// Copyright 2006 The RE2 Authors. All Rights Reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// DESCRIPTION
//
// SparseSet<T>(m) is a set of integers in [0, m).
// It requires sizeof(int)*m memory, but it provides
// fast iteration through the elements in the set and fast clearing
// of the set.
//
// Insertion and deletion are constant time operations.
//
// Allocating the set is a constant time operation
// when memory allocation is a constant time operation.
//
// Clearing the set is a constant time operation (unusual!).
//
// Iterating through the set is an O(n) operation, where n
// is the number of items in the set (not O(m)).
//
// The set iterator visits entries in the order they were first
// inserted into the array. It is safe to add items to the set while
// using an iterator: the iterator will visit indices added to the set
// during the iteration, but will not re-visit indices whose values
// change after visiting. Thus SparseSet can be a convenient
// implementation of a work queue.
//
// The SparseSet implementation is NOT thread-safe. It is up to the
// caller to make sure only one thread is accessing the set. (Typically
// these sets are temporary values and used in situations where speed is
// important.)
//
// The SparseSet interface does not present all the usual STL bells and
// whistles.
//
// Implemented with reference to Briggs & Torczon, An Efficient
// Representation for Sparse Sets, ACM Letters on Programming Languages
// and Systems, Volume 2, Issue 1-4 (March-Dec. 1993), pp. 59-69.
//
// For a generalization to sparse array, see sparse_array.h.
// IMPLEMENTATION
//
// See sparse_array.h for implementation details
#ifndef RE2_UTIL_SPARSE_SET_H__
#define RE2_UTIL_SPARSE_SET_H__
#include "util/util.h"
namespace re2 {
class SparseSet {
public:
SparseSet()
: size_(0), max_size_(0), sparse_to_dense_(NULL), dense_(NULL),
valgrind_(RunningOnValgrindOrMemorySanitizer()) {}
SparseSet(int max_size) {
max_size_ = max_size;
sparse_to_dense_ = new int[max_size];
dense_ = new int[max_size];
valgrind_ = RunningOnValgrindOrMemorySanitizer();
// Don't need to zero the memory, but do so anyway
// to appease Valgrind.
if (valgrind_) {
for (int i = 0; i < max_size; i++) {
dense_[i] = 0xababababU;
sparse_to_dense_[i] = 0xababababU;
}
}
size_ = 0;
}
~SparseSet() {
delete[] sparse_to_dense_;
delete[] dense_;
}
typedef int* iterator;
typedef const int* const_iterator;
int size() const { return size_; }
iterator begin() { return dense_; }
iterator end() { return dense_ + size_; }
const_iterator begin() const { return dense_; }
const_iterator end() const { return dense_ + size_; }
// Change the maximum size of the array.
// Invalidates all iterators.
void resize(int new_max_size) {
if (size_ > new_max_size)
size_ = new_max_size;
if (new_max_size > max_size_) {
int* a = new int[new_max_size];
if (sparse_to_dense_) {
memmove(a, sparse_to_dense_, max_size_*sizeof a[0]);
if (valgrind_) {
for (int i = max_size_; i < new_max_size; i++)
a[i] = 0xababababU;
}
delete[] sparse_to_dense_;
}
sparse_to_dense_ = a;
a = new int[new_max_size];
if (dense_) {
memmove(a, dense_, size_*sizeof a[0]);
if (valgrind_) {
for (int i = size_; i < new_max_size; i++)
a[i] = 0xababababU;
}
delete[] dense_;
}
dense_ = a;
}
max_size_ = new_max_size;
}
// Return the maximum size of the array.
// Indices can be in the range [0, max_size).
int max_size() const { return max_size_; }
// Clear the array.
void clear() { size_ = 0; }
// Check whether i is in the array.
bool contains(int i) const {
DCHECK_GE(i, 0);
DCHECK_LT(i, max_size_);
if (static_cast<uint>(i) >= max_size_) {
return false;
}
// Unsigned comparison avoids checking sparse_to_dense_[i] < 0.
return (uint)sparse_to_dense_[i] < (uint)size_ &&
dense_[sparse_to_dense_[i]] == i;
}
// Adds i to the set.
void insert(int i) {
if (!contains(i))
insert_new(i);
}
// Set the value at the new index i to v.
// Fast but unsafe: only use if contains(i) is false.
void insert_new(int i) {
if (static_cast<uint>(i) >= max_size_) {
// Semantically, end() would be better here, but we already know
// the user did something stupid, so begin() insulates them from
// dereferencing an invalid pointer.
return;
}
DCHECK(!contains(i));
DCHECK_LT(size_, max_size_);
sparse_to_dense_[i] = size_;
dense_[size_] = i;
size_++;
}
// Comparison function for sorting.
// Can sort the sparse array so that future iterations
// will visit indices in increasing order using
// sort(arr.begin(), arr.end(), arr.less);
static bool less(int a, int b) { return a < b; }
private:
int size_;
int max_size_;
int* sparse_to_dense_;
int* dense_;
bool valgrind_;
DISALLOW_EVIL_CONSTRUCTORS(SparseSet);
};
} // namespace re2
#endif // RE2_UTIL_SPARSE_SET_H__