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gecko-dev/xpcom/glue/pldhash.cpp

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/* -*- Mode: C; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
/* 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/. */
/*
* Double hashing implementation.
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "pldhash.h"
#include "mozilla/HashFunctions.h"
#include "mozilla/MathAlgorithms.h"
#include "nsDebug.h" /* for PR_ASSERT */
#include "nsAlgorithm.h"
#include "mozilla/Likely.h"
#include "mozilla/MemoryReporting.h"
#ifdef PL_DHASHMETER
# define METER(x) x
#else
# define METER(x) /* nothing */
#endif
/*
* The following DEBUG-only code is used to assert that calls to one of
* table->ops or to an enumerator do not cause re-entry into a call that
* can mutate the table.
*/
#ifdef DEBUG
/*
* Most callers that assert about the recursion level don't care about
* this magical value because they are asserting that mutation is
* allowed (and therefore the level is 0 or 1, depending on whether they
* incremented it).
*
* Only PL_DHashTableFinish needs to allow this special value.
*/
#define IMMUTABLE_RECURSION_LEVEL ((uint16_t)-1)
#define RECURSION_LEVEL_SAFE_TO_FINISH(table_) \
(table_->recursionLevel == 0 || \
table_->recursionLevel == IMMUTABLE_RECURSION_LEVEL)
#define INCREMENT_RECURSION_LEVEL(table_) \
do { \
if (table_->recursionLevel != IMMUTABLE_RECURSION_LEVEL) \
++table_->recursionLevel; \
} while(0)
#define DECREMENT_RECURSION_LEVEL(table_) \
do { \
if (table->recursionLevel != IMMUTABLE_RECURSION_LEVEL) { \
MOZ_ASSERT(table->recursionLevel > 0); \
--table->recursionLevel; \
} \
} while(0)
#else
#define INCREMENT_RECURSION_LEVEL(table_) do { } while(0)
#define DECREMENT_RECURSION_LEVEL(table_) do { } while(0)
#endif /* defined(DEBUG) */
using namespace mozilla;
void *
PL_DHashAllocTable(PLDHashTable *table, uint32_t nbytes)
{
return malloc(nbytes);
}
void
PL_DHashFreeTable(PLDHashTable *table, void *ptr)
{
free(ptr);
}
PLDHashNumber
PL_DHashStringKey(PLDHashTable *table, const void *key)
{
return HashString(static_cast<const char*>(key));
}
PLDHashNumber
PL_DHashVoidPtrKeyStub(PLDHashTable *table, const void *key)
{
return (PLDHashNumber)(ptrdiff_t)key >> 2;
}
bool
PL_DHashMatchEntryStub(PLDHashTable *table,
const PLDHashEntryHdr *entry,
const void *key)
{
const PLDHashEntryStub *stub = (const PLDHashEntryStub *)entry;
return stub->key == key;
}
bool
PL_DHashMatchStringKey(PLDHashTable *table,
const PLDHashEntryHdr *entry,
const void *key)
{
const PLDHashEntryStub *stub = (const PLDHashEntryStub *)entry;
/* XXX tolerate null keys on account of sloppy Mozilla callers. */
return stub->key == key ||
(stub->key && key &&
strcmp((const char *) stub->key, (const char *) key) == 0);
}
void
PL_DHashMoveEntryStub(PLDHashTable *table,
const PLDHashEntryHdr *from,
PLDHashEntryHdr *to)
{
memcpy(to, from, table->entrySize);
}
void
PL_DHashClearEntryStub(PLDHashTable *table, PLDHashEntryHdr *entry)
{
memset(entry, 0, table->entrySize);
}
void
PL_DHashFreeStringKey(PLDHashTable *table, PLDHashEntryHdr *entry)
