llvm-6502/include/llvm/ADT/SparseSet.h
2012-02-23 08:23:53 +00:00

269 lines
9.5 KiB
C++

//===--- llvm/ADT/SparseSet.h - Sparse set ----------------------*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines the SparseSet class derived from the version described in
// Briggs, Torczon, "An efficient representation for sparse sets", ACM Letters
// on Programming Languages and Systems, Volume 2 Issue 1-4, March-Dec. 1993.
//
// A sparse set holds a small number of objects identified by integer keys from
// a moderately sized universe. The sparse set uses more memory than other
// containers in order to provide faster operations.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_ADT_SPARSESET_H
#define LLVM_ADT_SPARSESET_H
#include "llvm/ADT/SmallVector.h"
#include "llvm/Support/DataTypes.h"
#include <limits>
namespace llvm {
/// SparseSetFunctor - Objects in a SparseSet are identified by small integer
/// keys. A functor object is used to compute the key of an object. The
/// functor's operator() must return an unsigned smaller than the universe.
///
/// The default functor implementation forwards to a getSparseSetKey() method
/// on the object. It is intended for sparse sets holding ad-hoc structs.
///
template<typename ValueT>
struct SparseSetFunctor {
unsigned operator()(const ValueT &Val) {
return Val.getSparseSetKey();
}
};
/// SparseSetFunctor<unsigned> - Provide a trivial identity functor for
/// SparseSet<unsigned>.
///
template<> struct SparseSetFunctor<unsigned> {
unsigned operator()(unsigned Val) { return Val; }
};
/// SparseSet - Fast set implementation for objects that can be identified by
/// small unsigned keys.
///
/// SparseSet allocates memory proportional to the size of the key universe, so
/// it is not recommended for building composite data structures. It is useful
/// for algorithms that require a single set with fast operations.
///
/// Compared to DenseSet and DenseMap, SparseSet provides constant-time fast
/// clear() and iteration as fast as a vector. The find(), insert(), and
/// erase() operations are all constant time, and typically faster than a hash
/// table. The iteration order doesn't depend on numerical key values, it only
/// depends on the order of insert() and erase() operations. When no elements
/// have been erased, the iteration order is the insertion order.
///
/// Compared to BitVector, SparseSet<unsigned> uses 8x-40x more memory, but
/// offers constant-time clear() and size() operations as well as fast
/// iteration independent on the size of the universe.
///
/// SparseSet contains a dense vector holding all the objects and a sparse
/// array holding indexes into the dense vector. Most of the memory is used by
/// the sparse array which is the size of the key universe. The SparseT
/// template parameter provides a space/speed tradeoff for sets holding many
/// elements.
///
/// When SparseT is uint32_t, find() only touches 2 cache lines, but the sparse
/// array uses 4 x Universe bytes.
///
/// When SparseT is uint8_t (the default), find() touches up to 2+[N/256] cache
/// lines, but the sparse array is 4x smaller. N is the number of elements in
/// the set.
///
/// For sets that may grow to thousands of elements, SparseT should be set to
/// uint16_t or uint32_t.
///
/// @param ValueT The type of objects in the set.
/// @param SparseT An unsigned integer type. See above.
/// @param KeyFunctorT A functor that computes the unsigned key of a ValueT.
///
template<typename ValueT,
typename SparseT = uint8_t,
typename KeyFunctorT = SparseSetFunctor<ValueT> >
class SparseSet {
typedef SmallVector<ValueT, 8> DenseT;
DenseT Dense;
SparseT *Sparse;
unsigned Universe;
KeyFunctorT KeyOf;
// Disable copy construction and assignment.
// This data structure is not meant to be used that way.
SparseSet(const SparseSet&); // DO NOT IMPLEMENT.
SparseSet &operator=(const SparseSet&); // DO NOT IMPLEMENT.
public:
typedef ValueT value_type;
typedef ValueT &reference;
typedef const ValueT &const_reference;
typedef ValueT *pointer;
typedef const ValueT *const_pointer;
SparseSet() : Sparse(0), Universe(0) {}
~SparseSet() { free(Sparse); }
/// setUniverse - Set the universe size which determines the largest key the
/// set can hold. The universe must be sized before any elements can be
/// added.
///
/// @param U Universe size. All object keys must be less than U.
