha + 1
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*
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* esize > (1 + 2 * alpha) / (1 - alpha)
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*
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* This assumes both tables must keep keyHash, key, and value for each entry,
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* where key and value point to separately allocated strings or structures.
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* If key and value can be combined into one pointer, then the trade-off is:
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*
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* esize > (1 + 3 * alpha) / (1 - alpha)
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*
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* If the entry value can be a subtype of PLDHashEntryHdr, rather than a type
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* that must be allocated separately and referenced by an entry.value pointer
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* member, and provided key's allocation can be fused with its entry's, then
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* k (the words wasted per entry with chaining) is 4.
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*
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* To see these curves, feed gnuplot input like so:
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*
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* gnuplot> f(x,k) = (1 + k * x) / (1 - x)
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* gnuplot> plot [0:.75] f(x,2), f(x,3), f(x,4)
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*
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* For k of 2 and a well-loaded table (alpha > .5), esize must be more than 4
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* words for chaining to be more space-efficient than double hashing.
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*
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* Solving for alpha helps us decide when to shrink an underloaded table:
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*
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* esize > (1 + k * alpha) / (1 - alpha)
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* esize - alpha * esize > 1 + k * alpha
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* esize - 1 > (k + esize) * alpha
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* (esize - 1) / (k + esize) > alpha
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*
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* alpha < (esize - 1) / (esize + k)
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*
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* Therefore double hashing should keep alpha >= (esize - 1) / (esize + k),
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* assuming esize is not too large (in which case, chaining should probably be
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* used for any alpha). For esize=2 and k=3, we want alpha >= .2; for esize=3
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* and k=2, we want alpha >= .4. For k=4, esize could be 6, and alpha >= .5
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* would still obtain.
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*
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* The current implementation uses a constant .25 as alpha's lower bound when
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* deciding to shrink the table (while respecting PL_DHASH_MIN_SIZE).
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*
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* Note a qualitative difference between chaining and double hashing: under
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* chaining, entry addresses are stable across table shrinks and grows. With
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* double hashing, you can't safely hold an entry pointer and use it after an
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* ADD or REMOVE operation.
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*
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* The moral of this story: there is no one-size-fits-all hash table scheme,
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* but for small table entry size, and assuming entry address stability is not
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* required, double hashing wins.
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*/
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struct PLDHashTable {
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PLDHashTableOps *ops; /* virtual operations, see below */
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void *data; /* ops- and instance-specific data */
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PRInt16 hashShift; /* multiplicative hash shift */
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PRInt16 sizeLog2; /* log2(table size) */
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PRUint32 sizeMask; /* PR_BITMASK(log2(table size)) */
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PRUint32 entrySize; /* number of bytes in an entry */
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PRUint32 entryCount; /* number of entries in table */
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PRUint32 removedCount; /* removed entry sentinels in table */
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char *entryStore; /* entry storage */
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#ifdef PL_DHASHMETER
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struct PLDHashStats {
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PRUint32 searches; /* total number of table searches */
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PRUint32 steps; /* hash chain links traversed */
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PRUint32 hits; /* searches that found key */
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PRUint32 misses; /* searches that didn't find key */
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PRUint32 lookups; /* number of PL_DHASH_LOOKUPs */
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PRUint32 addMisses; /* adds that miss, and do work */
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PRUint32 addHits; /* adds that hit an existing entry */
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PRUint32 addFailures; /* out-of-memory during add growth */
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PRUint32 removeHits; /* removes that hit, and do work */
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PRUint32 removeMisses; /* useless removes that miss */
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PRUint32 removeEnums; /* removes done by Enumerate */
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PRUint32 grows; /* table expansions */
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PRUint32 shrinks; /* table contractions */
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PRUint32 compresses; /* table compressions */
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PRUint32 enumShrinks; /* contractions after Enumerate */
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} stats;
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#endif
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};
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/*
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* Table space at entryStore is allocated and freed using these callbacks.
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* The allocator should return null on error only (not if called with nbytes
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* equal to 0; but note that jsdhash.c code will never call with 0 nbytes).
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*/
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typedef void *
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(* PR_CALLBACK PLDHashAllocTable)(PLDHashTable *table, PRUint32 nbytes);
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typedef void
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(* PR_CALLBACK PLDHashFreeTable) (PLDHashTable *table, void *ptr);
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/*
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* When a table grows or shrinks, each entry is queried for its key using this
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* callback. NB: in that event, entry is not in table any longer; it's in the
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* old entryStore vector, which is due to be freed once all entries have been
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* moved via moveEntry callbacks.
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*/
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typedef const void *
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(* PR_CALLBACK PLDHashGetKey) (PLDHashTable *table, PLDHashEntryHdr *entry);
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/*
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* Compute the hash code for a given key to be looked up, added, or removed
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* from table. A hash code may have any PLDHashNumber value.
