1//===- llvm/ADT/SmallSet.h - 'Normally small' sets --------------*- C++ -*-===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file defines the SmallSet class.
11//
12//===----------------------------------------------------------------------===//
13
14#ifndef LLVM_ADT_SMALLSET_H
15#define LLVM_ADT_SMALLSET_H
16
17#include "llvm/ADT/None.h"
18#include "llvm/ADT/SmallPtrSet.h"
19#include "llvm/ADT/SmallVector.h"
20#include <set>
21
22namespace llvm {
23
24/// SmallSet - This maintains a set of unique values, optimizing for the case
25/// when the set is small (less than N).  In this case, the set can be
26/// maintained with no mallocs.  If the set gets large, we expand to using an
27/// std::set to maintain reasonable lookup times.
28///
29/// Note that this set does not provide a way to iterate over members in the
30/// set.
31template <typename T, unsigned N,  typename C = std::less<T> >
32class SmallSet {
33  /// Use a SmallVector to hold the elements here (even though it will never
34  /// reach its 'large' stage) to avoid calling the default ctors of elements
35  /// we will never use.
36  SmallVector<T, N> Vector;
37  std::set<T, C> Set;
38  typedef typename SmallVector<T, N>::const_iterator VIterator;
39  typedef typename SmallVector<T, N>::iterator mutable_iterator;
40public:
41  typedef size_t size_type;
42  SmallSet() {}
43
44  bool LLVM_ATTRIBUTE_UNUSED_RESULT empty() const {
45    return Vector.empty() && Set.empty();
46  }
47
48  size_type size() const {
49    return isSmall() ? Vector.size() : Set.size();
50  }
51
52  /// count - Return 1 if the element is in the set, 0 otherwise.
53  size_type count(const T &V) const {
54    if (isSmall()) {
55      // Since the collection is small, just do a linear search.
56      return vfind(V) == Vector.end() ? 0 : 1;
57    } else {
58      return Set.count(V);
59    }
60  }
61
62  /// insert - Insert an element into the set if it isn't already there.
63  /// Returns true if the element is inserted (it was not in the set before).
64  /// The first value of the returned pair is unused and provided for
65  /// partial compatibility with the standard library self-associative container
66  /// concept.
67  // FIXME: Add iterators that abstract over the small and large form, and then
68  // return those here.
69  std::pair<NoneType, bool> insert(const T &V) {
70    if (!isSmall())
71      return std::make_pair(None, Set.insert(V).second);
72
73    VIterator I = vfind(V);
74    if (I != Vector.end())    // Don't reinsert if it already exists.
75      return std::make_pair(None, false);
76    if (Vector.size() < N) {
77      Vector.push_back(V);
78      return std::make_pair(None, true);
79    }
80
81    // Otherwise, grow from vector to set.
82    while (!Vector.empty()) {
83      Set.insert(Vector.back());
84      Vector.pop_back();
85    }
86    Set.insert(V);
87    return std::make_pair(None, true);
88  }
89
90  template <typename IterT>
91  void insert(IterT I, IterT E) {
92    for (; I != E; ++I)
93      insert(*I);
94  }
95
96  bool erase(const T &V) {
97    if (!isSmall())
98      return Set.erase(V);
99    for (mutable_iterator I = Vector.begin(), E = Vector.end(); I != E; ++I)
100      if (*I == V) {
101        Vector.erase(I);
102        return true;
103      }
104    return false;
105  }
106
107  void clear() {
108    Vector.clear();
109    Set.clear();
110  }
111private:
112  bool isSmall() const { return Set.empty(); }
113
114  VIterator vfind(const T &V) const {
115    for (VIterator I = Vector.begin(), E = Vector.end(); I != E; ++I)
116      if (*I == V)
117        return I;
118    return Vector.end();
119  }
120};
121
122/// If this set is of pointer values, transparently switch over to using
123/// SmallPtrSet for performance.
124template <typename PointeeType, unsigned N>
125class SmallSet<PointeeType*, N> : public SmallPtrSet<PointeeType*, N> {};
126
127} // end namespace llvm
128
129#endif
130