{
const PLDHashEntryStub *stub = (const PLDHashEntryStub *)entry;
free((void *) stub->key);
memset(entry, 0, table->entrySize);
}
void
PL_DHashFinalizeStub(PLDHashTable *table)
{
}
static const PLDHashTableOps stub_ops = {
PL_DHashAllocTable,
PL_DHashFreeTable,
PL_DHashVoidPtrKeyStub,
PL_DHashMatchEntryStub,
PL_DHashMoveEntryStub,
PL_DHashClearEntryStub,
PL_DHashFinalizeStub,
nullptr
};
const PLDHashTableOps *
PL_DHashGetStubOps(void)
{
return &stub_ops;
}
static bool
SizeOfEntryStore(uint32_t capacity, uint32_t entrySize, uint32_t *nbytes)
{
uint64_t nbytes64 = uint64_t(capacity) * uint64_t(entrySize);
*nbytes = capacity * entrySize;
return uint64_t(*nbytes) == nbytes64; // returns false on overflow
}
PLDHashTable *
PL_NewDHashTable(const PLDHashTableOps *ops, void *data, uint32_t entrySize,
uint32_t capacity)
{
PLDHashTable *table = (PLDHashTable *) malloc(sizeof *table);
if (!table)
return nullptr;
if (!PL_DHashTableInit(table, ops, data, entrySize, capacity)) {
free(table);
return nullptr;
}
return table;
}
void
PL_DHashTableDestroy(PLDHashTable *table)
{
PL_DHashTableFinish(table);
free(table);
}
bool
PL_DHashTableInit(PLDHashTable *table, const PLDHashTableOps *ops, void *data,
uint32_t entrySize, uint32_t capacity)
{
#ifdef DEBUG
if (entrySize > 16 * sizeof(void *)) {
printf_stderr(
"pldhash: for the table at address %p, the given entrySize"
" of %lu definitely favors chaining over double hashing.\n",
(void *) table,
(unsigned long) entrySize);
}
#endif
table->ops = ops;
table->data = data;
if (capacity < PL_DHASH_MIN_SIZE)
capacity = PL_DHASH_MIN_SIZE;
int log2 = CeilingLog2(capacity);
capacity = 1u << log2;
if (capacity > PL_DHASH_MAX_SIZE)
return false;
table->hashShift = PL_DHASH_BITS - log2;
table->entrySize = entrySize;
table->entryCount = table->removedCount = 0;
table->generation = 0;
uint32_t nbytes;
if (!SizeOfEntryStore(capacity, entrySize, &nbytes))
return false; // overflowed
table->entryStore = (char *) ops->allocTable(table, nbytes);
if (!table->entryStore)
return false;
memset(table->entryStore, 0, nbytes);
METER(memset(&table->stats, 0, sizeof table->stats));
#ifdef DEBUG
table->recursionLevel = 0;
#endif
return true;
}
/*
* Compute max and min load numbers (entry counts). We have a secondary max
* that allows us to overload a table reasonably if it cannot be grown further
* (i.e. if ChangeTable() fails). The table slows down drastically if the
* secondary max is too close to 1, but 0.96875 gives only a slight slowdown
* while allowing 1.3x more elements.
*/
static inline uint32_t MaxLoad(uint32_t size) {
return size - (size >> 2); // == size * 0.75
}
static inline uint32_t MaxLoadOnGrowthFailure(uint32_t size) {
return size - (size >> 5); // == size * 0.96875
}
static inline uint32_t MinLoad(uint32_t size) {
return size >> 2; // == size * 0.25
}
/*
* 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 PL_DHASH_ENTRY_IS_LIVE
* in pldhash.h. It used to be private to pldhash.c, but then became public to
* assist iterator writers who inspect table->entryStore directly.
