PoolAllocator.cpp

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/*
    Author : Tobias Stein
    Date   : 22nd October, 2016
    File   : PoolAllocator.cpp
 
    Pool allocator.
 
    All Rights Reserved. (c) Copyright 2016.
*/
 
#include "Memory/Allocator/PoolAllocator.h"
 
namespace ECS { namespace Memory { namespace Allocator {
 
    PoolAllocator::PoolAllocator(size_t memSize, const void* mem, size_t objectSize, u8 objectAlignment) :
        IAllocator(memSize, mem),
        OBJECT_SIZE(objectSize),
        OBJECT_ALIGNMENT(objectAlignment)
    {
        this->clear();
    }
 
    PoolAllocator::~PoolAllocator()
    {
        this->freeList = nullptr;
    }
    
 
    void* PoolAllocator::allocate(size_t memSize, u8 alignment)
    {
        assert(memSize > 0 && "allocate called with memSize = 0.");
        assert(memSize == this->OBJECT_SIZE && alignment == this->OBJECT_ALIGNMENT);
 
        if (this->freeList == nullptr)
            return nullptr;
 
        // get free slot
        void* p = this->freeList;
 
        // point to next free slot
        this->freeList = (void**)(*this->freeList);
 
        this->m_MemoryUsed += this->OBJECT_SIZE;
        this->m_MemoryAllocations++;
 
        return p;
    }
 
 
    void PoolAllocator::free(void* mem)
    {
        // put this slot back to free list
        *((void**)mem) = this->freeList;
 
        this->freeList = (void**)mem;
 
        this->m_MemoryUsed -= this->OBJECT_SIZE;
        this->m_MemoryAllocations--;
    }
 
 
    void PoolAllocator::clear()
    {
        u8 adjustment = GetAdjustment(this->m_MemoryFirstAddress, this->OBJECT_ALIGNMENT);
        
        size_t numObjects = (size_t)floor((this->m_MemorySize - adjustment) / this->OBJECT_SIZE);
 
        union
        {
            void* asVoidPtr;
            uptr asUptr;
        };
 
        asVoidPtr = (void*)this->m_MemoryFirstAddress;
 
        // align start address
        asUptr += adjustment;
 
        this->freeList = (void**)asVoidPtr;
 
        void** p = this->freeList;
 
        for (size_t i = 0; i < (numObjects - 1); ++i)
        {
            *p = (void*)((uptr)p + this->OBJECT_SIZE);
 
             p = (void**)*p;
        }
 
        *p = nullptr;
    }
 
}}} // namespace ECS::Memory::Allocator