// Copyright (c) 2005, Google Inc.
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
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// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
// ---
// Author: Craig Silverstein
//
// A dense hashtable is a particular implementation of
// a hashtable: one that is meant to minimize memory allocation.
// It does this by using an array to store all the data. We
// steal a value from the key space to indicate "empty" array
// elements (ie indices where no item lives) and another to indicate
// "deleted" elements.
//
// (Note it is possible to change the value of the delete key
// on the fly; you can even remove it, though after that point
// the hashtable is insert_only until you set it again. The empty
// value however can't be changed.)
//
// To minimize allocation and pointer overhead, we use internal
// probing, in which the hashtable is a single table, and collisions
// are resolved by trying to insert again in another bucket. The
// most cache-efficient internal probing schemes are linear probing
// (which suffers, alas, from clumping) and quadratic probing, which
// is what we implement by default.
//
// Type requirements: value_type is required to be Copy Constructible
// and Default Constructible. It is not required to be (and commonly
// isn't) Assignable.
//
// You probably shouldn't use this code directly. Use
// <google/dense_hash_map> or <google/dense_hash_set> instead.
// You can change the following below:
// HT_OCCUPANCY_FLT -- how full before we double size
// HT_EMPTY_FLT -- how empty before we halve size
// HT_MIN_BUCKETS -- default smallest bucket size
//
// You can also change enlarge_resize_percent (which defaults to
// HT_OCCUPANCY_FLT), and shrink_resize_percent (which defaults to
// HT_EMPTY_FLT) with set_resizing_parameters().
//
// How to decide what values to use?
// shrink_resize_percent's default of .4 * OCCUPANCY_FLT, is probably good.
// HT_MIN_BUCKETS is probably unnecessary since you can specify
// (indirectly) the starting number of buckets at construct-time.
// For enlarge_resize_percent, you can use this chart to try to trade-off
// expected lookup time to the space taken up. By default, this
// code uses quadratic probing, though you can change it to linear
// via _JUMP below if you really want to.
//
// From http://www.augustana.ca/~mohrj/courses/1999.fall/csc210/lecture_notes/hashing.html
// NUMBER OF PROBES / LOOKUP Successful Unsuccessful
// Quadratic collision resolution 1 - ln(1-L) - L/2 1/(1-L) - L - ln(1-L)
// Linear collision resolution [1+1/(1-L)]/2 [1+1/(1-L)2]/2
//
// -- enlarge_resize_percent -- 0.10 0.50 0.60 0.75 0.80 0.90 0.99
// QUADRATIC COLLISION RES.
// probes/successful lookup 1.05 1.44 1.62 2.01 2.21 2.85 5.11
// probes/unsuccessful lookup 1.11 2.19 2.82 4.64 5.81 11.4 103.6
// LINEAR COLLISION RES.
// probes/successful lookup 1.06 1.5 1.75 2.5 3.0 5.5 50.5
// probes/unsuccessful lookup 1.12 2.5 3.6 8.5 13.0 50.0 5000.0
#ifndef _DENSEHASHTABLE_H_
#define _DENSEHASHTABLE_H_
// The probing method
// Linear probing
// #define JUMP_(key, num_probes) ( 1 )
// Quadratic-ish probing
#define JUMP_(key, num_probes) ( num_probes )
#include <google/sparsehash/sparseconfig.h>
#include <assert.h>
#include <stdio.h>
#include <stdlib.h> // for abort()
#include <algorithm> // For swap(), eg
#include <iostream> // For cerr
#include <memory> // For uninitialized_fill, uninitialized_copy
#include <utility> // for pair<>
#include <iterator> // for facts about iterator tags
#include <google/type_traits.h> // for true_type, integral_constant, etc.
_START_GOOGLE_NAMESPACE_
using STL_NAMESPACE::pair;
// Hashtable class, used to implement the hashed associative containers
// hash_set and hash_map.
// Value: what is stored in the table (each bucket is a Value).
// Key: something in a 1-to-1 correspondence to a Value, that can be used
// to search for a Value in the table (find() takes a Key).
// HashFcn: Takes a Key and returns an integer, the more unique the better.
// ExtractKey: given a Value, returns the unique Key associated with it.
// SetKey: given a Value* and a Key, modifies the value such that
// ExtractKey(value) == key. We guarantee this is only called
// with key == deleted_key or key == empty_key.
// EqualKey: Given two Keys, says whether they are the same (that is,
// if they are both associated with the same Value).