*/
#define COLLISION_FLAG ((PLDHashNumber) 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) PL_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) \
((PLDHashEntryHdr *)((table)->entryStore + (index) * (table)->entrySize))
void
PL_DHashTableFinish(PLDHashTable *table)
{
INCREMENT_RECURSION_LEVEL(table);
/* Call finalize before clearing entries, so it can enumerate them. */
table->ops->finalize(table);
/* Clear any remaining live entries. */
char *entryAddr = table->entryStore;
uint32_t entrySize = table->entrySize;
char *entryLimit = entryAddr + PL_DHASH_TABLE_SIZE(table) * entrySize;
while (entryAddr < entryLimit) {
PLDHashEntryHdr *entry = (PLDHashEntryHdr *)entryAddr;
if (ENTRY_IS_LIVE(entry)) {
METER(table->stats.removeEnums++);
table->ops->clearEntry(table, entry);
}
entryAddr += entrySize;
}
DECREMENT_RECURSION_LEVEL(table);
MOZ_ASSERT(RECURSION_LEVEL_SAFE_TO_FINISH(table));
/* Free entry storage last. */
table->ops->freeTable(table, table->entryStore);
}
static PLDHashEntryHdr * PL_DHASH_FASTCALL
SearchTable(PLDHashTable *table, const void *key, PLDHashNumber keyHash,
PLDHashOperator op)
{
METER(table->stats.searches++);
NS_ASSERTION(!(keyHash & COLLISION_FLAG),
"!(keyHash & COLLISION_FLAG)");
/* Compute the primary hash address. */
int hashShift = table->hashShift;
PLDHashNumber hash1 = HASH1(keyHash, hashShift);
PLDHashEntryHdr *entry = ADDRESS_ENTRY(table, hash1);
/* Miss: return space for a new entry. */
if (PL_DHASH_ENTRY_IS_FREE(entry)) {
METER(table->stats.misses++);
return entry;
}
/* Hit: return entry. */
PLDHashMatchEntry matchEntry = table->ops->matchEntry;
if (MATCH_ENTRY_KEYHASH(entry, keyHash) && matchEntry(table, entry, key)) {
METER(table->stats.hits++);
return entry;
}
/* Collision: double hash. */
int sizeLog2 = PL_DHASH_BITS - table->hashShift;
PLDHashNumber hash2 = HASH2(keyHash, sizeLog2, hashShift);
uint32_t sizeMask = (1u << sizeLog2) - 1;
/* Save the first removed entry pointer so PL_DHASH_ADD can recycle it. */
PLDHashEntryHdr *firstRemoved = nullptr;
for (;;) {
if (MOZ_UNLIKELY(ENTRY_IS_REMOVED(entry))) {
if (!firstRemoved)
firstRemoved = entry;
} else {
if (op == PL_DHASH_ADD)
entry->keyHash |= COLLISION_FLAG;
}
METER(table->stats.steps++);
hash1 -= hash2;
hash1 &= sizeMask;
entry = ADDRESS_ENTRY(table, hash1);
if (PL_DHASH_ENTRY_IS_FREE(entry)) {
METER(table->stats.misses++);
return (firstRemoved && op == PL_DHASH_ADD) ? firstRemoved : entry;
}
if (MATCH_ENTRY_KEYHASH(entry, keyHash) &&
matchEntry(table, entry, key)) {
METER(table->stats.hits++);
return entry;
}
}
/* NOTREACHED */
return nullptr;
}
/*
* This is a copy of SearchTable, used by ChangeTable, hardcoded to
* 1. assume |op == PL_DHASH_ADD|,
* 2. assume that |key| will never match an existing entry, and
* 3. assume that no entries have been removed from the current table
* structure.
* Avoiding the need for |key| means we can avoid needing a way to map
* entries to keys, which means callers can use complex key types more
* easily.