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*/
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typedef PLDHashNumber
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(* PR_CALLBACK PLDHashHashKey) (PLDHashTable *table, const void *key);
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/*
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* Compare the key identifying entry in table with the provided key parameter.
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* Return PR_TRUE if keys match, PR_FALSE otherwise.
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*/
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typedef PRBool
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(* PR_CALLBACK PLDHashMatchEntry)(PLDHashTable *table,
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const PLDHashEntryHdr *entry,
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const void *key);
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/*
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* Copy the data starting at from to the new entry storage at to. Do not add
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* reference counts for any strong references in the entry, however, as this
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* is a "move" operation: the old entry storage at from will be freed without
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* any reference-decrementing callback shortly.
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*/
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typedef void
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(* PR_CALLBACK PLDHashMoveEntry)(PLDHashTable *table,
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const PLDHashEntryHdr *from,
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PLDHashEntryHdr *to);
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/*
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* Clear the entry and drop any strong references it holds. This callback is
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* invoked during a PL_DHASH_REMOVE operation (see below for operation codes),
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* but only if the given key is found in the table.
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*/
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typedef void
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(* PR_CALLBACK PLDHashClearEntry)(PLDHashTable *table, PLDHashEntryHdr *entry);
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/*
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* Called when a table (whether allocated dynamically by itself, or nested in
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* a larger structure, or allocated on the stack) is finished. This callback
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* allows table->ops-specific code to finalize table->data.
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*/
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typedef void
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(* PR_CALLBACK PLDHashFinalize) (PLDHashTable *table);
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/* Finally, the "vtable" structure for PLDHashTable. */
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struct PLDHashTableOps {
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PLDHashAllocTable allocTable;
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PLDHashFreeTable freeTable;
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PLDHashGetKey getKey;
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PLDHashHashKey hashKey;
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PLDHashMatchEntry matchEntry;
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PLDHashMoveEntry moveEntry;
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PLDHashClearEntry clearEntry;
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PLDHashFinalize finalize;
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};
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/*
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* Default implementations for the above ops.
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*/
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PR_EXTERN(void *)
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PL_DHashAllocTable(PLDHashTable *table, PRUint32 nbytes);
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PR_EXTERN(void)
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PL_DHashFreeTable(PLDHashTable *table, void *ptr);
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PR_EXTERN(PLDHashNumber)
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PL_DHashStringKey(PLDHashTable *table, const void *key);
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/* A minimal entry contains a keyHash header and a void key pointer. */
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struct PLDHashEntryStub {
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PLDHashEntryHdr hdr;
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const void *key;
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};
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PR_EXTERN(const void *)
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PL_DHashGetKeyStub(PLDHashTable *table, PLDHashEntryHdr *entry);
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PR_EXTERN(PLDHashNumber)
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PL_DHashVoidPtrKeyStub(PLDHashTable *table, const void *key);
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PR_EXTERN(PRBool)
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PL_DHashMatchEntryStub(PLDHashTable *table,
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const PLDHashEntryHdr *entry,
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const void *key);
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PR_EXTERN(void)
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PL_DHashMoveEntryStub(PLDHashTable *table,
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const PLDHashEntryHdr *from,
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PLDHashEntryHdr *to);
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PR_EXTERN(void)
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PL_DHashClearEntryStub(PLDHashTable *table, PLDHashEntryHdr *entry);
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PR_EXTERN(void)
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PL_DHashFinalizeStub(PLDHashTable *table);
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/*
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* If you use PLDHashEntryStub or a subclass of it as your entry struct, and
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* if your entries move via memcpy and clear via memset(0), you can use these
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* stub operations.
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*/
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PR_EXTERN(PLDHashTableOps *)
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PL_DHashGetStubOps(void);
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/*
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* Dynamically allocate a new PLDHashTable using malloc, initialize it using
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* PL_DHashTableInit, and return its address. Return null on malloc failure.
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* Note that the entry storage at table->entryStore will be allocated using
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* the ops->allocTable callback.
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*/
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PR_EXTERN(PLDHashTable *)
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PR_NewDHashTable(PLDHashTableOps *ops, void *data, PRUint32 entrySize,
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PRUint32 capacity);
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/*
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* Finalize table's data, free its entry storage (via table->ops->freeTable),
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* and return the memory starting at table to the malloc heap.
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*/
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PR_EXTERN(void)
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PL_DHashTableDestroy(PLDHashTable *table);
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/*
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* Initialize table with ops, data, entrySize, and capacity. Capacity is a
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* guess for the smallest table size at which the table will usually be less
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* than 75% loaded (the table will grow or shrink as needed; capacity serves
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* only to avoid inevitable early growth from PL_DHASH_MIN_SIZE).