// Alloc: STL allocator to use to allocate memory. Currently ignored.
template <class Value, class Key, class HashFcn,
class ExtractKey, class SetKey, class EqualKey, class Alloc>
class dense_hashtable;
template <class V, class K, class HF, class ExK, class SetK, class EqK, class A>
struct dense_hashtable_iterator;
template <class V, class K, class HF, class ExK, class SetK, class EqK, class A>
struct dense_hashtable_const_iterator;
// We're just an array, but we need to skip over empty and deleted elements
template <class V, class K, class HF, class ExK, class SetK, class EqK, class A>
struct dense_hashtable_iterator {
public:
typedef dense_hashtable_iterator<V,K,HF,ExK,SetK,EqK,A> iterator;
typedef dense_hashtable_const_iterator<V,K,HF,ExK,SetK,EqK,A> const_iterator;
typedef STL_NAMESPACE::forward_iterator_tag iterator_category;
typedef V value_type;
typedef ptrdiff_t difference_type;
typedef size_t size_type;
typedef V& reference; // Value
typedef V* pointer;
// "Real" constructor and default constructor
dense_hashtable_iterator(const dense_hashtable<V,K,HF,ExK,SetK,EqK,A> *h,
pointer it, pointer it_end, bool advance)
: ht(h), pos(it), end(it_end) {
if (advance) advance_past_empty_and_deleted();
}
dense_hashtable_iterator() { }
// The default destructor is fine; we don't define one
// The default operator= is fine; we don't define one
// Happy dereferencer
reference operator*() const { return *pos; }
pointer operator->() const { return &(operator*()); }
// Arithmetic. The only hard part is making sure that
// we're not on an empty or marked-deleted array element
void advance_past_empty_and_deleted() {
while ( pos != end && (ht->test_empty(*this) || ht->test_deleted(*this)) )
++pos;
}
iterator& operator++() {
assert(pos != end); ++pos; advance_past_empty_and_deleted(); return *this;
}
iterator operator++(int) { iterator tmp(*this); ++*this; return tmp; }
// Comparison.
bool operator==(const iterator& it) const { return pos == it.pos; }
bool operator!=(const iterator& it) const { return pos != it.pos; }
// The actual data
const dense_hashtable<V,K,HF,ExK,SetK,EqK,A> *ht;
pointer pos, end;
};
// Now do it all again, but with const-ness!
template <class V, class K, class HF, class ExK, class SetK, class EqK, class A>
struct dense_hashtable_const_iterator {
public:
typedef dense_hashtable_iterator<V,K,HF,ExK,SetK,EqK,A> iterator;
typedef dense_hashtable_const_iterator<V,K,HF,ExK,SetK,EqK,A> const_iterator;
typedef STL_NAMESPACE::forward_iterator_tag iterator_category;
typedef V value_type;
typedef ptrdiff_t difference_type;
typedef size_t size_type;
typedef const V& reference; // Value
typedef const V* pointer;
// "Real" constructor and default constructor
dense_hashtable_const_iterator(
const dense_hashtable<V,K,HF,ExK,SetK,EqK,A> *h,
pointer it, pointer it_end, bool advance)
: ht(h), pos(it), end(it_end) {
if (advance) advance_past_empty_and_deleted();
}
dense_hashtable_const_iterator() { }
// This lets us convert regular iterators to const iterators
dense_hashtable_const_iterator(const iterator &it)
: ht(it.ht), pos(it.pos), end(it.end) { }
// The default destructor is fine; we don't define one
// The default operator= is fine; we don't define one
// Happy dereferencer
reference operator*() const { return *pos; }
pointer operator->() const { return &(operator*()); }
// Arithmetic. The only hard part is making sure that
// we're not on an empty or marked-deleted array element
void advance_past_empty_and_deleted() {
while ( pos != end && (ht->test_empty(*this) || ht->test_deleted(*this)) )
++pos;
}
const_iterator& operator++() {
assert(pos != end); ++pos; advance_past_empty_and_deleted(); return *this;
}
const_iterator operator++(int) { const_iterator tmp(*this); ++*this; return tmp; }
// Comparison.
bool operator==(const const_iterator& it) const { return pos == it.pos; }
bool operator!=(const const_iterator& it) const { return pos != it.pos; }
// The actual data
const dense_hashtable<V,K,HF,ExK,SetK,EqK,A> *ht;
pointer pos, end;
};
template <class Value, class Key, class HashFcn,
class ExtractKey, class SetKey, class EqualKey, class Alloc>
class dense_hashtable {
public:
typedef Key key_type;
typedef Value value_type;
typedef HashFcn hasher;
typedef EqualKey key_equal;
typedef size_t size_type;
typedef ptrdiff_t difference_type;
typedef value_type* pointer;
typedef const value_type* const_pointer;
typedef value_type& reference;
typedef const value_type& const_reference;
typedef dense_hashtable_iterator<Value, Key, HashFcn,
ExtractKey, SetKey, EqualKey, Alloc>
iterator;
typedef dense_hashtable_const_iterator<Value, Key, HashFcn,
ExtractKey, SetKey, EqualKey, Alloc>
const_iterator;
// These come from tr1. For us they're the same as regular iterators.
typedef iterator local_iterator;
typedef const_iterator const_local_iterator;
// How full we let the table get before we resize, by default.
// Knuth says .8 is good -- higher causes us to probe too much,
// though it saves memory.
static const float HT_OCCUPANCY_FLT; // = 0.5;
// How empty we let the table get before we resize lower, by default.
// (0.0 means never resize lower.)
