jsdhash.c

来自「一个基于alice开发的机器人」· C语言 代码 · 共 764 行 · 第 1/2 页

/* -*- 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 <[e-mail]> (Original Author)
 *   Chris Waterson <[e-mail]>
 *
 * 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 ***** */

/*
 * Double hashing implementation.
 */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "jsbit.h"
#include "jsdhash.h"
#include "jsutil.h"     /* for JS_ASSERT */

#ifdef JS_DHASHMETER
# if defined MOZILLA_CLIENT && defined DEBUG_XXXbrendan
#  include "nsTraceMalloc.h"
# endif
# define METER(x)       x
#else
# define METER(x)       /* nothing */
#endif

JS_PUBLIC_API(void *)
JS_DHashAllocTable(JSDHashTable *table, uint32 nbytes)
{
    return malloc(nbytes);
}

JS_PUBLIC_API(void)
JS_DHashFreeTable(JSDHashTable *table, void *ptr)
{
    free(ptr);
}

JS_PUBLIC_API(JSDHashNumber)
JS_DHashStringKey(JSDHashTable *table, const void *key)
{
    JSDHashNumber h;
    const unsigned char *s;

    h = 0;
    for (s = key; *s != '\0'; s++)
        h = (h >> (JS_DHASH_BITS - 4)) ^ (h << 4) ^ *s;
    return h;
}

JS_PUBLIC_API(const void *)
JS_DHashGetKeyStub(JSDHashTable *table, JSDHashEntryHdr *entry)
{
    JSDHashEntryStub *stub = (JSDHashEntryStub *)entry;

    return stub->key;
}

JS_PUBLIC_API(JSDHashNumber)
JS_DHashVoidPtrKeyStub(JSDHashTable *table, const void *key)
{
    return (JSDHashNumber)key >> 2;
}

JS_PUBLIC_API(JSBool)
JS_DHashMatchEntryStub(JSDHashTable *table,
                       const JSDHashEntryHdr *entry,
                       const void *key)
{
    const JSDHashEntryStub *stub = (const JSDHashEntryStub *)entry;

    return stub->key == key;
}

JS_PUBLIC_API(JSBool)
JS_DHashMatchStringKey(JSDHashTable *table,
                       const JSDHashEntryHdr *entry,
                       const void *key)
{
    const JSDHashEntryStub *stub = (const JSDHashEntryStub *)entry;

    /* XXX tolerate null keys on account of sloppy Mozilla callers. */
    return stub->key == key ||
           (stub->key && key && strcmp(stub->key, key) == 0);
}

JS_PUBLIC_API(void)
JS_DHashMoveEntryStub(JSDHashTable *table,
                      const JSDHashEntryHdr *from,
                      JSDHashEntryHdr *to)
{
    memcpy(to, from, table->entrySize);
}

JS_PUBLIC_API(void)
JS_DHashClearEntryStub(JSDHashTable *table, JSDHashEntryHdr *entry)
{
    memset(entry, 0, table->entrySize);
}

JS_PUBLIC_API(void)
JS_DHashFreeStringKey(JSDHashTable *table, JSDHashEntryHdr *entry)
{
    const JSDHashEntryStub *stub = (const JSDHashEntryStub *)entry;

    free((void *) stub->key);
    memset(entry, 0, table->entrySize);
}

JS_PUBLIC_API(void)
JS_DHashFinalizeStub(JSDHashTable *table)
{
}

static const JSDHashTableOps stub_ops = {
    JS_DHashAllocTable,
    JS_DHashFreeTable,
    JS_DHashGetKeyStub,
    JS_DHashVoidPtrKeyStub,
    JS_DHashMatchEntryStub,
    JS_DHashMoveEntryStub,
    JS_DHashClearEntryStub,
    JS_DHashFinalizeStub,
    NULL
};

JS_PUBLIC_API(const JSDHashTableOps *)
JS_DHashGetStubOps(void)
{
    return &stub_ops;
}

JS_PUBLIC_API(JSDHashTable *)
JS_NewDHashTable(const JSDHashTableOps *ops, void *data, uint32 entrySize,
                 uint32 capacity)
{
    JSDHashTable *table;

    table = (JSDHashTable *) malloc(sizeof *table);
    if (!table)
        return NULL;
    if (!JS_DHashTableInit(table, ops, data, entrySize, capacity)) {
        free(table);
        return NULL;
    }
    return table;
}