///
void setUniverse(unsigned U) {
// It's not hard to resize the universe on a non-empty set, but it doesn't
// seem like a likely use case, so we can add that code when we need it.
assert(empty() && "Can only resize universe on an empty map");
// Hysteresis prevents needless reallocations.
if (U >= Universe/4 && U <= Universe)
return;
free(Sparse);
// The Sparse array doesn't actually need to be initialized, so malloc
// would be enough here, but that will cause tools like valgrind to
// complain about branching on uninitialized data.
Sparse = reinterpret_cast<SparseT*>(calloc(U, sizeof(SparseT)));
Universe = U;
}
// Import trivial vector stuff from DenseT.
typedef typename DenseT::iterator iterator;
typedef typename DenseT::const_iterator const_iterator;
const_iterator begin() const { return Dense.begin(); }
const_iterator end() const { return Dense.end(); }
iterator begin() { return Dense.begin(); }
iterator end() { return Dense.end(); }
/// empty - Returns true if the set is empty.
///
/// This is not the same as BitVector::empty().
///
bool empty() const { return Dense.empty(); }
/// size - Returns the number of elements in the set.
///
/// This is not the same as BitVector::size() which returns the size of the
/// universe.
///
unsigned size() const { return Dense.size(); }
/// clear - Clears the set. This is a very fast constant time operation.
///
void clear() {
// Sparse does not need to be cleared, see find().
Dense.clear();
}
/// find - Find an element by its key.
///
/// @param Key A valid key to find.
/// @returns An iterator to the element identified by key, or end().
///
iterator find(unsigned Key) {
assert(Key < Universe && "Key out of range");
assert(std::numeric_limits<SparseT>::is_integer &&
!std::numeric_limits<SparseT>::is_signed &&
"SparseT must be an unsigned integer type");
const unsigned Stride = std::numeric_limits<SparseT>::max() + 1u;
for (unsigned i = Sparse[Key], e = size(); i < e; i += Stride) {
const unsigned FoundKey = KeyOf(Dense[i]);
assert(FoundKey < Universe && "Invalid key in set. Did object mutate?");
if (Key == FoundKey)
return begin() + i;
// Stride is 0 when SparseT >= unsigned. We don't need to loop.
if (!Stride)
break;
}
return end();
}
const_iterator find(unsigned Key) const {
return const_cast<SparseSet*>(this)->find(Key);
}
/// count - Returns true if this set contains an element identified by Key.
///
bool count(unsigned Key) const {
return find(Key) != end();
}
/// insert - Attempts to insert a new element.
///
/// If Val is successfully inserted, return (I, true), where I is an iterator
/// pointing to the newly inserted element.
///
/// If the set already contains an element with the same key as Val, return
/// (I, false), where I is an iterator pointing to the existing element.
///
/// Insertion invalidates all iterators.
///
std::pair<iterator, bool> insert(const ValueT &Val) {
unsigned Key = KeyOf(Val);
iterator I = find(Key);
if (I != end())
return std::make_pair(I, false);
Sparse[Key] = size();
Dense.push_back(Val);
return std::make_pair(end() - 1, true);
}
/// array subscript - If an element already exists with this key, return it.
/// Otherwise, automatically construct a new value from Key, insert it,
/// and return the newly inserted element.
ValueT &operator[](unsigned Key) {
return *insert(ValueT(Key)).first;
}
/// erase - Erases an existing element identified by a valid iterator.
///
/// This invalidates all iterators, but erase() returns an iterator pointing
/// to the next element. This makes it possible to erase selected elements
/// while iterating over the set:
///
/// for (SparseSet::iterator I = Set.begin(); I != Set.end();)
/// if (test(*I))
/// I = Set.erase(I);
/// else
/// ++I;
///
/// Note that end() changes when elements are erased, unlike std::list.
///
iterator erase(iterator I) {
assert(unsigned(I - begin()) < size() && "Invalid iterator");
if (I != end() - 1) {
*I = Dense.back();
unsigned BackKey = KeyOf(Dense.back());
assert(BackKey < Universe && "Invalid key in set. Did object mutate?");
Sparse[BackKey] = I - begin();
}
// This depends on SmallVector::pop_back() not invalidating iterators.
// std::vector::pop_back() doesn't give that guarantee.
Dense.pop_back();
return I;
}
/// erase - Erases an element identified by Key, if it exists.
///
/// @param Key The key identifying the element to erase.
/// @returns True when an element was erased, false if no element was found.
///
bool erase(unsigned Key) {
iterator I = find(Key);
if (I == end())
return false;
erase(I);
return true;
}
};
} // end namespace llvm
#endif