// It should be less than OCCUPANCY_FLT / 2 or we thrash resizing
static const float HT_EMPTY_FLT; // = 0.4 * HT_OCCUPANCY_FLT
// Minimum size we're willing to let hashtables be.
// Must be a power of two, and at least 4.
// Note, however, that for a given hashtable, the initial size is a
// function of the first constructor arg, and may be >HT_MIN_BUCKETS.
static const size_t HT_MIN_BUCKETS = 4;
// By default, if you don't specify a hashtable size at
// construction-time, we use this size. Must be a power of two, and
// at least HT_MIN_BUCKETS.
static const size_t HT_DEFAULT_STARTING_BUCKETS = 32;
// ITERATOR FUNCTIONS
iterator begin() { return iterator(this, table,
table + num_buckets, true); }
iterator end() { return iterator(this, table + num_buckets,
table + num_buckets, true); }
const_iterator begin() const { return const_iterator(this, table,
table+num_buckets,true);}
const_iterator end() const { return const_iterator(this, table + num_buckets,
table+num_buckets,true);}
// These come from tr1 unordered_map. They iterate over 'bucket' n.
// For sparsehashtable, we could consider each 'group' to be a bucket,
// I guess, but I don't really see the point. We'll just consider
// bucket n to be the n-th element of the sparsetable, if it's occupied,
// or some empty element, otherwise.
local_iterator begin(size_type i) {
return local_iterator(this, table + i, table + i+1, false);
}
local_iterator end(size_type i) {
local_iterator it = begin(i);
if (!test_empty(i) && !test_deleted(i))
++it;
return it;
}
const_local_iterator begin(size_type i) const {
return const_local_iterator(this, table + i, table + i+1, false);
}
const_local_iterator end(size_type i) const {
const_local_iterator it = begin(i);
if (!test_empty(i) && !test_deleted(i))
++it;
return it;
}
// ACCESSOR FUNCTIONS for the things we templatize on, basically
hasher hash_funct() const { return hash; }
key_equal key_eq() const { return equals; }
private:
// Annoyingly, we can't copy values around, because they might have
// const components (they're probably pair<const X, Y>). We use
// explicit destructor invocation and placement new to get around
// this. Arg.
void set_value(value_type* dst, const value_type& src) {
dst->~value_type();
new(dst) value_type(src);
}
void destroy_buckets(size_type first, size_type last) {
for ( ; first != last; ++first)
table[first].~value_type();
}
// DELETE HELPER FUNCTIONS
// This lets the user describe a key that will indicate deleted
// table entries. This key should be an "impossible" entry --
// if you try to insert it for real, you won't be able to retrieve it!
// (NB: while you pass in an entire value, only the key part is looked
// at. This is just because I don't know how to assign just a key.)
private:
void squash_deleted() { // gets rid of any deleted entries we have
if ( num_deleted ) { // get rid of deleted before writing
dense_hashtable tmp(*this); // copying will get rid of deleted
swap(tmp); // now we are tmp
}
assert(num_deleted == 0);
}
public:
void set_deleted_key(const key_type &key) {
// the empty indicator (if specified) and the deleted indicator
// must be different
assert(!use_empty || !equals(key, get_key(emptyval)));
// It's only safe to change what "deleted" means if we purge deleted guys
squash_deleted();
use_deleted = true;
delkey = key;
}
void clear_deleted_key() {
squash_deleted();
use_deleted = false;
}
// These are public so the iterators can use them
// True if the item at position bucknum is "deleted" marker
bool test_deleted(size_type bucknum) const {
// The num_deleted test is crucial for read(): after read(), the ht values
// are garbage, and we don't want to think some of them are deleted.
return (use_deleted && num_deleted > 0 &&
equals(delkey, get_key(table[bucknum])));
}
bool test_deleted(const iterator &it) const {
return (use_deleted && num_deleted > 0 &&
equals(delkey, get_key(*it)));
}
bool test_deleted(const const_iterator &it) const {
return (use_deleted && num_deleted > 0 &&
equals(delkey, get_key(*it)));
}
// Set it so test_deleted is true. true if object didn't used to be deleted
// See below (at erase()) to explain why we allow const_iterators
bool set_deleted(const_iterator &it) {
assert(use_deleted); // bad if set_deleted_key() wasn't called
bool retval = !test_deleted(it);
// &* converts from iterator to value-type
set_key(const_cast<value_type*>(&(*it)), delkey);
return retval;
}
// Set it so test_deleted is false. true if object used to be deleted
bool clear_deleted(const_iterator &it) {
assert(use_deleted); // bad if set_deleted_key() wasn't called
// happens automatically when we assign something else in its place
return test_deleted(it);
}
// EMPTY HELPER FUNCTIONS
// This lets the user describe a key that will indicate empty (unused)
// table entries. This key should be an "impossible" entry --
// if you try to insert it for real, you won't be able to retrieve it!