*/
static PLDHashEntryHdr * PL_DHASH_FASTCALL
FindFreeEntry(PLDHashTable *table, PLDHashNumber keyHash)
{
METER(table->stats.searches++);
NS_ASSERTION(!(keyHash & COLLISION_FLAG),
"!(keyHash & COLLISION_FLAG)");
/* Compute the primary hash address. */
int hashShift = table->hashShift;
PLDHashNumber hash1 = HASH1(keyHash, hashShift);
PLDHashEntryHdr *entry = ADDRESS_ENTRY(table, hash1);
/* Miss: return space for a new entry. */
if (PL_DHASH_ENTRY_IS_FREE(entry)) {
METER(table->stats.misses++);
return entry;
}
/* Collision: double hash. */
int sizeLog2 = PL_DHASH_BITS - table->hashShift;
PLDHashNumber hash2 = HASH2(keyHash, sizeLog2, hashShift);
uint32_t sizeMask = (1u << sizeLog2) - 1;
for (;;) {
NS_ASSERTION(!ENTRY_IS_REMOVED(entry),
"!ENTRY_IS_REMOVED(entry)");
entry->keyHash |= COLLISION_FLAG;
METER(table->stats.steps++);
hash1 -= hash2;
hash1 &= sizeMask;
entry = ADDRESS_ENTRY(table, hash1);
if (PL_DHASH_ENTRY_IS_FREE(entry)) {
METER(table->stats.misses++);
return entry;
}
}
/* NOTREACHED */
return nullptr;
}
static bool
ChangeTable(PLDHashTable *table, int deltaLog2)
{
/* Look, but don't touch, until we succeed in getting new entry store. */
int oldLog2 = PL_DHASH_BITS - table->hashShift;
int newLog2 = oldLog2 + deltaLog2;
uint32_t newCapacity = 1u << newLog2;
if (newCapacity > PL_DHASH_MAX_SIZE)
return false;
uint32_t entrySize = table->entrySize;
uint32_t nbytes;
if (!SizeOfEntryStore(newCapacity, entrySize, &nbytes))
return false; // overflowed
char *newEntryStore = (char *) table->ops->allocTable(table, nbytes);
if (!newEntryStore)
return false;
/* We can't fail from here on, so update table parameters. */
#ifdef DEBUG
uint32_t recursionLevel = table->recursionLevel;
#endif
table->hashShift = PL_DHASH_BITS - newLog2;
table->removedCount = 0;
table->generation++;
/* Assign the new entry store to table. */
memset(newEntryStore, 0, nbytes);
char *oldEntryStore, *oldEntryAddr;
oldEntryAddr = oldEntryStore = table->entryStore;
table->entryStore = newEntryStore;
PLDHashMoveEntry moveEntry = table->ops->moveEntry;
#ifdef DEBUG
table->recursionLevel = recursionLevel;
#endif
/* Copy only live entries, leaving removed ones behind. */
uint32_t oldCapacity = 1u << oldLog2;
for (uint32_t i = 0; i < oldCapacity; i++) {
PLDHashEntryHdr *oldEntry = (PLDHashEntryHdr *)oldEntryAddr;
if (ENTRY_IS_LIVE(oldEntry)) {
oldEntry->keyHash &= ~COLLISION_FLAG;
PLDHashEntryHdr *newEntry = FindFreeEntry(table, oldEntry->keyHash);
NS_ASSERTION(PL_DHASH_ENTRY_IS_FREE(newEntry),
"PL_DHASH_ENTRY_IS_FREE(newEntry)");
moveEntry(table, oldEntry, newEntry);
newEntry->keyHash = oldEntry->keyHash;
}
oldEntryAddr += entrySize;
}
table->ops->freeTable(table, oldEntryStore);
return true;
}
PLDHashEntryHdr * PL_DHASH_FASTCALL
PL_DHashTableOperate(PLDHashTable *table, const void *key, PLDHashOperator op)
{
PLDHashEntryHdr *entry;
MOZ_ASSERT(op == PL_DHASH_LOOKUP || table->recursionLevel == 0);
INCREMENT_RECURSION_LEVEL(table);
PLDHashNumber keyHash = table->ops->hashKey(table, key);
keyHash *= PL_DHASH_GOLDEN_RATIO;
/* Avoid 0 and 1 hash codes, they indicate free and removed entries. */
ENSURE_LIVE_KEYHASH(keyHash);
keyHash &= ~COLLISION_FLAG;
switch (op) {
case PL_DHASH_LOOKUP:
METER(table->stats.lookups++);
entry = SearchTable(table, key, keyHash, op);
break;
case PL_DHASH_ADD: {
/*
* If alpha is >= .75, grow or compress the table. If key is already
* in the table, we may grow once more than necessary, but only if we
* are on the edge of being overloaded.
