StackAllocator.cpp

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/*
    Author : Tobias Stein
    Date   : 22nd October, 2016
    File   : StackAllocator.cpp
 
    Pool allocator.
 
    All Rights Reserved. (c) Copyright 2016.
*/
 
#include "Memory/Allocator/StackAllocator.h"
 
namespace ECS { namespace Memory { namespace Allocator {
 
    StackAllocator::StackAllocator(size_t memSize, const void* mem) :
        IAllocator(memSize, mem)
    {}
 
    StackAllocator::~StackAllocator()
    {
        this->clear();
    }
 
    void* StackAllocator::allocate(size_t memSize, u8 alignment)
    {
        assert(memSize > 0 && "allocate called with memSize = 0.");
 
        union
        {
            void* asVoidPtr;
            uptr asUptr;
            AllocMetaInfo* asMeta;
        };
 
        asVoidPtr = (void*)this->m_MemoryFirstAddress;
 
        // current address
        asUptr += this->m_MemoryUsed;
 
        u8 adjustment = GetAdjustment(asVoidPtr, alignment, sizeof(AllocMetaInfo));
 
        // check if there is enough memory available
        if (this->m_MemoryUsed + memSize + adjustment > this->m_MemorySize)
        {
            // not enough memory
            return nullptr;
        }
 
        // store alignment in allocation meta info
        asMeta->adjustment = adjustment;
 
        // determine aligned memory address
        asUptr += adjustment;
 
        // update book keeping
        this->m_MemoryUsed += memSize + adjustment;
        this->m_MemoryAllocations++;
 
        // return aligned memory address
        return asVoidPtr;
    }
 
    void StackAllocator::free(void* mem)
    {
        union
        {
            void* asVoidPtr;
            uptr asUptr;
            AllocMetaInfo* asMeta;
        };
 
        asVoidPtr = mem;
        
        // get meta info
        asUptr -= sizeof(AllocMetaInfo);
 
        // free used memory
        this->m_MemoryUsed -= ((uptr)this->m_MemoryFirstAddress + this->m_MemoryUsed) - ((uptr)mem + asMeta->adjustment);
            
        // decrement allocation count
        this->m_MemoryAllocations--;
    }
 
    void StackAllocator::clear()
    {
        // simply reset memory
        this->m_MemoryUsed = 0;
        this->m_MemoryAllocations = 0;
    }
 
} } } // namespace ECS::Memory::Allocator