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gecko-dev/js/jsd/jshash.cpp

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12 KiB
C++
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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
* vim: set ts=8 sts=4 et sw=4 tw=99:
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
/*
* PR hash table package.
*/
#include "jshash.h"
#include "mozilla/MathAlgorithms.h"
#include <stdlib.h>
#include <string.h>
#include "jstypes.h"
#include "js/Utility.h"
using namespace js;
using mozilla::CeilingLog2Size;
using mozilla::RotateLeft;
/* Compute the number of buckets in ht */
#define NBUCKETS(ht) JS_BIT(JS_HASH_BITS - (ht)->shift)
/* The smallest table has 16 buckets */
#define MINBUCKETSLOG2 4
#define MINBUCKETS JS_BIT(MINBUCKETSLOG2)
/* Compute the maximum entries given n buckets that we will tolerate, ~90% */
#define OVERLOADED(n) ((n) - ((n) >> 3))
/* Compute the number of entries below which we shrink the table by half */
#define UNDERLOADED(n) (((n) > MINBUCKETS) ? ((n) >> 2) : 0)
/*
** Stubs for default hash allocator ops.
*/
static void *
DefaultAllocTable(void *pool, size_t size)
{
return js_malloc(size);
}
static void
DefaultFreeTable(void *pool, void *item, size_t size)
{
js_free(item);
}
static JSHashEntry *
DefaultAllocEntry(void *pool, const void *key)
{
return (JSHashEntry*) js_malloc(sizeof(JSHashEntry));
}
static void
DefaultFreeEntry(void *pool, JSHashEntry *he, unsigned flag)
{
if (flag == HT_FREE_ENTRY)
js_free(he);
}
static const JSHashAllocOps defaultHashAllocOps = {
DefaultAllocTable, DefaultFreeTable,
DefaultAllocEntry, DefaultFreeEntry
};
JSHashTable *
JS_NewHashTable(uint32_t n, JSHashFunction keyHash,
JSHashComparator keyCompare, JSHashComparator valueCompare,
const JSHashAllocOps *allocOps, void *allocPriv)
{
JSHashTable *ht;
size_t nb;
if (n <= MINBUCKETS) {
n = MINBUCKETSLOG2;
} else {
n = CeilingLog2Size(n);
if (int32_t(n) < 0)
return nullptr;
}
if (!allocOps) allocOps = &defaultHashAllocOps;
ht = (JSHashTable*) allocOps->allocTable(allocPriv, sizeof *ht);
if (!ht)
return nullptr;
memset(ht, 0, sizeof *ht);
ht->shift = JS_HASH_BITS - n;
n = JS_BIT(n);
nb = n * sizeof(JSHashEntry *);
ht->buckets = (JSHashEntry**) allocOps->allocTable(allocPriv, nb);
if (!ht->buckets) {
allocOps->freeTable(allocPriv, ht, nb);
return nullptr;
}
memset(ht->buckets, 0, nb);
ht->keyHash = keyHash;
ht->keyCompare = keyCompare;
ht->valueCompare = valueCompare;
ht->allocOps = allocOps;
ht->allocPriv = allocPriv;
return ht;
}
void
JS_HashTableDestroy(JSHashTable *ht)
{
uint32_t i, n;
JSHashEntry *he, **hep;
const JSHashAllocOps *allocOps = ht->allocOps;
void *allocPriv = ht->allocPriv;
n = NBUCKETS(ht);
for (i = 0; i < n; i++) {
hep = &ht->buckets[i];
while ((he = *hep) != nullptr) {
*hep = he->next;
allocOps->freeEntry(allocPriv, he, HT_FREE_ENTRY);
}
}
#ifdef DEBUG
memset(ht->buckets, 0xDB, n * sizeof ht->buckets[0]);
#endif
allocOps->freeTable(allocPriv, ht->buckets, n * sizeof ht->buckets[0]);
#ifdef DEBUG
memset(ht, 0xDB, sizeof *ht);
#endif
allocOps->freeTable(allocPriv, ht, sizeof *ht);
}
/*
* Multiplicative hash, from Knuth 6.4.