JS_PUBLIC_API(void)
JS_DHashTableDestroy(JSDHashTable *table)
{
    JS_DHashTableFinish(table);
    free(table);
}

JS_PUBLIC_API(JSBool)
JS_DHashTableInit(JSDHashTable *table, const JSDHashTableOps *ops, void *data,
                  uint32 entrySize, uint32 capacity)
{
    int log2;
    uint32 nbytes;

#ifdef DEBUG
    if (entrySize > 10 * sizeof(void *)) {
        fprintf(stderr,
                "jsdhash: for the table at address %p, the given entrySize"
                " of %lu %s favors chaining over double hashing.\n",
                (void *)table,
                (unsigned long) entrySize,
                (entrySize > 16 * sizeof(void*)) ? "definitely" : "probably");
    }
#endif

    table->ops = ops;
    table->data = data;
    if (capacity < JS_DHASH_MIN_SIZE)
        capacity = JS_DHASH_MIN_SIZE;
    log2 = JS_CeilingLog2(capacity);
    capacity = JS_BIT(log2);
    if (capacity >= JS_DHASH_SIZE_LIMIT)
        return JS_FALSE;
    table->hashShift = JS_DHASH_BITS - log2;
    table->maxAlphaFrac = 0xC0;                 /* .75 */
    table->minAlphaFrac = 0x40;                 /* .25 */
    table->entrySize = entrySize;
    table->entryCount = table->removedCount = 0;
    table->generation = 0;
    nbytes = capacity * entrySize;

    table->entryStore = ops->allocTable(table, nbytes);
    if (!table->entryStore)
        return JS_FALSE;
    memset(table->entryStore, 0, nbytes);
    METER(memset(&table->stats, 0, sizeof table->stats));
    return JS_TRUE;
}

/*
 * Compute max and min load numbers (entry counts) from table params.
 */
#define MAX_LOAD(table, size)   (((table)->maxAlphaFrac * (size)) >> 8)
#define MIN_LOAD(table, size)   (((table)->minAlphaFrac * (size)) >> 8)

JS_PUBLIC_API(void)
JS_DHashTableSetAlphaBounds(JSDHashTable *table,
                            float maxAlpha,
                            float minAlpha)
{
    uint32 size;

    /*
     * Reject obviously insane bounds, rather than trying to guess what the
     * buggy caller intended.
     */
    JS_ASSERT(0.5 <= maxAlpha && maxAlpha < 1 && 0 <= minAlpha);
    if (maxAlpha < 0.5 || 1 <= maxAlpha || minAlpha < 0)
        return;

    /*
     * Ensure that at least one entry will always be free.  If maxAlpha at
     * minimum size leaves no entries free, reduce maxAlpha based on minimum
     * size and the precision limit of maxAlphaFrac's fixed point format.
     */
    JS_ASSERT(JS_DHASH_MIN_SIZE - (maxAlpha * JS_DHASH_MIN_SIZE) >= 1);
    if (JS_DHASH_MIN_SIZE - (maxAlpha * JS_DHASH_MIN_SIZE) < 1) {
        maxAlpha = (float)
                   (JS_DHASH_MIN_SIZE - JS_MAX(JS_DHASH_MIN_SIZE / 256, 1))
                   / JS_DHASH_MIN_SIZE;
    }

    /*
     * Ensure that minAlpha is strictly less than half maxAlpha.  Take care
     * not to truncate an entry's worth of alpha when storing in minAlphaFrac
     * (8-bit fixed point format).
     */
    JS_ASSERT(minAlpha < maxAlpha / 2);
    if (minAlpha >= maxAlpha / 2) {
        size = JS_DHASH_TABLE_SIZE(table);
        minAlpha = (size * maxAlpha - JS_MAX(size / 256, 1)) / (2 * size);
    }

    table->maxAlphaFrac = (uint8)(maxAlpha * 256);
    table->minAlphaFrac = (uint8)(minAlpha * 256);
}

/*
 * Double hashing needs the second hash code to be relatively prime to table
 * size, so we simply make hash2 odd.
 */
#define HASH1(hash0, shift)         ((hash0) >> (shift))
#define HASH2(hash0,log2,shift)     ((((hash0) << (log2)) >> (shift)) | 1)