// (NB: while you pass in an entire value, only the key part is looked
// at. This is just because I don't know how to assign just a key.)
public:
// These are public so the iterators can use them
// True if the item at position bucknum is "empty" marker
bool test_empty(size_type bucknum) const {
assert(use_empty); // we always need to know what's empty!
return equals(get_key(emptyval), get_key(table[bucknum]));
}
bool test_empty(const iterator &it) const {
assert(use_empty); // we always need to know what's empty!
return equals(get_key(emptyval), get_key(*it));
}
bool test_empty(const const_iterator &it) const {
assert(use_empty); // we always need to know what's empty!
return equals(get_key(emptyval), get_key(*it));
}
private:
// You can either set a range empty or an individual element
void set_empty(size_type bucknum) {
assert(use_empty);
set_value(&table[bucknum], emptyval);
}
void fill_range_with_empty(value_type* table_start, value_type* table_end) {
// Like set_empty(range), but doesn't destroy previous contents
STL_NAMESPACE::uninitialized_fill(table_start, table_end, emptyval);
}
void set_empty(size_type buckstart, size_type buckend) {
assert(use_empty);
destroy_buckets(buckstart, buckend);
fill_range_with_empty(table + buckstart, table + buckend);
}
public:
// TODO(csilvers): change all callers of this to pass in a key instead,
// and take a const key_type instead of const value_type.
void set_empty_key(const value_type &val) {
// Once you set the empty key, you can't change it
assert(!use_empty);
// The deleted indicator (if specified) and the empty indicator
// must be different.
assert(!use_deleted || !equals(get_key(val), delkey));
use_empty = true;
set_value(&emptyval, val);
assert(!table); // must set before first use
// num_buckets was set in constructor even though table was NULL
table = (value_type *) malloc(num_buckets * sizeof(*table));
assert(table);
fill_range_with_empty(table, table + num_buckets);
}
// FUNCTIONS CONCERNING SIZE
public:
size_type size() const { return num_elements - num_deleted; }
// Buckets are always a power of 2
size_type max_size() const { return (size_type(-1) >> 1U) + 1; }
bool empty() const { return size() == 0; }
size_type bucket_count() const { return num_buckets; }
size_type max_bucket_count() const { return max_size(); }
size_type nonempty_bucket_count() const { return num_elements; }
// These are tr1 methods. Their idea of 'bucket' doesn't map well to
// what we do. We just say every bucket has 0 or 1 items in it.
size_type bucket_size(size_type i) const {
return begin(i) == end(i) ? 0 : 1;
}
private:
// Because of the above, size_type(-1) is never legal; use it for errors
static const size_type ILLEGAL_BUCKET = size_type(-1);
private:
// This is the smallest size a hashtable can be without being too crowded
// If you like, you can give a min #buckets as well as a min #elts
size_type min_size(size_type num_elts, size_type min_buckets_wanted) {
size_type sz = HT_MIN_BUCKETS; // min buckets allowed
while ( sz < min_buckets_wanted || num_elts >= sz * enlarge_resize_percent )
sz *= 2;
return sz;
}
// Used after a string of deletes
void maybe_shrink() {
assert(num_elements >= num_deleted);
assert((bucket_count() & (bucket_count()-1)) == 0); // is a power of two
assert(bucket_count() >= HT_MIN_BUCKETS);
// If you construct a hashtable with < HT_DEFAULT_STARTING_BUCKETS,
// we'll never shrink until you get relatively big, and we'll never
// shrink below HT_DEFAULT_STARTING_BUCKETS. Otherwise, something
// like "dense_hash_set<int> x; x.insert(4); x.erase(4);" will
// shrink us down to HT_MIN_BUCKETS buckets, which is too small.
if (shrink_threshold > 0 &&
(num_elements-num_deleted) < shrink_threshold &&
bucket_count() > HT_DEFAULT_STARTING_BUCKETS ) {
size_type sz = bucket_count() / 2; // find how much we should shrink
while ( sz > HT_DEFAULT_STARTING_BUCKETS &&
(num_elements - num_deleted) < sz * shrink_resize_percent )
sz /= 2; // stay a power of 2
dense_hashtable tmp(*this, sz); // Do the actual resizing
swap(tmp); // now we are tmp
}
consider_shrink = false; // because we just considered it
}
// We'll let you resize a hashtable -- though this makes us copy all!
// When you resize, you say, "make it big enough for this many more elements"
void resize_delta(size_type delta) {
if ( consider_shrink ) // see if lots of deletes happened
maybe_shrink();
if ( bucket_count() > HT_MIN_BUCKETS &&
(num_elements + delta) <= enlarge_threshold )
return; // we're ok as we are
// Sometimes, we need to resize just to get rid of all the
// "deleted" buckets that are clogging up the hashtable. So when
// deciding whether to resize, count the deleted buckets (which
// are currently taking up room). But later, when we decide what
// size to resize to, *don't* count deleted buckets, since they
// get discarded during the resize.
const size_type needed_size = min_size(num_elements + delta, 0);
if ( needed_size > bucket_count() ) { // we don't have enough buckets
const size_type resize_to = min_size(num_elements - num_deleted + delta,
0);
dense_hashtable tmp(*this, resize_to);
swap(tmp); // now we are tmp
}
}
// Increase number of buckets, assuming value_type has trivial copy
// constructor and destructor. (Really, we want it to have "trivial
// move", because that's what realloc does. But there's no way to
// capture that using type_traits, so we pretend that move(x, y) is
// equivalent to "x.~T(); new(x) T(y);" which is pretty much
// correct, if a bit conservative.)
void expand_array(size_t resize_to, true_type) {
table = (value_type *) realloc(table, resize_to * sizeof(value_type));
assert(table);
fill_range_with_empty(table + num_buckets, table + resize_to);
}
// Increase number of buckets, without special assumptions about value_type.
