stack.h

#ifndef RAPIDJSON_INTERNAL_STACK_H_
#define RAPIDJSON_INTERNAL_STACK_H_

namespace rapidjson {
namespace internal {

///////////////////////////////////////////////////////////////////////////////
// Stack

//! A type-unsafe stack for storing different types of data.
/*! \tparam Allocator Allocator for allocating stack memory.
*/
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_