RewriteRope.h

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//===- RewriteRope.h - Rope specialized for rewriter ------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
//  This file defines the RewriteRope class, which is a powerful string class.
//
//===----------------------------------------------------------------------===//
 
#ifndef LLVM_ADT_REWRITEROPE_H
#define LLVM_ADT_REWRITEROPE_H
 
#include "llvm/ADT/IntrusiveRefCntPtr.h"
#include "llvm/ADT/StringRef.h"
#include <cassert>
#include <cstddef>
#include <iterator>
#include <utility>
 
namespace llvm {
 
//===--------------------------------------------------------------------===//
// RopeRefCountString Class
//===--------------------------------------------------------------------===//
 
/// RopeRefCountString - This struct is allocated with 'new char[]' from the
/// heap, and represents a reference counted chunk of string data.  When its
/// ref count drops to zero, it is delete[]'d.  This is primarily managed
/// through the RopePiece class below.
struct RopeRefCountString {
  unsigned RefCount;
  char Data[1]; //  Variable sized.
 
  void Retain() { ++RefCount; }
 
  void Release() {
    assert(RefCount > 0 && "Reference count is already zero.");
    if (--RefCount == 0)
      delete[] (char *)this;
  }
};
 
//===--------------------------------------------------------------------===//
// RopePiece Class
//===--------------------------------------------------------------------===//
 
/// RopePiece - This class represents a view into a RopeRefCountString object.
/// This allows references to string data to be efficiently chopped up and
/// moved around without having to push around the string data itself.
///
/// For example, we could have a 1M RopePiece and want to insert something
/// into the middle of it.  To do this, we split it into two RopePiece objects
/// that both refer to the same underlying RopeRefCountString (just with
/// different offsets) which is a nice constant time operation.
struct RopePiece {
  llvm::IntrusiveRefCntPtr<RopeRefCountString> StrData;
  unsigned StartOffs = 0;
  unsigned EndOffs = 0;
 
  RopePiece() = default;
  RopePiece(llvm::IntrusiveRefCntPtr<RopeRefCountString> Str, unsigned Start,
            unsigned End)
      : StrData(std::move(Str)), StartOffs(Start), EndOffs(End) {}
 
  const char &operator[](unsigned Offset) const {
    return StrData->Data[Offset + StartOffs];
  }
  char &operator[](unsigned Offset) {
    return StrData->Data[Offset + StartOffs];
  }
 
  unsigned size() const { return EndOffs - StartOffs; }
};
 
//===--------------------------------------------------------------------===//
// RopePieceBTreeIterator Class
//===--------------------------------------------------------------------===//
 
/// RopePieceBTreeIterator - This class provides read-only forward iteration
/// over bytes that are in a RopePieceBTree.  This first iterates over bytes
/// in a RopePiece, then iterates over RopePiece's in a RopePieceBTreeLeaf,
/// then iterates over RopePieceBTreeLeaf's in a RopePieceBTree.
class RopePieceBTreeIterator {
  /// CurNode - The current B+Tree node that we are inspecting.
  const void /*RopePieceBTreeLeaf*/ *CurNode = nullptr;
 
  /// CurPiece - The current RopePiece in the B+Tree node that we're
  /// inspecting.
  const RopePiece *CurPiece = nullptr;
 
  /// CurChar - The current byte in the RopePiece we are pointing to.
  unsigned CurChar = 0;
 
public:
  using iterator_category = std::forward_iterator_tag;
  using value_type = const char;
  using difference_type = std::ptrdiff_t;
  using pointer = value_type *;
  using reference = value_type &;
 
  RopePieceBTreeIterator() = default;
  RopePieceBTreeIterator(const void /*RopePieceBTreeNode*/ *N);
 
  char operator*() const { return (*CurPiece)[CurChar]; }
 
  bool operator==(const RopePieceBTreeIterator &RHS) const {
    return CurPiece == RHS.CurPiece && CurChar == RHS.CurChar;
  }
  bool operator!=(const RopePieceBTreeIterator &RHS) const {
    return !operator==(RHS);
  }
 
  RopePieceBTreeIterator &operator++() { // Preincrement
    if (CurChar + 1 < CurPiece->size())
      ++CurChar;
    else
      MoveToNextPiece();
    return *this;
  }
 
  RopePieceBTreeIterator operator++(int) { // Postincrement
    RopePieceBTreeIterator tmp = *this;
    ++*this;
    return tmp;
  }
 
  llvm::StringRef piece() const {
    return llvm::StringRef(&(*CurPiece)[0], CurPiece->size());
  }
 
  void MoveToNextPiece();
};
 
//===--------------------------------------------------------------------===//
// RopePieceBTree Class
//===--------------------------------------------------------------------===//
 
class RopePieceBTree {
  void /*RopePieceBTreeNode*/ *Root;
 
public:
  RopePieceBTree();
  RopePieceBTree(const RopePieceBTree &RHS);
  RopePieceBTree &operator=(const RopePieceBTree &) = delete;
  ~RopePieceBTree();
 
  using iterator = RopePieceBTreeIterator;
 
  iterator begin() const { return iterator(Root); }
  iterator end() const { return iterator(); }
  unsigned size() const;
  unsigned empty() const { return size() == 0; }
 
  void clear();
 
  void insert(unsigned Offset, const RopePiece &R);
 
  void erase(unsigned Offset, unsigned NumBytes);
};
 
//===--------------------------------------------------------------------===//
// RewriteRope Class
//===--------------------------------------------------------------------===//
 
/// RewriteRope - A powerful string class.  This class supports extremely
/// efficient insertions and deletions into the middle of it, even for
/// ridiculously long strings.
class RewriteRope {
  RopePieceBTree Chunks;
 
  /// We allocate space for string data out of a buffer of size AllocChunkSize.
  /// This keeps track of how much space is left.
  llvm::IntrusiveRefCntPtr<RopeRefCountString> AllocBuffer;
  enum { AllocChunkSize = 4080 };
  unsigned AllocOffs = AllocChunkSize;
 
public:
  RewriteRope() = default;
  RewriteRope(const RewriteRope &RHS) : Chunks(RHS.Chunks) {}
 
  // The copy assignment operator is defined as deleted pending further
  // motivation.
  RewriteRope &operator=(const RewriteRope &) = delete;
 
  using iterator = RopePieceBTree::iterator;
  using const_iterator = RopePieceBTree::iterator;
 
  iterator begin() const { return Chunks.begin(); }
  iterator end() const { return Chunks.end(); }
  unsigned size() const { return Chunks.size(); }
 
  void clear() { Chunks.clear(); }
 
  void assign(const char *Start, const char *End) {
    clear();
    if (Start != End)
      Chunks.insert(0, MakeRopeString(Start, End));
  }
 
  void insert(unsigned Offset, const char *Start, const char *End) {
    assert(Offset <= size() && "Invalid position to insert!");
    if (Start == End)
      return;
    Chunks.insert(Offset, MakeRopeString(Start, End));
  }
 
  void erase(unsigned Offset, unsigned NumBytes) {
    assert(Offset + NumBytes <= size() && "Invalid region to erase!");
    if (NumBytes == 0)
      return;
    Chunks.erase(Offset, NumBytes);
  }
 
private:
  RopePiece MakeRopeString(const char *Start, const char *End);
};
 
} // namespace llvm
 
#endif // LLVM_ADT_REWRITEROPE_H