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*/
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PR_EXTERN(PRBool)
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PL_DHashTableInit(PLDHashTable *table, PLDHashTableOps *ops, void *data,
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PRUint32 entrySize, PRUint32 capacity);
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/*
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* Finalize table's data, free its entry storage using table->ops->freeTable,
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* and leave its members unchanged from their last live values (which leaves
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* pointers dangling). If you want to burn cycles clearing table, it's up to
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* your code to call memset.
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*/
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PR_EXTERN(void)
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PL_DHashTableFinish(PLDHashTable *table);
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/*
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* To consolidate keyHash computation and table grow/shrink code, we use a
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* single entry point for lookup, add, and remove operations. The operation
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* codes are declared here, along with codes returned by PLDHashEnumerator
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* functions, which control PL_DHashTableEnumerate's behavior.
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*/
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typedef enum PLDHashOperator {
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PL_DHASH_LOOKUP = 0, /* lookup entry */
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PL_DHASH_ADD = 1, /* add entry */
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PL_DHASH_REMOVE = 2, /* remove entry, or enumerator says remove */
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PL_DHASH_NEXT = 0, /* enumerator says continue */
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PL_DHASH_STOP = 1 /* enumerator says stop */
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} PLDHashOperator;
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/*
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* To lookup a key in table, call:
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*
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* entry = PL_DHashTableOperate(table, key, PL_DHASH_LOOKUP);
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*
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* If PL_DHASH_ENTRY_IS_BUSY(entry) is true, key was found and it identifies
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* entry. If PL_DHASH_ENTRY_IS_FREE(entry) is true, key was not found.
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*
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* To add an entry identified by key to table, call:
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*
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* entry = PL_DHashTableOperate(table, key, PL_DHASH_ADD);
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*
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* If entry is null upon return, the table is severely overloaded, and new
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* memory can't be allocated for new entry storage via table->ops->allocTable.
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* Otherwise, entry->keyHash has been set so that PL_DHASH_ENTRY_IS_BUSY(entry)
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* is true, and it is up to the caller to initialize the key and value parts
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* of the entry sub-type, if they have not been set already (i.e. if entry was
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* not already in the table).
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*
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* To remove an entry identified by key from table, call:
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*
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* (void) PL_DHashTableOperate(table, key, PL_DHASH_REMOVE);
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*
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* If key's entry is found, it is cleared (via table->ops->clearEntry) and
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* the entry is marked so that PL_DHASH_ENTRY_IS_FREE(entry). This operation
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* returns null unconditionally; you should ignore its return value.
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*/
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PR_EXTERN(PLDHashEntryHdr *)
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PL_DHashTableOperate(PLDHashTable *table, const void *key, PLDHashOperator op);
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/*
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* Remove an entry already accessed via LOOKUP or ADD.
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*
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* NB: this is a "raw" or low-level routine, intended to be used only where
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* the inefficiency of a full PL_DHashTableOperate (which rehashes in order
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* to find the entry given its key) is not tolerable. This function does not
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* shrink the table if it is underloaded. It does not update stats #ifdef
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* PL_DHASHMETER, either.
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*/
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PR_EXTERN(void)
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PL_DHashTableRawRemove(PLDHashTable *table, PLDHashEntryHdr *entry);
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/*
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* Enumerate entries in table using etor:
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*
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* count = PL_DHashTableEnumerate(table, etor, arg);
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*
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* PL_DHashTableEnumerate calls etor like so:
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*
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* op = etor(table, entry, number, arg);
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*
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* where number is a zero-based ordinal assigned to live entries according to
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* their order in table->entryStore.
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*
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* The return value, op, is treated as a set of flags. If op is PL_DHASH_NEXT,
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* then continue enumerating. If op contains PL_DHASH_REMOVE, then clear (via
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* table->ops->clearEntry) and free entry. Then we check whether op contains
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* PL_DHASH_STOP; if so, stop enumerating and return the number of live entries
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* that were enumerated so far. Return the total number of live entries when
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* enumeration completes normally.
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*
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* If etor calls PL_DHashTableOperate on table, it must return PL_DHASH_STOP;
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* otherwise undefined behavior results.
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*/
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typedef PLDHashOperator
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(* PR_CALLBACK PLDHashEnumerator)(PLDHashTable *table, PLDHashEntryHdr *hdr,
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PRUint32 number, void *arg);
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PR_EXTERN(PRUint32)
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PL_DHashTableEnumerate(PLDHashTable *table, PLDHashEnumerator etor, void *arg);
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#ifdef PL_DHASHMETER
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#include <stdio.h>
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PR_EXTERN(void)
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PL_DHashTableDumpMeter(PLDHashTable *table, PLDHashEnumerator dump, FILE *fp);
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#endif
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PR_END_EXTERN_C
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#endif /* pldhash_h___ */
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