*/
uint32_t size = PL_DHASH_TABLE_SIZE(table);
if (table->entryCount + table->removedCount >= MaxLoad(size)) {
/* Compress if a quarter or more of all entries are removed. */
int deltaLog2;
if (table->removedCount >= size >> 2) {
METER(table->stats.compresses++);
deltaLog2 = 0;
} else {
METER(table->stats.grows++);
deltaLog2 = 1;
}
/*
* Grow or compress table. If ChangeTable() fails, allow
* overloading up to the secondary max. Once we hit the secondary
* max, return null.
*/
if (!ChangeTable(table, deltaLog2) &&
table->entryCount + table->removedCount >=
MaxLoadOnGrowthFailure(size))
{
METER(table->stats.addFailures++);
entry = nullptr;
break;
}
}
/*
* Look for entry after possibly growing, so we don't have to add it,
* then skip it while growing the table and re-add it after.
*/
entry = SearchTable(table, key, keyHash, op);
if (!ENTRY_IS_LIVE(entry)) {
/* Initialize the entry, indicating that it's no longer free. */
METER(table->stats.addMisses++);
if (ENTRY_IS_REMOVED(entry)) {
METER(table->stats.addOverRemoved++);
table->removedCount--;
keyHash |= COLLISION_FLAG;
}
if (table->ops->initEntry &&
!table->ops->initEntry(table, entry, key)) {
/* We haven't claimed entry yet; fail with null return. */
memset(entry + 1, 0, table->entrySize - sizeof *entry);
entry = nullptr;
break;
}
entry->keyHash = keyHash;
table->entryCount++;
}
METER(else table->stats.addHits++);
break;
}
case PL_DHASH_REMOVE:
entry = SearchTable(table, key, keyHash, op);
if (ENTRY_IS_LIVE(entry)) {
/* Clear this entry and mark it as "removed". */
METER(table->stats.removeHits++);
PL_DHashTableRawRemove(table, entry);
/* Shrink if alpha is <= .25 and table isn't too small already. */
uint32_t size = PL_DHASH_TABLE_SIZE(table);
if (size > PL_DHASH_MIN_SIZE &&
table->entryCount <= MinLoad(size)) {
METER(table->stats.shrinks++);
(void) ChangeTable(table, -1);
}
}
METER(else table->stats.removeMisses++);
entry = nullptr;
break;
default:
NS_NOTREACHED("0");
entry = nullptr;
}
DECREMENT_RECURSION_LEVEL(table);
return entry;
}
void
PL_DHashTableRawRemove(PLDHashTable *table, PLDHashEntryHdr *entry)
{
MOZ_ASSERT(table->recursionLevel != IMMUTABLE_RECURSION_LEVEL);
NS_ASSERTION(PL_DHASH_ENTRY_IS_LIVE(entry),
"PL_DHASH_ENTRY_IS_LIVE(entry)");
/* Load keyHash first in case clearEntry() goofs it. */
PLDHashNumber keyHash = entry->keyHash;
table->ops->clearEntry(table, entry);
if (keyHash & COLLISION_FLAG) {
MARK_ENTRY_REMOVED(entry);
table->removedCount++;
} else {
METER(table->stats.removeFrees++);
MARK_ENTRY_FREE(entry);
}
table->entryCount--;
}
uint32_t
PL_DHashTableEnumerate(PLDHashTable *table, PLDHashEnumerator etor, void *arg)
{
INCREMENT_RECURSION_LEVEL(table);
char *entryAddr = table->entryStore;
uint32_t entrySize = table->entrySize;
uint32_t capacity = PL_DHASH_TABLE_SIZE(table);
char *entryLimit = entryAddr + capacity * entrySize;
uint32_t i = 0;
bool didRemove = false;
while (entryAddr < entryLimit) {
PLDHashEntryHdr *entry = (PLDHashEntryHdr *)entryAddr;
if (ENTRY_IS_LIVE(entry)) {
PLDHashOperator op = etor(table, entry, i++, arg);
if (op & PL_DHASH_REMOVE) {
METER(table->stats.removeEnums++);
PL_DHashTableRawRemove(table, entry);
didRemove = true;
}
if (op & PL_DHASH_STOP)
break;
}
entryAddr += entrySize;
}
MOZ_ASSERT(!didRemove || table->recursionLevel == 1);
/*
* Shrink or compress if a quarter or more of all entries are removed, or
* if the table is underloaded according to the minimum alpha, and is not
* minimal-size already. Do this only if we removed above, so non-removing
* enumerations can count on stable table->entryStore until the next
* non-lookup-Operate or removing-Enumerate.