// TODO(austern): make this exception safe. Handle exceptions from
// value_type's copy constructor.
void expand_array(size_t resize_to, false_type) {
value_type* new_table =
(value_type *) malloc(resize_to * sizeof(value_type));
assert(new_table);
STL_NAMESPACE::uninitialized_copy(table, table + num_buckets, new_table);
fill_range_with_empty(new_table + num_buckets, new_table + resize_to);
destroy_buckets(0, num_buckets);
free(table);
table = new_table;
}
// Used to actually do the rehashing when we grow/shrink a hashtable
void copy_from(const dense_hashtable &ht, size_type min_buckets_wanted) {
clear(); // clear table, set num_deleted to 0
// If we need to change the size of our table, do it now
const size_type resize_to = min_size(ht.size(), min_buckets_wanted);
if ( resize_to > bucket_count() ) { // we don't have enough buckets
typedef integral_constant<bool,
(has_trivial_copy<value_type>::value &&
has_trivial_destructor<value_type>::value)>
realloc_ok; // we pretend mv(x,y) == "x.~T(); new(x) T(y)"
expand_array(resize_to, realloc_ok());
num_buckets = resize_to;
reset_thresholds();
}
// We use a normal iterator to get non-deleted bcks from ht
// We could use insert() here, but since we know there are
// no duplicates and no deleted items, we can be more efficient
assert((bucket_count() & (bucket_count()-1)) == 0); // a power of two
for ( const_iterator it = ht.begin(); it != ht.end(); ++it ) {
size_type num_probes = 0; // how many times we've probed
size_type bucknum;
const size_type bucket_count_minus_one = bucket_count() - 1;
for (bucknum = hash(get_key(*it)) & bucket_count_minus_one;
!test_empty(bucknum); // not empty
bucknum = (bucknum + JUMP_(key, num_probes)) & bucket_count_minus_one) {
++num_probes;
assert(num_probes < bucket_count()); // or else the hashtable is full
}
set_value(&table[bucknum], *it); // copies the value to here
num_elements++;
}
}
// Required by the spec for hashed associative container
public:
// Though the docs say this should be num_buckets, I think it's much
// more useful as req_elements. As a special feature, calling with
// req_elements==0 will cause us to shrink if we can, saving space.
void resize(size_type req_elements) { // resize to this or larger
if ( consider_shrink || req_elements == 0 )
maybe_shrink();
if ( req_elements > num_elements )
return resize_delta(req_elements - num_elements);
}
// Get and change the value of shrink_resize_percent and
// enlarge_resize_percent. The description at the beginning of this
// file explains how to choose the values. Setting the shrink
// parameter to 0.0 ensures that the table never shrinks.
void get_resizing_parameters(float* shrink, float* grow) const {
*shrink = shrink_resize_percent;
*grow = enlarge_resize_percent;
}
void set_resizing_parameters(float shrink, float grow) {
assert(shrink >= 0.0);
assert(grow <= 1.0);
if (shrink > grow/2.0f)
shrink = grow / 2.0f; // otherwise we thrash hashtable size
shrink_resize_percent = shrink;
enlarge_resize_percent = grow;
reset_thresholds();
}
// CONSTRUCTORS -- as required by the specs, we take a size,
// but also let you specify a hashfunction, key comparator,
// and key extractor. We also define a copy constructor and =.
