rangeallocator.h

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#pragma once
//------------------------------------------------------------------------------
//------------------------------------------------------------------------------
#include "core/types.h"
#include "util/bit.h"
#include "util/array.h"
#include <utility>
 
namespace Memory
{
 
//------------------------------------------------------------------------------
struct RangeAllocation
{
    size_t offset;
    size_t size;
    uint node;
 
    static constexpr size_t OOM = 0xFFFFFFFF;
};
 
//------------------------------------------------------------------------------
class RangeAllocator
{
public:
    RangeAllocator();
    RangeAllocator(size_t size, SizeT maxNumAllocs);
    ~RangeAllocator();

    void Clear();

    bool Empty();

    RangeAllocation Alloc(size_t size, size_t alignment = 1);
    void Dealloc(const RangeAllocation& allocation);
 
private:
    uint InsertNode(size_t size, size_t offset);
    void RemoveNode(uint nodeIndex);
 
    struct RangeAllocatorNode
    {
        RangeAllocatorNode() :
            resident(false)
            , size(0)
            , offset(0)
            , binPrev(END)
            , binNext(END)
            , blockPrev(END)
            , blockNext(END)
        {};
        bool resident;
        size_t size;
        size_t offset;
 
        static constexpr uint END = 0xFFFFFFFF;
        uint binPrev, binNext;
        uint blockPrev, blockNext;
    };
 
    struct BinIndex
    {
        BinIndex() : bin(0), bucket(0) {};
        uint bin;
        uint bucket;
        uint index;
    };

    static BinIndex IndexFromSize(size_t size, bool round = false);
    static uint BucketFromSize(size_t size);
    static uint BinFromSize(uint size, uint bucket);
 
public:
    size_t size;
    size_t freeStorage;
    uint freeNodeIterator;
    uint numAllocs;
 
    static constexpr uint NUM_BUCKETS = 32u;
    static constexpr uint NUM_BINS_PER_BUCKET = 8u;
 
 
    uint bucketUsageMask;
    uint binMasks[NUM_BUCKETS];
    uint binHeads[NUM_BUCKETS * NUM_BINS_PER_BUCKET];
 
    Util::Array<RangeAllocatorNode> nodes;
    Util::Array<uint> freeNodes;
};
 
 
static constexpr uint BUCKET_INDEX_SHIFT = 3u;
static constexpr uint BIN_INDEX_MASK = 0x7;
 
//------------------------------------------------------------------------------
inline 
RangeAllocator::RangeAllocator()
    : RangeAllocator(0,0)
{
}
 
//------------------------------------------------------------------------------
inline
RangeAllocator::RangeAllocator(size_t size, SizeT maxNumAllocs)
{   
    this->size = size;
    this->freeNodes.Resize(maxNumAllocs + 1);
    this->nodes.Resize(maxNumAllocs + 1);
    this->numAllocs = 0;
 
    // Clear the allocator
    this->Clear();
}
 
//------------------------------------------------------------------------------
inline 
RangeAllocator::~RangeAllocator()
{
}
 
//------------------------------------------------------------------------------
inline void 
RangeAllocator::Clear()
{
    // Reset bit masks
    this->bucketUsageMask = 0x0;
    this->numAllocs = 0;
    memset(this->binMasks, 0x0, sizeof(this->binMasks));
 
    // Reset bin heads
    for (uint i = 0; i < NUM_BUCKETS * NUM_BINS_PER_BUCKET; i++)
    {
        this->binHeads[i] = RangeAllocatorNode::END;
    }
 
    // Clear nodes
    for (uint i = 0; i < this->nodes.Size(); i++)
    {
        this->nodes[i] = RangeAllocatorNode();
        this->freeNodes[i] = this->nodes.Size() - i - 1;
    }
    this->freeNodeIterator = this->nodes.Size() - 1;
    this->freeStorage = 0;
 
    // Insert node covering the whole range
    if (this->size > 0)
        this->InsertNode(this->size, 0);
}
 