*/
#define BUCKET_HEAD(ht, keyHash) \
(&(ht)->buckets[((keyHash) * JS_GOLDEN_RATIO) >> (ht)->shift])
JSHashEntry **
JS_HashTableRawLookup(JSHashTable *ht, JSHashNumber keyHash, const void *key)
{
JSHashEntry *he, **hep, **hep0;
#ifdef JS_HASHMETER
ht->nlookups++;
#endif
hep = hep0 = BUCKET_HEAD(ht, keyHash);
while ((he = *hep) != nullptr) {
if (he->keyHash == keyHash && ht->keyCompare(key, he->key)) {
/* Move to front of chain if not already there */
if (hep != hep0) {
*hep = he->next;
he->next = *hep0;
*hep0 = he;
}
return hep0;
}
hep = &he->next;
#ifdef JS_HASHMETER
ht->nsteps++;
#endif
}
return hep;
}
static bool
Resize(JSHashTable *ht, uint32_t newshift)
{
size_t nb, nentries, i;
JSHashEntry **oldbuckets, *he, *next, **hep;
size_t nold = NBUCKETS(ht);
MOZ_ASSERT(newshift < JS_HASH_BITS);
nb = (size_t)1 << (JS_HASH_BITS - newshift);
/* Integer overflow protection. */
if (nb > (size_t)-1 / sizeof(JSHashEntry*))
return false;
nb *= sizeof(JSHashEntry*);
oldbuckets = ht->buckets;
ht->buckets = (JSHashEntry**)ht->allocOps->allocTable(ht->allocPriv, nb);
if (!ht->buckets) {
ht->buckets = oldbuckets;
return false;
}
memset(ht->buckets, 0, nb);
ht->shift = newshift;
nentries = ht->nentries;
for (i = 0; nentries != 0; i++) {
for (he = oldbuckets[i]; he; he = next) {
MOZ_ASSERT(nentries != 0);
--nentries;
next = he->next;
hep = BUCKET_HEAD(ht, he->keyHash);
/*
* We do not require unique entries, instead appending he to the
* chain starting at hep.
*/
while (*hep)
hep = &(*hep)->next;
he->next = nullptr;
*hep = he;
}
}
#ifdef DEBUG
memset(oldbuckets, 0xDB, nold * sizeof oldbuckets[0]);
#endif
ht->allocOps->freeTable(ht->allocPriv, oldbuckets,
nold * sizeof oldbuckets[0]);
return true;
}
JSHashEntry *
JS_HashTableRawAdd(JSHashTable *ht, JSHashEntry **&hep,
JSHashNumber keyHash, const void *key, void *value)
{
uint32_t n;
JSHashEntry *he;
/* Grow the table if it is overloaded */
n = NBUCKETS(ht);
if (ht->nentries >= OVERLOADED(n)) {
if (!Resize(ht, ht->shift - 1))
return nullptr;
#ifdef JS_HASHMETER
ht->ngrows++;
#endif
hep = JS_HashTableRawLookup(ht, keyHash, key);
}
/* Make a new key value entry */
he = ht->allocOps->allocEntry(ht->allocPriv, key);
if (!he)
return nullptr;
he->keyHash = keyHash;
he->key = key;
he->value = value;
he->next = *hep;
*hep = he;
ht->nentries++;
return he;
}
JSHashEntry *
JS_HashTableAdd(JSHashTable *ht, const void *key, void *value)
{
JSHashNumber keyHash;
JSHashEntry *he, **hep;
keyHash = ht->keyHash(key);
hep = JS_HashTableRawLookup(ht, keyHash, key);
if ((he = *hep) != nullptr) {
/* Hit; see if values match */
if (ht->valueCompare(he->value, value)) {
/* key,value pair is already present in table */
return he;
}
if (he->value)
ht->allocOps->freeEntry(ht->allocPriv, he, HT_FREE_VALUE);
he->value = value;
return he;
}
return JS_HashTableRawAdd(ht, hep, keyHash, key, value);
}
void
JS_HashTableRawRemove(JSHashTable *ht, JSHashEntry **hep, JSHashEntry *he)
{
uint32_t n;
*hep = he->next;
ht->allocOps->freeEntry(ht->allocPriv, he, HT_FREE_ENTRY);
/* Shrink table if it's underloaded */
n = NBUCKETS(ht);
if (--ht->nentries < UNDERLOADED(n)) {
Resize(ht, ht->shift + 1);
#ifdef JS_HASHMETER
ht->nshrinks++;
#endif
}
}
bool
JS_HashTableRemove(JSHashTable *ht, const void *key)
{
JSHashNumber keyHash;
JSHashEntry *he, **hep;
keyHash = ht->keyHash(key);
hep = JS_HashTableRawLookup(ht, keyHash, key);
if ((he = *hep) == nullptr)
return false;
/* Hit; remove element */
JS_HashTableRawRemove(ht, hep, he);
return true;
}
void *
JS_HashTableLookup(JSHashTable *ht, const void *key)
{
JSHashNumber keyHash;
JSHashEntry *he, **hep;
keyHash = ht->keyHash(key);
hep = JS_HashTableRawLookup(ht, keyHash, key);
if ((he = *hep) != nullptr) {
return he->value;
}
return nullptr;