// DESTRUCTOR -- needs to free the table
explicit dense_hashtable(size_type expected_max_items_in_table = 0,
const HashFcn& hf = HashFcn(),
const EqualKey& eql = EqualKey(),
const ExtractKey& ext = ExtractKey(),
const SetKey& set = SetKey())
: hash(hf), equals(eql), get_key(ext), set_key(set), num_deleted(0),
use_deleted(false), use_empty(false),
delkey(), emptyval(), enlarge_resize_percent(HT_OCCUPANCY_FLT),
shrink_resize_percent(HT_EMPTY_FLT), table(NULL),
num_buckets(expected_max_items_in_table == 0
? HT_DEFAULT_STARTING_BUCKETS
: min_size(expected_max_items_in_table, 0)),
num_elements(0) {
// table is NULL until emptyval is set. However, we set num_buckets
// here so we know how much space to allocate once emptyval is set
reset_thresholds();
}
// As a convenience for resize(), we allow an optional second argument
// which lets you make this new hashtable a different size than ht
dense_hashtable(const dense_hashtable& ht,
size_type min_buckets_wanted = HT_DEFAULT_STARTING_BUCKETS)
: hash(ht.hash), equals(ht.equals),
get_key(ht.get_key), set_key(ht.set_key), num_deleted(0),
use_deleted(ht.use_deleted), use_empty(ht.use_empty),
delkey(ht.delkey), emptyval(ht.emptyval),
enlarge_resize_percent(ht.enlarge_resize_percent),
shrink_resize_percent(ht.shrink_resize_percent), table(NULL),
num_buckets(0), num_elements(0) {
reset_thresholds();
copy_from(ht, min_buckets_wanted); // copy_from() ignores deleted entries
}
dense_hashtable& operator= (const dense_hashtable& ht) {
if (&ht == this) return *this; // don't copy onto ourselves
clear();
hash = ht.hash;
equals = ht.equals;
get_key = ht.get_key;
set_key = ht.set_key;
use_deleted = ht.use_deleted;
use_empty = ht.use_empty;
delkey = ht.delkey;
set_value(&emptyval, ht.emptyval);
enlarge_resize_percent = ht.enlarge_resize_percent;
shrink_resize_percent = ht.shrink_resize_percent;
copy_from(ht, HT_MIN_BUCKETS); // sets num_deleted to 0 too
return *this;
}
~dense_hashtable() {
if (table) {
destroy_buckets(0, num_buckets);
free(table);
}
}
// Many STL algorithms use swap instead of copy constructors
void swap(dense_hashtable& ht) {
STL_NAMESPACE::swap(hash, ht.hash);
STL_NAMESPACE::swap(equals, ht.equals);
STL_NAMESPACE::swap(get_key, ht.get_key);
STL_NAMESPACE::swap(set_key, ht.set_key);
STL_NAMESPACE::swap(num_deleted, ht.num_deleted);
STL_NAMESPACE::swap(use_deleted, ht.use_deleted);
STL_NAMESPACE::swap(use_empty, ht.use_empty);
STL_NAMESPACE::swap(enlarge_resize_percent, ht.enlarge_resize_percent);
STL_NAMESPACE::swap(shrink_resize_percent, ht.shrink_resize_percent);
STL_NAMESPACE::swap(delkey, ht.delkey);
{ value_type tmp; // for annoying reasons, swap() doesn't work
set_value(&tmp, emptyval);
set_value(&emptyval, ht.emptyval);
set_value(&ht.emptyval, tmp);
}
STL_NAMESPACE::swap(table, ht.table);
STL_NAMESPACE::swap(num_buckets, ht.num_buckets);
STL_NAMESPACE::swap(num_elements, ht.num_elements);
reset_thresholds();
ht.reset_thresholds();
}
// It's always nice to be able to clear a table without deallocating it
void clear() {
if (table)
destroy_buckets(0, num_buckets);
num_buckets = min_size(0,0); // our new size
reset_thresholds();
table = (value_type *) realloc(table, num_buckets * sizeof(*table));
assert(table);
fill_range_with_empty(table, table + num_buckets);
num_elements = 0;
num_deleted = 0;
}
// Clear the table without resizing it.
// Mimicks the stl_hashtable's behaviour when clear()-ing in that it
// does not modify the bucket count
void clear_no_resize() {
if (table) {
set_empty(0, num_buckets);
}
// don't consider to shrink before another erase()
reset_thresholds();
num_elements = 0;
num_deleted = 0;
}
// LOOKUP ROUTINES
private:
// Returns a pair of positions: 1st where the object is, 2nd where
// it would go if you wanted to insert it. 1st is ILLEGAL_BUCKET
// if object is not found; 2nd is ILLEGAL_BUCKET if it is.
// Note: because of deletions where-to-insert is not trivial: it's the
// first deleted bucket we see, as long as we don't find the key later
pair<size_type, size_type> find_position(const key_type &key) const {
size_type num_probes = 0; // how many times we've probed
const size_type bucket_count_minus_one = bucket_count() - 1;
size_type bucknum = hash(key) & bucket_count_minus_one;
size_type insert_pos = ILLEGAL_BUCKET; // where we would insert
while ( 1 ) { // probe until something happens
if ( test_empty(bucknum) ) { // bucket is empty
if ( insert_pos == ILLEGAL_BUCKET ) // found no prior place to insert
return pair<size_type,size_type>(ILLEGAL_BUCKET, bucknum);
else
return pair<size_type,size_type>(ILLEGAL_BUCKET, insert_pos);
} else if ( test_deleted(bucknum) ) {// keep searching, but mark to insert
if ( insert_pos == ILLEGAL_BUCKET )
insert_pos = bucknum;
} else if ( equals(key, get_key(table[bucknum])) ) {
return pair<size_type,size_type>(bucknum, ILLEGAL_BUCKET);
}
++num_probes; // we're doing another probe
bucknum = (bucknum + JUMP_(key, num_probes)) & bucket_count_minus_one;
assert(num_probes < bucket_count()); // don't probe too many times!
