SequenceToOffsetTable.h revision 263508 
1//===-- SequenceToOffsetTable.h - Compress similar sequences ----*- 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// SequenceToOffsetTable can be used to emit a number of null-terminated
11// sequences as one big array.  Use the same memory when a sequence is a suffix
12// of another.
13//
14//===----------------------------------------------------------------------===//
15
16#ifndef TBLGEN_SEQUENCE_TO_OFFSET_TABLE_H
17#define TBLGEN_SEQUENCE_TO_OFFSET_TABLE_H
18
19#include "llvm/Support/raw_ostream.h"
20#include <algorithm>
21#include <cassert>
22#include <cctype>
23#include <functional>
24#include <map>
25#include <vector>
26
27namespace llvm {
28
29/// SequenceToOffsetTable - Collect a number of terminated sequences of T.
30/// Compute the layout of a table that contains all the sequences, possibly by
31/// reusing entries.
32///
33/// @tparam SeqT The sequence container. (vector or string).
34/// @tparam Less A stable comparator for SeqT elements.
35template<typename SeqT, typename Less = std::less<typename SeqT::value_type> >
36class SequenceToOffsetTable {
37  typedef typename SeqT::value_type ElemT;
38
39  // Define a comparator for SeqT that sorts a suffix immediately before a
40  // sequence with that suffix.
41  struct SeqLess : public std::binary_function<SeqT, SeqT, bool> {
42    Less L;
43    bool operator()(const SeqT &A, const SeqT &B) const {
44      return std::lexicographical_compare(A.rbegin(), A.rend(),
45                                          B.rbegin(), B.rend(), L);
46    }
47  };
48
49  // Keep sequences ordered according to SeqLess so suffixes are easy to find.
50  // Map each sequence to its offset in the table.
51  typedef std::map<SeqT, unsigned, SeqLess> SeqMap;
52
53  // Sequences added so far, with suffixes removed.
54  SeqMap Seqs;
55
56  // Entries in the final table, or 0 before layout was called.
57  unsigned Entries;
58
59  // isSuffix - Returns true if A is a suffix of B.
60  static bool isSuffix(const SeqT &A, const SeqT &B) {
61    return A.size() <= B.size() && std::equal(A.rbegin(), A.rend(), B.rbegin());
62  }
63
64public:
65  SequenceToOffsetTable() : Entries(0) {}
66
67  /// add - Add a sequence to the table.
68  /// This must be called before layout().
69  void add(const SeqT &Seq) {
70    assert(Entries == 0 && "Cannot call add() after layout()");
71    typename SeqMap::iterator I = Seqs.lower_bound(Seq);
72
73    // If SeqMap contains a sequence that has Seq as a suffix, I will be
74    // pointing to it.
75    if (I != Seqs.end() && isSuffix(Seq, I->first))
76      return;
77
78    I = Seqs.insert(I, std::make_pair(Seq, 0u));
79
80    // The entry before I may be a suffix of Seq that can now be erased.
81    if (I != Seqs.begin() && isSuffix((--I)->first, Seq))
82      Seqs.erase(I);
83  }
84
85  bool empty() const { return Seqs.empty(); }
86
87  /// layout - Computes the final table layout.
88  void layout() {
89    assert(Entries == 0 && "Can only call layout() once");
90    // Lay out the table in Seqs iteration order.
91    for (typename SeqMap::iterator I = Seqs.begin(), E = Seqs.end(); I != E;
92         ++I) {
93      I->second = Entries;
94      // Include space for a terminator.
95      Entries += I->first.size() + 1;
96    }
97  }
98
99  /// get - Returns the offset of Seq in the final table.
100  unsigned get(const SeqT &Seq) const {
101    assert(Entries && "Call layout() before get()");
102    typename SeqMap::const_iterator I = Seqs.lower_bound(Seq);
103    assert(I != Seqs.end() && isSuffix(Seq, I->first) &&
104           "get() called with sequence that wasn't added first");
105    return I->second + (I->first.size() - Seq.size());
106  }
107
108  /// emit - Print out the table as the body of an array initializer.
109  /// Use the Print function to print elements.
110  void emit(raw_ostream &OS,
111            void (*Print)(raw_ostream&, ElemT),
112            const char *Term = "0") const {
113    assert(Entries && "Call layout() before emit()");
114    for (typename SeqMap::const_iterator I = Seqs.begin(), E = Seqs.end();
115         I != E; ++I) {
116      OS << "  /* " << I->second << " */ ";
117      for (typename SeqT::const_iterator SI = I->first.begin(),
118             SE = I->first.end(); SI != SE; ++SI) {
119        Print(OS, *SI);
120        OS << ", ";
121      }
122      OS << Term << ",\n";
123    }
124  }
125};
126
127// Helper function for SequenceToOffsetTable<string>.
128static inline void printChar(raw_ostream &OS, char C) {
129  unsigned char UC(C);
130  if (isalnum(UC) || ispunct(UC)) {
131    OS << '\'';
132    if (C == '\\' || C == '\'')
133      OS << '\\';
134    OS << C << '\'';
135  } else {
136    OS << unsigned(UC);
137  }
138}
139
140} // end namespace llvm
141
142#endif
143