src/misc/fixedsizearray.hpp

   1 /*
   2  * This file is part of OpenTTD.
   3  * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
   4  * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
   5  * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
   6  */
   7
   8 /** @file fixedsizearray.hpp A fixed size array that doesn't create items until needed. */
   9
  10 #ifndef FIXEDSIZEARRAY_HPP
  11 #define FIXEDSIZEARRAY_HPP
  12
  13 #include "../core/alloc_func.hpp"
  14
  15 /**
  16  * fixed size array
  17  *  Upon construction it preallocates fixed size block of memory
  18  *  for all items, but doesn't construct them. Item's construction
  19  *  is delayed.
  20  */
  21 template <class T, uint C>
  22 struct FixedSizeArray {
  23 protected:
  24         /** header for fixed size array */
  25         struct ArrayHeader
  26         {
  27                 uint items;           ///< number of items in the array
  28                 uint reference_count; ///< block reference counter (used by copy constructor and by destructor)
  29         };
  30
  31         /* make constants visible from outside */
  32         static const uint Tsize = sizeof(T);                ///< size of item
  33         static const uint HeaderSize = sizeof(ArrayHeader); ///< size of header
  34
  35         /**
  36          * the only member of fixed size array is pointer to the block
  37          *  of C array of items. Header can be found on the offset -sizeof(ArrayHeader).
  38          */
  39         T *data;
  40
  41         /** return reference to the array header (non-const) */
  42         inline ArrayHeader &Hdr()
  43         {
  44                 return *(ArrayHeader*)(((byte*)data) - HeaderSize);
  45         }
  46
  47         /** return reference to the array header (const) */
  48         inline const ArrayHeader &Hdr() const
  49         {
  50                 return *(ArrayHeader*)(((byte*)data) - HeaderSize);
  51         }
  52
  53         /** return reference to the block reference counter */
  54         inline uint &RefCnt()
  55         {
  56                 return Hdr().reference_count;
  57         }
  58
  59         /** return reference to number of used items */
  60         inline uint &SizeRef()
  61         {
  62                 return Hdr().items;
  63         }
  64
  65 public:
  66         /** Default constructor. Preallocate space for items and header, then initialize header. */
  67         FixedSizeArray()
  68         {
  69                 /* Ensure the size won't overflow. */
  70                 static_assert(C < (SIZE_MAX - HeaderSize) / Tsize);
  71
  72                 /* allocate block for header + items (don't construct items) */
  73                 data = (T*)((MallocT<byte>(HeaderSize + C * Tsize)) + HeaderSize);
  74                 SizeRef() = 0; // initial number of items
  75                 RefCnt() = 1; // initial reference counter
  76         }
  77
  78         /** Copy constructor. Preallocate space for items and header, then initialize header. */
  79         FixedSizeArray(const FixedSizeArray<T, C> &src)
  80         {
  81                 /* share block (header + items) with the source array */
  82                 data = src.data;
  83                 RefCnt()++; // now we share block with the source
  84         }
  85
  86         /** destroy remaining items and free the memory block */
  87         ~FixedSizeArray()
  88         {
  89                 /* release one reference to the shared block */
  90                 if ((--RefCnt()) > 0) return; // and return if there is still some owner
  91
  92                 Clear();
  93                 /* free the memory block occupied by items */
  94                 free(((byte*)data) - HeaderSize);
  95                 data = nullptr;
  96         }
  97
  98         /** Clear (destroy) all items */
  99         inline void Clear()
 100         {
 101                 /* Walk through all allocated items backward and destroy them
 102                  * Note: this->Length() can be zero. In that case data[this->Length() - 1] is evaluated unsigned
 103                  *       on some compilers with some architectures. (e.g. gcc with x86) */
 104                 for (T *pItem = this->data + this->Length() - 1; pItem >= this->data; pItem--) {
 105                         pItem->~T();
 106                 }
 107                 /* number of items become zero */
 108                 SizeRef() = 0;
 109         }
 110
 111         /** return number of used items */
 112         inline uint Length() const
 113         {
 114                 return Hdr().items;
 115         }
 116
 117         /** return true if array is full */
 118         inline bool IsFull() const
 119         {
 120                 return Length() >= C;
 121         }
 122
 123         /** return true if array is empty */
 124         inline bool IsEmpty() const
 125         {
 126                 return Length() <= 0;
 127         }
 128
 129         /** add (allocate), but don't construct item */
 130         inline T *Append()
 131         {
 132                 assert(!IsFull());
 133                 return &data[SizeRef()++];
 134         }
 135
 136         /** add and construct item using default constructor */
 137         inline T *AppendC()
 138         {
 139                 T *item = Append();
 140                 new(item)T;
 141                 return item;
 142         }
 143         /** return item by index (non-const version) */
 144         inline T& operator[](uint index)
 145         {
 146                 assert(index < Length());
 147                 return data[index];
 148         }
 149
 150         /** return item by index (const version) */
 151         inline const T& operator[](uint index) const
 152         {
 153                 assert(index < Length());
 154                 return data[index];
 155         }
 156 };
 157
 158 #endif /* FIXEDSIZEARRAY_HPP */