}
}
public:
iterator find(const key_type& key) {
if ( size() == 0 ) return end();
pair<size_type, size_type> pos = find_position(key);
if ( pos.first == ILLEGAL_BUCKET ) // alas, not there
return end();
else
return iterator(this, table + pos.first, table + num_buckets, false);
}
const_iterator find(const key_type& key) const {
if ( size() == 0 ) return end();
pair<size_type, size_type> pos = find_position(key);
if ( pos.first == ILLEGAL_BUCKET ) // alas, not there
return end();
else
return const_iterator(this, table + pos.first, table+num_buckets, false);
}
// This is a tr1 method: the bucket a given key is in, or what bucket
// it would be put in, if it were to be inserted. Shrug.
size_type bucket(const key_type& key) const {
pair<size_type, size_type> pos = find_position(key);
return pos.first == ILLEGAL_BUCKET ? pos.second : pos.first;
}
// Counts how many elements have key key. For maps, it's either 0 or 1.
size_type count(const key_type &key) const {
pair<size_type, size_type> pos = find_position(key);
return pos.first == ILLEGAL_BUCKET ? 0 : 1;
}
// Likewise, equal_range doesn't really make sense for us. Oh well.
pair<iterator,iterator> equal_range(const key_type& key) {
iterator pos = find(key); // either an iterator or end
if (pos == end()) {
return pair<iterator,iterator>(pos, pos);
} else {
const iterator startpos = pos++;
return pair<iterator,iterator>(startpos, pos);
}
}
pair<const_iterator,const_iterator> equal_range(const key_type& key) const {
const_iterator pos = find(key); // either an iterator or end
if (pos == end()) {
return pair<const_iterator,const_iterator>(pos, pos);
} else {
const const_iterator startpos = pos++;
return pair<const_iterator,const_iterator>(startpos, pos);
}
}
// INSERTION ROUTINES
private:
// If you know *this is big enough to hold obj, use this routine
pair<iterator, bool> insert_noresize(const value_type& obj) {
// First, double-check we're not inserting delkey or emptyval
assert(!use_empty || !equals(get_key(obj), get_key(emptyval)));
assert(!use_deleted || !equals(get_key(obj), delkey));
const pair<size_type,size_type> pos = find_position(get_key(obj));
if ( pos.first != ILLEGAL_BUCKET) { // object was already there
return pair<iterator,bool>(iterator(this, table + pos.first,
table + num_buckets, false),
false); // false: we didn't insert
} else { // pos.second says where to put it
if ( test_deleted(pos.second) ) { // just replace if it's been del.
const_iterator delpos(this, table + pos.second, // shrug:
table + num_buckets, false);// shouldn't need const
clear_deleted(delpos);
assert( num_deleted > 0);
--num_deleted; // used to be, now it isn't
} else {
++num_elements; // replacing an empty bucket
}
set_value(&table[pos.second], obj);
return pair<iterator,bool>(iterator(this, table + pos.second,
table + num_buckets, false),
true); // true: we did insert
}
}
public:
// This is the normal insert routine, used by the outside world
pair<iterator, bool> insert(const value_type& obj) {
resize_delta(1); // adding an object, grow if need be
return insert_noresize(obj);
}
// When inserting a lot at a time, we specialize on the type of iterator
template <class InputIterator>
void insert(InputIterator f, InputIterator l) {
// specializes on iterator type
insert(f, l, typename STL_NAMESPACE::iterator_traits<InputIterator>::iterator_category());
}
// Iterator supports operator-, resize before inserting
template <class ForwardIterator>
void insert(ForwardIterator f, ForwardIterator l,
STL_NAMESPACE::forward_iterator_tag) {
size_type n = STL_NAMESPACE::distance(f, l); // TODO(csilvers): standard?
resize_delta(n);
for ( ; n > 0; --n, ++f)
insert_noresize(*f);
}
// Arbitrary iterator, can't tell how much to resize
template <class InputIterator>
void insert(InputIterator f, InputIterator l,
STL_NAMESPACE::input_iterator_tag) {
for ( ; f != l; ++f)
insert(*f);
}
// DELETION ROUTINES
size_type erase(const key_type& key) {
// First, double-check we're not trying to erase delkey or emptyval
assert(!use_empty || !equals(key, get_key(emptyval)));
assert(!use_deleted || !equals(key, delkey));
const_iterator pos = find(key); // shrug: shouldn't need to be const
if ( pos != end() ) {
assert(!test_deleted(pos)); // or find() shouldn't have returned it
set_deleted(pos);
++num_deleted;
consider_shrink = true; // will think about shrink after next insert
return 1; // because we deleted one thing
} else {
return 0; // because we deleted nothing
}
}
// This is really evil: really it should be iterator, not const_iterator.
// But...the only reason keys are const is to allow lookup.