//------------------------------------------------------------------------------
inline bool 
RangeAllocator::Empty()
{
    return this->freeStorage == this->size;
}
 
//------------------------------------------------------------------------------
inline uint
FindLowestSetBitAfter(uint bitMask, uint startBitIndex)
{
    uint maskBeforeStartIndex = (1 << startBitIndex) - 1;
    uint maskAfterStartIndex = ~maskBeforeStartIndex;
    uint bitsAfter = bitMask & maskAfterStartIndex;
    if (bitsAfter == 0) return RangeAllocation::OOM;
    return Util::CountTrailingZeroes(bitsAfter);
}
 
//------------------------------------------------------------------------------
inline RangeAllocation 
RangeAllocator::Alloc(size_t size, size_t alignment)
{
    // We are not allowed any more allocations
    size_t alignedSize = size + alignment - 1;
    if (this->freeStorage < alignedSize || this->freeNodeIterator == RangeAllocation::OOM)
    {
        return RangeAllocation{ .offset = RangeAllocation::OOM, .size = 0, .node = RangeAllocatorNode::END };
    }
 
    BinIndex minIndex = IndexFromSize(alignedSize, true);
    uint bin = RangeAllocation::OOM;
    uint bucket = minIndex.bucket;
 
    if (this->bucketUsageMask & (1 << bucket))
    {
        bin = FindLowestSetBitAfter(this->binMasks[bucket], minIndex.bin);
    }
 
    if (bin == RangeAllocation::OOM)
    {
        // Find next bit set after bucket in the usage mask
        bucket = FindLowestSetBitAfter(this->bucketUsageMask, bucket + 1);
 
        // If this means we get 32, it means we're out of buckets that fit
        if (bucket == RangeAllocation::OOM)
        {
            return RangeAllocation{ .offset = RangeAllocation::OOM, .size = 0, .node = RangeAllocatorNode::END };
        }
 
        // Find any bit, since this bucket has to fit
        bin = Util::CountTrailingZeroes(this->binMasks[bucket]);
    }
 
    BinIndex binIndex;
    binIndex.bucket = bucket;
    binIndex.bin = bin;
    uint16_t index = (bucket << BUCKET_INDEX_SHIFT) | bin;
 
    // Get linked list head
    uint nodeIndex = this->binHeads[index];
    RangeAllocatorNode& node = this->nodes[nodeIndex];
    n_assert(!node.resident);
 
    // Save total size of node
    size_t totalSize = node.size;
    //n_assert(totalSize >= alignedSize);
    size_t alignedOffset = Memory::align(node.offset, (size_t)alignment);
    node.size = alignedSize;
    node.resident = true;
    this->numAllocs++;
 
    // Bump head of bin to next node
    this->binHeads[index] = node.binNext;
    if (node.binNext != RangeAllocatorNode::END)
        this->nodes[node.binNext].binPrev = RangeAllocatorNode::END;
 
    // If bin head is empty after we grab the node, unmark the bin
    if (this->binHeads[index] == RangeAllocatorNode::END)
    {
        this->binMasks[binIndex.bucket] &= ~(1 << binIndex.bin);
 
        // If all bins are busy, unmark the bucket bits
        if (this->binMasks[binIndex.bucket] == 0)
        {
            this->bucketUsageMask &= ~(1 << binIndex.bucket);
        }
    }
 
    // We subtract the entire size of the node
    this->freeStorage -= totalSize;
    
    // The remainder in the front is then added back
    size_t remainder = totalSize - node.size;
    if (remainder > 0ull)
    {
        uint newNodeIndex = this->InsertNode(remainder, node.offset + node.size);
        if (newNodeIndex != RangeAllocatorNode::END)
        {
            RangeAllocatorNode& newNode = this->nodes[newNodeIndex];
 
            // If the current node has a next, repoint it to the new block
            if (node.blockNext != RangeAllocatorNode::END)
            {
                this->nodes[node.blockNext].blockPrev = newNodeIndex;
            }
 
            newNode.blockPrev = nodeIndex;
            newNode.blockNext = node.blockNext;
            node.blockNext = newNodeIndex;
            n_assert((this->nodes[nodeIndex].offset + this->nodes[nodeIndex].size) == newNode.offset);
        }
    }
    
    return RangeAllocation{ .offset = alignedOffset, .size = alignedSize, .node = nodeIndex };
}
 