/*
 * Reserve keyHash 0 for free entries and 1 for removed-entry sentinels.  Note
 * that a removed-entry sentinel need be stored only if the removed entry had
 * a colliding entry added after it.  Therefore we can use 1 as the collision
 * flag in addition to the removed-entry sentinel value.  Multiplicative hash
 * uses the high order bits of keyHash, so this least-significant reservation
 * should not hurt the hash function's effectiveness much.
 *
 * If you change any of these magic numbers, also update JS_DHASH_ENTRY_IS_LIVE
 * in jsdhash.h.  It used to be private to jsdhash.c, but then became public to
 * assist iterator writers who inspect table->entryStore directly.
 */
#define COLLISION_FLAG              ((JSDHashNumber) 1)
#define MARK_ENTRY_FREE(entry)      ((entry)->keyHash = 0)
#define MARK_ENTRY_REMOVED(entry)   ((entry)->keyHash = 1)
#define ENTRY_IS_REMOVED(entry)     ((entry)->keyHash == 1)
#define ENTRY_IS_LIVE(entry)        JS_DHASH_ENTRY_IS_LIVE(entry)
#define ENSURE_LIVE_KEYHASH(hash0)  if (hash0 < 2) hash0 -= 2; else (void)0

/* Match an entry's keyHash against an unstored one computed from a key. */
#define MATCH_ENTRY_KEYHASH(entry,hash0) \
    (((entry)->keyHash & ~COLLISION_FLAG) == (hash0))

/* Compute the address of the indexed entry in table. */
#define ADDRESS_ENTRY(table, index) \
    ((JSDHashEntryHdr *)((table)->entryStore + (index) * (table)->entrySize))

JS_PUBLIC_API(void)
JS_DHashTableFinish(JSDHashTable *table)
{
    char *entryAddr, *entryLimit;
    uint32 entrySize;
    JSDHashEntryHdr *entry;

#ifdef DEBUG_XXXbrendan
    static FILE *dumpfp = NULL;
    if (!dumpfp) dumpfp = fopen("/tmp/jsdhash.bigdump", "w");
    if (dumpfp) {
#ifdef MOZILLA_CLIENT
        NS_TraceStack(1, dumpfp);
#endif
        JS_DHashTableDumpMeter(table, NULL, dumpfp);
        fputc('\n', dumpfp);
    }
#endif

    /* Call finalize before clearing entries, so it can enumerate them. */
    table->ops->finalize(table);

    /* Clear any remaining live entries. */
    entryAddr = table->entryStore;
    entrySize = table->entrySize;
    entryLimit = entryAddr + JS_DHASH_TABLE_SIZE(table) * entrySize;
    while (entryAddr < entryLimit) {
        entry = (JSDHashEntryHdr *)entryAddr;
        if (ENTRY_IS_LIVE(entry)) {
            METER(table->stats.removeEnums++);
            table->ops->clearEntry(table, entry);
        }
        entryAddr += entrySize;
    }

    /* Free entry storage last. */
    table->ops->freeTable(table, table->entryStore);
}

static JSDHashEntryHdr *
SearchTable(JSDHashTable *table, const void *key, JSDHashNumber keyHash,
            JSDHashOperator op)
{
    JSDHashNumber hash1, hash2;
    int hashShift, sizeLog2;
    JSDHashEntryHdr *entry, *firstRemoved;
    JSDHashMatchEntry matchEntry;
    uint32 sizeMask;

    METER(table->stats.searches++);
    JS_ASSERT(!(keyHash & COLLISION_FLAG));

    /* Compute the primary hash address. */
    hashShift = table->hashShift;
    hash1 = HASH1(keyHash, hashShift);
    entry = ADDRESS_ENTRY(table, hash1);

    /* Miss: return space for a new entry. */
    if (JS_DHASH_ENTRY_IS_FREE(entry)) {
        METER(table->stats.misses++);
        return entry;
    }

    /* Hit: return entry. */
    matchEntry = table->ops->matchEntry;
    if (MATCH_ENTRY_KEYHASH(entry, keyHash) && matchEntry(table, entry, key)) {
        METER(table->stats.hits++);
        return entry;
    }

    /* Collision: double hash. */