*/
if (didRemove &&
(table->removedCount >= capacity >> 2 ||
(capacity > PL_DHASH_MIN_SIZE &&
table->entryCount <= MinLoad(capacity)))) {
METER(table->stats.enumShrinks++);
capacity = table->entryCount;
capacity += capacity >> 1;
if (capacity < PL_DHASH_MIN_SIZE)
capacity = PL_DHASH_MIN_SIZE;
uint32_t ceiling = CeilingLog2(capacity);
ceiling -= PL_DHASH_BITS - table->hashShift;
(void) ChangeTable(table, ceiling);
}
DECREMENT_RECURSION_LEVEL(table);
return i;
}
struct SizeOfEntryExcludingThisArg
{
size_t total;
PLDHashSizeOfEntryExcludingThisFun sizeOfEntryExcludingThis;
MallocSizeOf mallocSizeOf;
void *arg; // the arg passed by the user
};
static PLDHashOperator
SizeOfEntryExcludingThisEnumerator(PLDHashTable *table, PLDHashEntryHdr *hdr,
uint32_t number, void *arg)
{
SizeOfEntryExcludingThisArg *e = (SizeOfEntryExcludingThisArg *)arg;
e->total += e->sizeOfEntryExcludingThis(hdr, e->mallocSizeOf, e->arg);
return PL_DHASH_NEXT;
}
size_t
PL_DHashTableSizeOfExcludingThis(const PLDHashTable *table,
PLDHashSizeOfEntryExcludingThisFun sizeOfEntryExcludingThis,
MallocSizeOf mallocSizeOf,
void *arg /* = nullptr */)
{
size_t n = 0;
n += mallocSizeOf(table->entryStore);
if (sizeOfEntryExcludingThis) {
SizeOfEntryExcludingThisArg arg2 = { 0, sizeOfEntryExcludingThis, mallocSizeOf, arg };
PL_DHashTableEnumerate(const_cast<PLDHashTable *>(table),
SizeOfEntryExcludingThisEnumerator, &arg2);
n += arg2.total;
}
return n;
}
size_t
PL_DHashTableSizeOfIncludingThis(const PLDHashTable *table,
PLDHashSizeOfEntryExcludingThisFun sizeOfEntryExcludingThis,
MallocSizeOf mallocSizeOf,
void *arg /* = nullptr */)
{
return mallocSizeOf(table) +
PL_DHashTableSizeOfExcludingThis(table, sizeOfEntryExcludingThis,
mallocSizeOf, arg);
}
#ifdef DEBUG
void
PL_DHashMarkTableImmutable(PLDHashTable *table)
{
table->recursionLevel = IMMUTABLE_RECURSION_LEVEL;
}
#endif
#ifdef PL_DHASHMETER
#include <math.h>
void
PL_DHashTableDumpMeter(PLDHashTable *table, PLDHashEnumerator dump, FILE *fp)
{
PLDHashNumber hash1, hash2, maxChainHash1, maxChainHash2;
double sqsum, mean, variance, sigma;
PLDHashEntryHdr *entry;
char *entryAddr = table->entryStore;
uint32_t entrySize = table->entrySize;
int hashShift = table->hashShift;
int sizeLog2 = PL_DHASH_BITS - hashShift;
uint32_t tableSize = PL_DHASH_TABLE_SIZE(table);
uint32_t sizeMask = (1u << sizeLog2) - 1;
uint32_t chainCount = 0, maxChainLen = 0;
hash2 = 0;
sqsum = 0;
for (uint32_t i = 0; i < tableSize; i++) {
entry = (PLDHashEntryHdr *)entryAddr;
entryAddr += entrySize;
if (!ENTRY_IS_LIVE(entry))
continue;
hash1 = HASH1(entry->keyHash & ~COLLISION_FLAG, hashShift);
PLDHashNumber saveHash1 = hash1;
PLDHashEntryHdr *probe = ADDRESS_ENTRY(table, hash1);
uint32_t chainLen = 1;
if (probe == entry) {