// Since that's a moot issue for deleted keys, we allow const_iterators
void erase(const_iterator pos) {
if ( pos == end() ) return; // sanity check
if ( set_deleted(pos) ) { // true if object has been newly deleted
++num_deleted;
consider_shrink = true; // will think about shrink after next insert
}
}
void erase(const_iterator f, const_iterator l) {
for ( ; f != l; ++f) {
if ( set_deleted(f) ) // should always be true
++num_deleted;
}
consider_shrink = true; // will think about shrink after next insert
}
// COMPARISON
bool operator==(const dense_hashtable& ht) const {
if (size() != ht.size()) {
return false;
} else if (this == &ht) {
return true;
} else {
// Iterate through the elements in "this" and see if the
// corresponding element is in ht
for ( const_iterator it = begin(); it != end(); ++it ) {
const_iterator it2 = ht.find(get_key(*it));
if ((it2 == ht.end()) || (*it != *it2)) {
return false;
}
}
return true;
}
}
bool operator!=(const dense_hashtable& ht) const {
return !(*this == ht);
}
// I/O
// We support reading and writing hashtables to disk. Alas, since
// I don't know how to write a hasher or key_equal, you have to make
// sure everything but the table is the same. We compact before writing
//
// NOTE: These functions are currently TODO. They've not been implemented.
bool write_metadata(FILE *fp) {
squash_deleted(); // so we don't have to worry about delkey
return false; // TODO
}
bool read_metadata(FILE *fp) {
num_deleted = 0; // since we got rid before writing
assert(use_empty); // have to set this before calling us
if (table) free(table); // we'll make our own
// TODO: read magic number
// TODO: read num_buckets
reset_thresholds();
table = (value_type *) malloc(num_buckets * sizeof(*table));
assert(table);
fill_range_with_empty(table, table + num_buckets);
// TODO: read num_elements
for ( size_type i = 0; i < num_elements; ++i ) {
// TODO: read bucket_num
// TODO: set with non-empty, non-deleted value
}
return false; // TODO
}
// If your keys and values are simple enough, we can write them to
// disk for you. "simple enough" means value_type is a POD type
// that contains no pointers. However, we don't try to normalize
// endianness
bool write_nopointer_data(FILE *fp) const {
for ( const_iterator it = begin(); it != end(); ++it ) {
// TODO: skip empty/deleted values
if ( !fwrite(&*it, sizeof(*it), 1, fp) ) return false;
}
return false;
}
// When reading, we have to override the potential const-ness of *it
bool read_nopointer_data(FILE *fp) {
for ( iterator it = begin(); it != end(); ++it ) {
// TODO: skip empty/deleted values
if ( !fread(reinterpret_cast<void*>(&(*it)), sizeof(*it), 1, fp) )
return false;
}
return false;
}
private:
// The actual data
hasher hash; // required by hashed_associative_container
key_equal equals;
ExtractKey get_key;
SetKey set_key;
size_type num_deleted; // how many occupied buckets are marked deleted
bool use_deleted; // false until delkey has been set
bool use_empty; // you must do this before you start
// TODO(csilvers): make a pointer, and get rid of use_deleted (benchmark!)
key_type delkey; // which key marks deleted entries
value_type emptyval; // which key marks unused entries
float enlarge_resize_percent; // how full before resize
float shrink_resize_percent; // how empty before resize
size_type shrink_threshold; // num_buckets * shrink_resize_percent
size_type enlarge_threshold; // num_buckets * enlarge_resize_percent
value_type *table;
size_type num_buckets;
size_type num_elements;
bool consider_shrink; // true if we should try to shrink before next insert
void reset_thresholds() {
enlarge_threshold = static_cast<size_type>(num_buckets
* enlarge_resize_percent);
shrink_threshold = static_cast<size_type>(num_buckets
* shrink_resize_percent);
consider_shrink = false; // whatever caused us to reset already considered
}
};
// We need a global swap as well
template <class V, class K, class HF, class ExK, class SetK, class EqK, class A>
inline void swap(dense_hashtable<V,K,HF,ExK,SetK,EqK,A> &x,
dense_hashtable<V,K,HF,ExK,SetK,EqK,A> &y) {
x.swap(y);
}
#undef JUMP_
template <class V, class K, class HF, class ExK, class SetK, class EqK, class A>
const typename dense_hashtable<V,K,HF,ExK,SetK,EqK,A>::size_type
dense_hashtable<V,K,HF,ExK,SetK,EqK,A>::ILLEGAL_BUCKET;
// How full we let the table get before we resize. Knuth says .8 is
// good -- higher causes us to probe too much, though saves memory.
// However, we go with .5, getting better performance at the cost of
// more space (a trade-off densehashtable explicitly chooses to make).
// Feel free to play around with different values, though.
template <class V, class K, class HF, class ExK, class SetK, class EqK, class A>
const float dense_hashtable<V,K,HF,ExK,SetK,EqK,A>::HT_OCCUPANCY_FLT = 0.5f;
// How empty we let the table get before we resize lower.
// It should be less than OCCUPANCY_FLT / 2 or we thrash resizing
template <class V, class K, class HF, class ExK, class SetK, class EqK, class A>
const float dense_hashtable<V,K,HF,ExK,SetK,EqK,A>::HT_EMPTY_FLT
= 0.4f * dense_hashtable<V,K,HF,ExK,SetK,EqK,A>::HT_OCCUPANCY_FLT;
_END_GOOGLE_NAMESPACE_
#endif /* _DENSEHASHTABLE_H_ */