//------------------------------------------------------------------------------
inline void 
RangeAllocator::Dealloc(const RangeAllocation& allocation)
{
    RangeAllocatorNode& node = this->nodes[allocation.node];
    n_assert(node.resident);
    node.resident = false;
    this->numAllocs--;
    size_t size = node.size;
    size_t offset = node.offset;
 
    // Try to merge with left
    if (node.blockPrev != RangeAllocatorNode::END)
    {
        RangeAllocatorNode& prev = this->nodes[node.blockPrev];
        if (!prev.resident)
        {
            offset = prev.offset;
            size += prev.size;
 
            this->RemoveNode(node.blockPrev);
            n_assert(prev.blockNext == allocation.node);
            node.blockPrev = prev.blockPrev;
        }
    }
 
    if (node.blockNext != RangeAllocatorNode::END)
    {
        RangeAllocatorNode& next = this->nodes[node.blockNext];
        if (!next.resident)
        {
            size += next.size;
            this->RemoveNode(node.blockNext);
            n_assert(next.blockPrev == allocation.node);
            node.blockNext = next.blockNext;
        }
    }
 
 
    uint leftNode = node.blockPrev;
    uint rightNode = node.blockNext;
    this->freeNodes[++this->freeNodeIterator] = allocation.node;
 
    // Add merged node
    uint mergedNode = this->InsertNode(size, offset);
 
    // Connect adjacent nodes with newly inserted node
    if (leftNode != RangeAllocatorNode::END)
    {
        this->nodes[mergedNode].blockPrev = leftNode;
        this->nodes[leftNode].blockNext = mergedNode;
    }
 
    if (rightNode != RangeAllocatorNode::END)
    {
        this->nodes[mergedNode].blockNext = rightNode;
        this->nodes[rightNode].blockPrev = mergedNode;
    }
}
 
//------------------------------------------------------------------------------
inline uint 
RangeAllocator::InsertNode(size_t size, size_t offset)
{
    if (this->freeNodeIterator == 0xFFFFFFFF)
        return RangeAllocatorNode::END;
 
    BinIndex binIndex = IndexFromSize(size);
    uint16_t index = binIndex.index;
 
    if (this->binHeads[index] == RangeAllocatorNode::END)
    {
        // Bin isn't used, flip bit for bucket and bin
        this->binMasks[binIndex.bucket] |= (1 << binIndex.bin);
        this->bucketUsageMask |= (1 << binIndex.bucket);
    }
 
    // Get new node
    uint headNodeIndex = this->binHeads[index];
    uint newNodeIndex = this->freeNodes[this->freeNodeIterator--];
    RangeAllocatorNode& newNode = this->nodes[newNodeIndex];
    n_assert(!newNode.resident);
 
    // Set the size and offset of the node memory
    newNode.size = size;
    newNode.offset = offset;
    newNode.binNext = headNodeIndex;
    newNode.binPrev = RangeAllocatorNode::END;
    newNode.blockNext = RangeAllocatorNode::END;
    newNode.blockPrev = RangeAllocatorNode::END;
    newNode.resident = false;
 
    this->freeStorage += size;
 
    // Get node at head of bin
    if (headNodeIndex != RangeAllocatorNode::END)
    {
        // If valid, repoint head node to point to the new node in the bin
        RangeAllocatorNode& headNode = this->nodes[headNodeIndex];
        headNode.binPrev = newNodeIndex;
    }
    this->binHeads[index] = newNodeIndex;
 
    return newNodeIndex;
}
 
//------------------------------------------------------------------------------
inline void 
RangeAllocator::RemoveNode(uint nodeIndex)
{
    // Get node to free
    RangeAllocatorNode& node = this->nodes[nodeIndex];
    node.resident = false;
 
