github.com/cellofellow/gopkg@v0.0.0-20140722061823-eec0544a62ad/database/leveldb.chai2010/include/leveldb/slice.h (about)

     1  // Copyright (c) 2011 The LevelDB Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style license that can be
     3  // found in the LICENSE file. See the AUTHORS file for names of contributors.
     4  //
     5  // Slice is a simple structure containing a pointer into some external
     6  // storage and a size.  The user of a Slice must ensure that the slice
     7  // is not used after the corresponding external storage has been
     8  // deallocated.
     9  //
    10  // Multiple threads can invoke const methods on a Slice without
    11  // external synchronization, but if any of the threads may call a
    12  // non-const method, all threads accessing the same Slice must use
    13  // external synchronization.
    14  
    15  #ifndef STORAGE_LEVELDB_INCLUDE_SLICE_H_
    16  #define STORAGE_LEVELDB_INCLUDE_SLICE_H_
    17  
    18  #include <assert.h>
    19  #include <stddef.h>
    20  #include <string.h>
    21  #include <string>
    22  
    23  namespace leveldb {
    24  
    25  class Slice {
    26   public:
    27    // Create an empty slice.
    28    Slice() : data_(""), size_(0) { }
    29  
    30    // Create a slice that refers to d[0,n-1].
    31    Slice(const char* d, size_t n) : data_(d), size_(n) { }
    32  
    33    // Create a slice that refers to the contents of "s"
    34    Slice(const std::string& s) : data_(s.data()), size_(s.size()) { }
    35  
    36    // Create a slice that refers to s[0,strlen(s)-1]
    37    Slice(const char* s) : data_(s), size_(strlen(s)) { }
    38  
    39    // Return a pointer to the beginning of the referenced data
    40    const char* data() const { return data_; }
    41  
    42    // Return the length (in bytes) of the referenced data
    43    size_t size() const { return size_; }
    44  
    45    // Return true iff the length of the referenced data is zero
    46    bool empty() const { return size_ == 0; }
    47  
    48    // Return the ith byte in the referenced data.
    49    // REQUIRES: n < size()
    50    char operator[](size_t n) const {
    51      assert(n < size());
    52      return data_[n];
    53    }
    54  
    55    // Change this slice to refer to an empty array
    56    void clear() { data_ = ""; size_ = 0; }
    57  
    58    // Drop the first "n" bytes from this slice.
    59    void remove_prefix(size_t n) {
    60      assert(n <= size());
    61      data_ += n;
    62      size_ -= n;
    63    }
    64  
    65    // Return a string that contains the copy of the referenced data.
    66    std::string ToString() const { return std::string(data_, size_); }
    67  
    68    // Three-way comparison.  Returns value:
    69    //   <  0 iff "*this" <  "b",
    70    //   == 0 iff "*this" == "b",
    71    //   >  0 iff "*this" >  "b"
    72    int compare(const Slice& b) const;
    73  
    74    // Return true iff "x" is a prefix of "*this"
    75    bool starts_with(const Slice& x) const {
    76      return ((size_ >= x.size_) &&
    77              (memcmp(data_, x.data_, x.size_) == 0));
    78    }
    79  
    80   private:
    81    const char* data_;
    82    size_t size_;
    83  
    84    // Intentionally copyable
    85  };
    86  
    87  inline bool operator==(const Slice& x, const Slice& y) {
    88    return ((x.size() == y.size()) &&
    89            (memcmp(x.data(), y.data(), x.size()) == 0));
    90  }
    91  
    92  inline bool operator!=(const Slice& x, const Slice& y) {
    93    return !(x == y);
    94  }
    95  
    96  inline int Slice::compare(const Slice& b) const {
    97    const int min_len = (size_ < b.size_) ? size_ : b.size_;
    98    int r = memcmp(data_, b.data_, min_len);
    99    if (r == 0) {
   100      if (size_ < b.size_) r = -1;
   101      else if (size_ > b.size_) r = +1;
   102    }
   103    return r;
   104  }
   105  
   106  }  // namespace leveldb
   107  
   108  
   109  #endif  // STORAGE_LEVELDB_INCLUDE_SLICE_H_