stack.h

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#ifndef RAPIDJSON_INTERNAL_STACK_H_
#define RAPIDJSON_INTERNAL_STACK_H_

namespace rapidjson {
namespace internal {

// Stack


template <typename Allocator>
class Stack {
public:
   Stack(Allocator* allocator, size_t stack_capacity) : allocator_(allocator), own_allocator_(0), stack_(0), stack_top_(0), stack_end_(0), stack_capacity_(stack_capacity) {
      RAPIDJSON_ASSERT(stack_capacity_ > 0);
      if (!allocator_)
         own_allocator_ = allocator_ = new Allocator();
      stack_top_ = stack_ = (char*)allocator_->Malloc(stack_capacity_);
      stack_end_ = stack_ + stack_capacity_;
   }

   ~Stack() {
      Allocator::Free(stack_);
      delete own_allocator_; // Only delete if it is owned by the stack
   }

   void Clear() { /*stack_top_ = 0;*/ stack_top_ = stack_; }

   template<typename T>
   T* Push(size_t count = 1) {
       // Expand the stack if needed
      if (stack_top_ + sizeof(T) * count >= stack_end_) {
         size_t new_capacity = stack_capacity_ * 2;
         size_t size = GetSize();
         size_t new_size = GetSize() + sizeof(T) * count;
         if (new_capacity < new_size)
            new_capacity = new_size;
         stack_ = (char*)allocator_->Realloc(stack_, stack_capacity_, new_capacity);
         stack_capacity_ = new_capacity;
         stack_top_ = stack_ + size;
         stack_end_ = stack_ + stack_capacity_;
      }
      T* ret = (T*)stack_top_;
      stack_top_ += sizeof(T) * count;
      return ret;
   }

   template<typename T>
   T* Pop(size_t count) {
      RAPIDJSON_ASSERT(GetSize() >= count * sizeof(T));
      stack_top_ -= count * sizeof(T);
      return (T*)stack_top_;
   }

   template<typename T>
   T* Top() { 
      RAPIDJSON_ASSERT(GetSize() >= sizeof(T));
      return (T*)(stack_top_ - sizeof(T));
   }

   template<typename T>
   T* Bottom() { return (T*)stack_; }

   Allocator& GetAllocator() { return *allocator_; }
   size_t GetSize() const { return stack_top_ - stack_; }
   size_t GetCapacity() const { return stack_capacity_; }

private:
   Allocator* allocator_;
   Allocator* own_allocator_;
   char *stack_;
   char *stack_top_;
   char *stack_end_;
   size_t stack_capacity_;
};

} // namespace internal
} // namespace rapidjson

#endif // RAPIDJSON_STACK_H_