    // Add back the storage to the allocator
    this->freeStorage -= node.size;
    
    if (node.binPrev == RangeAllocatorNode::END)
    {
        BinIndex binIndex = IndexFromSize(node.size);
        uint16_t index = binIndex.index;
 
        // Point head of 
        this->binHeads[index] = node.binNext;
        if (node.binNext != RangeAllocatorNode::END)
        {
            this->nodes[node.binNext].binPrev = RangeAllocatorNode::END;
        }
 
        if (node.binNext == RangeAllocatorNode::END)
        {
            n_assert(this->binMasks[binIndex.bucket] != 0x0);
            // If we are deleting the last node, make sure to unmark the bin
            this->binMasks[binIndex.bucket] &= ~(1 << binIndex.bin);
 
            if (this->binMasks[binIndex.bucket] == 0x0)
            {
                // If all bins have been cleared, clear the entire bucket
                this->bucketUsageMask &= ~(1 << binIndex.bucket);
            }
        }
    } 
    else
    {
        this->nodes[node.binPrev].binNext = node.binNext;
        if (node.binNext != RangeAllocatorNode::END)
        {
            this->nodes[node.binNext].binPrev = node.binPrev;
        }
    }
 
    this->freeNodes[++this->freeNodeIterator] = nodeIndex;
}
 
static constexpr uint MANTISSA_BITS = 3;
static constexpr uint MANTISSA_VALUE = 1 << MANTISSA_BITS;
static constexpr uint MANTISSA_MASK = MANTISSA_VALUE - 1;
 
 
//------------------------------------------------------------------------------
inline uint
BinMaskRoundedUp(size_t size)
{
    uint exp = 0;
    uint mantissa = 0;
 
    if (size < MANTISSA_VALUE)
    {
        // Denorm: 0..(MANTISSA_VALUE-1)
        mantissa = (uint)size;
    }
    else
    {
        // Normalized: Hidden high bit always 1. Not stored. Just like float.
        uint highestSetBit = Util::LastBitSetIndex(size);
 
        uint mantissaStartBit = highestSetBit - MANTISSA_BITS;
        exp = mantissaStartBit + 1;
        mantissa = (size >> mantissaStartBit) & MANTISSA_MASK;
 
        size_t lowBitsMask = (1 << mantissaStartBit) - 1;
 
        // Round up!
        if ((size & lowBitsMask) != 0)
            mantissa++;
    }
 
    return (exp << MANTISSA_BITS) + mantissa; // + allows mantissa->exp overflow for round up
}
 
//------------------------------------------------------------------------------
inline uint
BinMask(size_t size)
{
    uint exp = 0;
    uint mantissa = 0;
 
    if (size < MANTISSA_VALUE)
    {
        // Denorm: 0..(MANTISSA_VALUE-1)
        mantissa = (uint)size;
    }
    else
    {
        // Normalized: Hidden high bit always 1. Not stored. Just like float.
        uint highestSetBit = Util::LastBitSetIndex(size);
 
        uint mantissaStartBit = highestSetBit - MANTISSA_BITS;
        exp = mantissaStartBit + 1;
        mantissa = (size >> mantissaStartBit) & MANTISSA_MASK;
    }
 
    return (exp << MANTISSA_BITS) | mantissa;
}
 
//------------------------------------------------------------------------------
inline uint 
RangeAllocator::BinFromSize(uint size, uint bucket)
{
    n_assert(size < (1 << bucket));
    uint mask = (size >> (bucket - 4)) & (NUM_BINS_PER_BUCKET - 1u);
    return mask;
}
 
//------------------------------------------------------------------------------
inline RangeAllocator::BinIndex
RangeAllocator::IndexFromSize(size_t size, bool round)
{
    RangeAllocator::BinIndex ret;
    uint index;
    if (round)
        index = BinMaskRoundedUp(size);
    else
        index = BinMask(size);
    ret.bucket = index >> BUCKET_INDEX_SHIFT;
    ret.bin = index & BIN_INDEX_MASK;
    ret.index = index;
    return ret;
}
 
} // namespace Memory