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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 TBLGEN_SEQUENCE_TO_OFFSET_TABLE_H
     17 #define TBLGEN_SEQUENCE_TO_OFFSET_TABLE_H
     18 
     19 #include "llvm/Support/raw_ostream.h"
     20 #include <functional>
     21 #include <algorithm>
     22 #include <vector>
     23 #include <cassert>
     24 #include <cctype>
     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 /// @param SeqT The sequence container. (vector or string).
     33 /// @param 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 : public std::binary_function<SeqT, SeqT, bool> {
     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   /// layout - Computes the final table layout.
     85   void layout() {
     86     assert(Entries == 0 && "Can only call layout() once");
     87     // Lay out the table in Seqs iteration order.
     88     for (typename SeqMap::iterator I = Seqs.begin(), E = Seqs.end(); I != E;
     89          ++I) {
     90       I->second = Entries;
     91       // Include space for a terminator.
     92       Entries += I->first.size() + 1;
     93     }
     94   }
     95 
     96   /// get - Returns the offset of Seq in the final table.
     97   unsigned get(const SeqT &Seq) const {
     98     assert(Entries && "Call layout() before get()");
     99     typename SeqMap::const_iterator I = Seqs.lower_bound(Seq);
    100     assert(I != Seqs.end() && isSuffix(Seq, I->first) &&
    101            "get() called with sequence that wasn't added first");
    102     return I->second + (I->first.size() - Seq.size());
    103   }
    104 
    105   /// emit - Print out the table as the body of an array initializer.
    106   /// Use the Print function to print elements.
    107   void emit(raw_ostream &OS,
    108             void (*Print)(raw_ostream&, ElemT),
    109             const char *Term = "0") const {
    110     assert(Entries && "Call layout() before emit()");
    111     for (typename SeqMap::const_iterator I = Seqs.begin(), E = Seqs.end();
    112          I != E; ++I) {
    113       OS << "  /* " << I->second << " */ ";
    114       for (typename SeqT::const_iterator SI = I->first.begin(),
    115              SE = I->first.end(); SI != SE; ++SI) {
    116         Print(OS, *SI);
    117         OS << ", ";
    118       }
    119       OS << Term << ",\n";
    120     }
    121   }
    122 };
    123 
    124 // Helper function for SequenceToOffsetTable<string>.
    125 static inline void printChar(raw_ostream &OS, char C) {
    126   unsigned char UC(C);
    127   if (isalnum(UC) || ispunct(UC)) {
    128     OS << '\'';
    129     if (C == '\\' || C == '\'')
    130       OS << '\\';
    131     OS << C << '\'';
    132   } else {
    133     OS << unsigned(UC);
    134   }
    135 }
    136 
    137 } // end namespace llvm
    138 
    139 #endif
    140