/* Start of a (possibly unit-length) chain. */
chainCount++;
} else {
hash2 = HASH2(entry->keyHash & ~COLLISION_FLAG, sizeLog2,
hashShift);
do {
chainLen++;
hash1 -= hash2;
hash1 &= sizeMask;
probe = ADDRESS_ENTRY(table, hash1);
} while (probe != entry);
}
sqsum += chainLen * chainLen;
if (chainLen > maxChainLen) {
maxChainLen = chainLen;
maxChainHash1 = saveHash1;
maxChainHash2 = hash2;
}
}
uint32_t entryCount = table->entryCount;
if (entryCount && chainCount) {
mean = (double)entryCount / chainCount;
variance = chainCount * sqsum - entryCount * entryCount;
if (variance < 0 || chainCount == 1)
variance = 0;
else
variance /= chainCount * (chainCount - 1);
sigma = sqrt(variance);
} else {
mean = sigma = 0;
}
fprintf(fp, "Double hashing statistics:\n");
fprintf(fp, " table size (in entries): %u\n", tableSize);
fprintf(fp, " number of entries: %u\n", table->entryCount);
fprintf(fp, " number of removed entries: %u\n", table->removedCount);
fprintf(fp, " number of searches: %u\n", table->stats.searches);
fprintf(fp, " number of hits: %u\n", table->stats.hits);
fprintf(fp, " number of misses: %u\n", table->stats.misses);
fprintf(fp, " mean steps per search: %g\n", table->stats.searches ?
(double)table->stats.steps
/ table->stats.searches :
0.);
fprintf(fp, " mean hash chain length: %g\n", mean);
fprintf(fp, " standard deviation: %g\n", sigma);
fprintf(fp, " maximum hash chain length: %u\n", maxChainLen);
fprintf(fp, " number of lookups: %u\n", table->stats.lookups);
fprintf(fp, " adds that made a new entry: %u\n", table->stats.addMisses);
fprintf(fp, "adds that recycled removeds: %u\n", table->stats.addOverRemoved);
fprintf(fp, " adds that found an entry: %u\n", table->stats.addHits);
fprintf(fp, " add failures: %u\n", table->stats.addFailures);
fprintf(fp, " useful removes: %u\n", table->stats.removeHits);
fprintf(fp, " useless removes: %u\n", table->stats.removeMisses);
fprintf(fp, "removes that freed an entry: %u\n", table->stats.removeFrees);
fprintf(fp, " removes while enumerating: %u\n", table->stats.removeEnums);
fprintf(fp, " number of grows: %u\n", table->stats.grows);
fprintf(fp, " number of shrinks: %u\n", table->stats.shrinks);
fprintf(fp, " number of compresses: %u\n", table->stats.compresses);
fprintf(fp, "number of enumerate shrinks: %u\n", table->stats.enumShrinks);
if (dump && maxChainLen && hash2) {
fputs("Maximum hash chain:\n", fp);
hash1 = maxChainHash1;
hash2 = maxChainHash2;
entry = ADDRESS_ENTRY(table, hash1);
uint32_t i = 0;
do {
if (dump(table, entry, i++, fp) != PL_DHASH_NEXT)
break;
hash1 -= hash2;
hash1 &= sizeMask;
entry = ADDRESS_ENTRY(table, hash1);
} while (PL_DHASH_ENTRY_IS_BUSY(entry));
}
}
#endif /* PL_DHASHMETER */
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