}
/*
** Iterate over the entries in the hash table calling func for each
** entry found. Stop if "f" says to (return value & JS_ENUMERATE_STOP).
** Return a count of the number of elements scanned.
*/
int
JS_HashTableEnumerateEntries(JSHashTable *ht, JSHashEnumerator f, void *arg)
{
JSHashEntry *he, **hep, **bucket;
uint32_t nlimit, n, nbuckets, newlog2;
int rv;
nlimit = ht->nentries;
n = 0;
for (bucket = ht->buckets; n != nlimit; ++bucket) {
hep = bucket;
while ((he = *hep) != nullptr) {
MOZ_ASSERT(n < nlimit);
rv = f(he, n, arg);
n++;
if (rv & HT_ENUMERATE_REMOVE) {
*hep = he->next;
ht->allocOps->freeEntry(ht->allocPriv, he, HT_FREE_ENTRY);
--ht->nentries;
} else {
hep = &he->next;
}
if (rv & HT_ENUMERATE_STOP) {
goto out;
}
}
}
out:
/* Shrink table if removal of entries made it underloaded */
if (ht->nentries != nlimit) {
MOZ_ASSERT(ht->nentries < nlimit);
nbuckets = NBUCKETS(ht);
if (MINBUCKETS < nbuckets && ht->nentries < UNDERLOADED(nbuckets)) {
newlog2 = CeilingLog2Size(ht->nentries);
if (newlog2 < MINBUCKETSLOG2)
newlog2 = MINBUCKETSLOG2;
/* Check that we really shrink the table. */
MOZ_ASSERT(JS_HASH_BITS - ht->shift > newlog2);
Resize(ht, JS_HASH_BITS - newlog2);
}
}
return (int)n;
}
#ifdef JS_HASHMETER
#include <stdio.h>
void
JS_HashTableDumpMeter(JSHashTable *ht, JSHashEnumerator dump, FILE *fp)
{
double sqsum, mean, sigma;
uint32_t nchains, nbuckets;
uint32_t i, n, maxChain, maxChainLen;
JSHashEntry *he;
sqsum = 0;
nchains = 0;
maxChain = maxChainLen = 0;
nbuckets = NBUCKETS(ht);
for (i = 0; i < nbuckets; i++) {
he = ht->buckets[i];
if (!he)
continue;
nchains++;
for (n = 0; he; he = he->next)
n++;
sqsum += n * n;
if (n > maxChainLen) {
maxChainLen = n;
maxChain = i;
}
}
mean = JS_MeanAndStdDev(nchains, ht->nentries, sqsum, &sigma);
fprintf(fp, "\nHash table statistics:\n");
fprintf(fp, " number of lookups: %u\n", ht->nlookups);
fprintf(fp, " number of entries: %u\n", ht->nentries);
fprintf(fp, " number of grows: %u\n", ht->ngrows);
fprintf(fp, " number of shrinks: %u\n", ht->nshrinks);
fprintf(fp, " mean steps per hash: %g\n", (double)ht->nsteps
/ ht->nlookups);
fprintf(fp, "mean hash chain length: %g\n", mean);
fprintf(fp, " standard deviation: %g\n", sigma);
fprintf(fp, " max hash chain length: %u\n", maxChainLen);
fprintf(fp, " max hash chain: [%u]\n", maxChain);
for (he = ht->buckets[maxChain], i = 0; he; he = he->next, i++)
if (dump(he, i, fp) != HT_ENUMERATE_NEXT)
break;
}
#endif /* JS_HASHMETER */
int
JS_HashTableDump(JSHashTable *ht, JSHashEnumerator dump, FILE *fp)
{
int count;
count = JS_HashTableEnumerateEntries(ht, dump, fp);
#ifdef JS_HASHMETER
JS_HashTableDumpMeter(ht, dump, fp);
#endif
return count;
}
JSHashNumber
JS_HashString(const void *key)
{
JSHashNumber h;
const unsigned char *s;
h = 0;
for (s = (const unsigned char *)key; *s; s++)
h = RotateLeft(h, 4) ^ *s;
return h;
}
int
JS_CompareValues(const void *v1, const void *v2)
{
return v1 == v2;
}
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