4jcraft/Minecraft.Client/Platform/Common/C4JMemoryPool.h

#pragma once

#include <stdlib.h>

class C4JMemoryPool {
public:
    unsigned int Align(unsigned int val, unsigned int align) {
        return int((val + (align - 1)) / align) * align;
    }
    virtual void* Alloc(size_t size) = 0;
    virtual void Free(void* ptr) = 0;
};

// Fast Efficient Fixed-Size Memory Pool : No Loops and No Overhead
// http://www.alogicalmind.com/memory_pools/index.htm
class C4JMemoryPoolFixed : public C4JMemoryPool {
    // Basic type define
    typedef unsigned int uint;
    typedef unsigned char uchar;
    uint m_numOfBlocks;      // Num of blocks
    uint m_sizeOfEachBlock;  // Size of each block
    uint m_numFreeBlocks;    // Num of remaining blocks
    uint m_numInitialized;   // Num of initialized blocks
    uchar* m_memStart;       // Beginning of memory pool
    uchar* m_memEnd;         // End of memory pool
    uchar* m_next;           // Num of next free block
public:
    C4JMemoryPoolFixed() {
        m_numOfBlocks = 0;
        m_sizeOfEachBlock = 0;
        m_numFreeBlocks = 0;
        m_numInitialized = 0;
        m_memStart = nullptr;
        m_memEnd = nullptr;
        m_next = 0;
    }

    C4JMemoryPoolFixed(uint sizeOfEachBlock, uint numOfBlocks) {
        CreatePool(sizeOfEachBlock, numOfBlocks);
    }

    ~C4JMemoryPoolFixed() { DestroyPool(); }

    void CreatePool(uint sizeOfEachBlock, uint numOfBlocks) {
        assert(sizeOfEachBlock >=
               4);  // has to be at least the size of an int, for book keeping
        m_numOfBlocks = numOfBlocks;
        m_sizeOfEachBlock = sizeOfEachBlock;
        m_numFreeBlocks = numOfBlocks;
        m_numInitialized = 0;
        m_memStart = new uchar[m_sizeOfEachBlock * m_numOfBlocks];
        m_memEnd = m_memStart + (m_sizeOfEachBlock * m_numOfBlocks);
        m_next = m_memStart;
    }

    void DestroyPool() {
        delete[] m_memStart;
        m_memStart = nullptr;
    }

    uchar* AddrFromIndex(uint i) const {
        return m_memStart + (i * m_sizeOfEachBlock);
    }

    uint IndexFromAddr(const uchar* p) const {
        return (((uint)(p - m_memStart)) / m_sizeOfEachBlock);
    }

    virtual void* Alloc(size_t size) {
        if (size > m_sizeOfEachBlock) return ::malloc(size);
        if (m_numInitialized < m_numOfBlocks) {
            uint* p = (uint*)AddrFromIndex(m_numInitialized);
            *p = m_numInitialized + 1;
            m_numInitialized++;
        }
        void* ret = nullptr;
        if (m_numFreeBlocks > 0) {
            ret = (void*)m_next;
            --m_numFreeBlocks;
            if (m_numFreeBlocks != 0) {
                m_next = AddrFromIndex(*((uint*)m_next));
            } else {
                m_next = nullptr;
            }
        }
        return ret;
    }

    virtual void Free(void* ptr) {
        if (ptr < m_memStart || ptr > m_memEnd) {
            ::free(ptr);
            return;
        }
        if (m_next != nullptr) {
            (*(uint*)ptr) = IndexFromAddr(m_next);
            m_next = (uchar*)ptr;
        } else {
            *((uint*)ptr) = m_numOfBlocks;
            m_next = (uchar*)ptr;
        }
        ++m_numFreeBlocks;
    }
};  // End pool class

// this pool will constantly grow until it is reset (automatically when all
// allocs have been "freed")
class C4JMemoryPoolGrow : public C4JMemoryPool {
    uint32_t m_totalSize;
    uint32_t m_memUsed;
    uint32_t m_numAllocations;
    uint8_t* m_pMemory;
    uint32_t m_currentOffset;

public:
    C4JMemoryPoolGrow(uint32_t size = 64 * 1024) {
        size = Align(size, 4);
        m_totalSize = size;
        m_pMemory = new uint8_t[size];
        m_currentOffset = 0;
        m_memUsed = 0;
        m_numAllocations = 0;
    }

    virtual void* Alloc(size_t size) {
        size = Align(size, 4);  // 4 byte align the memory
        assert((m_currentOffset + size) <
               m_totalSize);  // make sure we haven't ran out of space
        void* returnMem =
            &m_pMemory[m_currentOffset];  // grab the return memory
        m_currentOffset += size;
        m_numAllocations++;
        return returnMem;
    }
    virtual void Free(void* ptr) {
        m_numAllocations--;
        if (m_numAllocations == 0)
            m_currentOffset =
                0;  // reset the pool when we reach zero allocations
    }
};