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      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 LLVM_UTILS_TABLEGEN_SEQUENCETOOFFSETTABLE_H
     17 #define LLVM_UTILS_TABLEGEN_SEQUENCETOOFFSETTABLE_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 
     26 namespace llvm {
     27 
     28 /// SequenceToOffsetTable - Collect a number of terminated sequences of T.
     29 /// Compute the layout of a table that contains all the sequences, possibly by
     30 /// reusing entries.
     31 ///
     32 /// @tparam SeqT The sequence container. (vector or string).
     33 /// @tparam Less A stable comparator for SeqT elements.
     34 template<typename SeqT, typename Less = std::less<typename SeqT::value_type> >
     35 class SequenceToOffsetTable {
     36   typedef typename SeqT::value_type ElemT;
     37 
     38   // Define a comparator for SeqT that sorts a suffix immediately before a
     39   // sequence with that suffix.
     40   struct SeqLess {
     41     Less L;
     42     bool operator()(const SeqT &A, const SeqT &B) const {
     43       return std::lexicographical_compare(A.rbegin(), A.rend(),
     44                                           B.rbegin(), B.rend(), L);
     45     }
     46   };
     47 
     48   // Keep sequences ordered according to SeqLess so suffixes are easy to find.
     49   // Map each sequence to its offset in the table.
     50   typedef std::map<SeqT, unsigned, SeqLess> SeqMap;
     51 
     52   // Sequences added so far, with suffixes removed.
     53   SeqMap Seqs;
     54 
     55   // Entries in the final table, or 0 before layout was called.
     56   unsigned Entries;
     57 
     58   // isSuffix - Returns true if A is a suffix of B.
     59   static bool isSuffix(const SeqT &A, const SeqT &B) {
     60     return A.size() <= B.size() && std::equal(A.rbegin(), A.rend(), B.rbegin());
     61   }
     62 
     63 public:
     64   SequenceToOffsetTable() : Entries(0) {}
     65 
     66   /// add - Add a sequence to the table.
     67   /// This must be called before layout().
     68   void add(const SeqT &Seq) {
     69     assert(Entries == 0 && "Cannot call add() after layout()");
     70     typename SeqMap::iterator I = Seqs.lower_bound(Seq);
     71 
     72     // If SeqMap contains a sequence that has Seq as a suffix, I will be
     73     // pointing to it.
     74     if (I != Seqs.end() && isSuffix(Seq, I->first))
     75       return;
     76 
     77     I = Seqs.insert(I, std::make_pair(Seq, 0u));
     78 
     79     // The entry before I may be a suffix of Seq that can now be erased.
     80     if (I != Seqs.begin() && isSuffix((--I)->first, Seq))
     81       Seqs.erase(I);
     82   }
     83 
     84   bool empty() const { return Seqs.empty(); }
     85 
     86   unsigned size() const {
     87     assert(Entries && "Call layout() before size()");
     88     return Entries;
     89   }
     90 
     91   /// layout - Computes the final table layout.
     92   void layout() {
     93     assert(Entries == 0 && "Can only call layout() once");
     94     // Lay out the table in Seqs iteration order.
     95     for (typename SeqMap::iterator I = Seqs.begin(), E = Seqs.end(); I != E;
     96          ++I) {
     97       I->second = Entries;
     98       // Include space for a terminator.
     99       Entries += I->first.size() + 1;
    100     }
    101   }
    102 
    103   /// get - Returns the offset of Seq in the final table.
    104   unsigned get(const SeqT &Seq) const {
    105     assert(Entries && "Call layout() before get()");
    106     typename SeqMap::const_iterator I = Seqs.lower_bound(Seq);
    107     assert(I != Seqs.end() && isSuffix(Seq, I->first) &&
    108            "get() called with sequence that wasn't added first");
    109     return I->second + (I->first.size() - Seq.size());
    110   }
    111 
    112   /// emit - Print out the table as the body of an array initializer.
    113   /// Use the Print function to print elements.
    114   void emit(raw_ostream &OS,
    115             void (*Print)(raw_ostream&, ElemT),
    116             const char *Term = "0") const {
    117     assert(Entries && "Call layout() before emit()");
    118     for (typename SeqMap::const_iterator I = Seqs.begin(), E = Seqs.end();
    119          I != E; ++I) {
    120       OS << "  /* " << I->second << " */ ";
    121       for (typename SeqT::const_iterator SI = I->first.begin(),
    122              SE = I->first.end(); SI != SE; ++SI) {
    123         Print(OS, *SI);
    124         OS << ", ";
    125       }
    126       OS << Term << ",\n";
    127     }
    128   }
    129 };
    130 
    131 // Helper function for SequenceToOffsetTable<string>.
    132 static inline void printChar(raw_ostream &OS, char C) {
    133   unsigned char UC(C);
    134   if (isalnum(UC) || ispunct(UC)) {
    135     OS << '\'';
    136     if (C == '\\' || C == '\'')
    137       OS << '\\';
    138     OS << C << '\'';
    139   } else {
    140     OS << unsigned(UC);
    141   }
    142 }
    143 
    144 } // end namespace llvm
    145 
    146 #endif
    147