forked from BilalY/Rasagar
255 lines
10 KiB
C#
255 lines
10 KiB
C#
using System;
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using Unity.Collections;
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using Unity.Collections.LowLevel.Unsafe;
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using Unity.Mathematics;
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using UnityEngine.Assertions;
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namespace UnityEngine.Rendering.Universal
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{
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struct BuddyAllocation
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{
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public int level;
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public int index;
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public BuddyAllocation(int level, int index)
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{
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this.level = level;
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this.index = index;
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}
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public uint2 index2D => SpaceFillingCurves.DecodeMorton2D((uint)index);
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}
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unsafe struct BuddyAllocator : IDisposable
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{
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struct Header
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{
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public int branchingOrder;
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public int levelCount;
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public int allocationCount;
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public int freeAllocationIdsCount;
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}
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// This data structure uses one big allocation containing a fixed header and all the arrays.
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// Some arrays are sub-divided per order, which can be identified by the presence of an X(int order) method,
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// which allows for easy access to the slice of data for the specified order.
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// The offsets for the arrays are stored together with the pointer to avoid a double look-up when
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// accessing data.
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void* m_Data;
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ref Header header => ref UnsafeUtility.AsRef<Header>(m_Data);
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(int, int) m_ActiveFreeMaskCounts;
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NativeArray<int> freeMaskCounts => GetNativeArray<int>(m_ActiveFreeMaskCounts.Item1, m_ActiveFreeMaskCounts.Item2);
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(int, int) m_FreeMasksStorage;
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NativeArray<ulong> freeMasksStorage => GetNativeArray<ulong>(m_FreeMasksStorage.Item1, m_FreeMasksStorage.Item2);
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NativeArray<ulong> FreeMasks(int level) => freeMasksStorage.GetSubArray(LevelOffset64(level, header.branchingOrder), LevelLength64(level, header.branchingOrder));
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(int, int) m_FreeMaskIndicesStorage;
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NativeArray<int> freeMaskIndicesStorage => GetNativeArray<int>(m_FreeMaskIndicesStorage.Item1, m_FreeMaskIndicesStorage.Item2);
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NativeArray<int> FreeMaskIndices(int level) => freeMaskIndicesStorage.GetSubArray(LevelOffset64(level, header.branchingOrder), LevelLength64(level, header.branchingOrder));
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Allocator m_Allocator;
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#if ENABLE_UNITY_COLLECTIONS_CHECKS
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AtomicSafetyHandle m_SafetyHandle;
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#endif
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public int levelCount => header.levelCount;
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public BuddyAllocator(int levelCount, int branchingOrder, Allocator allocator = Allocator.Persistent)
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{
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// Allows us to support 1D, 2D, and 3D cases.
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Assert.IsTrue(branchingOrder is >= 1 and <= 3);
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// Memory usage explodes unless capped like this.
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Assert.IsTrue((levelCount + branchingOrder - 1) / branchingOrder is >= 1 and <= 24);
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var dataSize = sizeof(Header);
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m_ActiveFreeMaskCounts = AllocateRange<int>(levelCount, ref dataSize);
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m_FreeMasksStorage = AllocateRange<ulong>(LevelOffset64(levelCount, branchingOrder), ref dataSize);
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m_FreeMaskIndicesStorage = AllocateRange<int>(LevelOffset64(levelCount, branchingOrder), ref dataSize);
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m_Data = UnsafeUtility.Malloc(dataSize, 64, allocator);
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UnsafeUtility.MemClear(m_Data, dataSize);
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m_Allocator = allocator;
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#if ENABLE_UNITY_COLLECTIONS_CHECKS
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m_SafetyHandle = AtomicSafetyHandle.Create();
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#endif
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header = new Header
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{
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branchingOrder = branchingOrder,
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levelCount = levelCount
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};
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// Initialize level-0 to have 1/1 block available.
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var freeMasks0 = FreeMasks(0);
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freeMasks0[0] = 0b1111;
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var maskCounts = freeMaskCounts;
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maskCounts[0] = 1;
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}
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public bool TryAllocate(int requestedLevel, out BuddyAllocation allocation)
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{
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allocation = default;
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// Find the highest level that has a block available.
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var level = requestedLevel;
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var maskCounts = freeMaskCounts;
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while (level >= 0)
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{
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if (maskCounts[level] > 0) break;
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level--;
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}
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// No blocks available.
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if (level < 0) return false;
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// Split a block at the level we found.
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int dataIndex;
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{
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var freeMaskIndices = FreeMaskIndices(level);
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var maskIndex = freeMaskIndices[--maskCounts[level]];
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var freeMasks = FreeMasks(level);
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var freeMask = freeMasks[maskIndex];
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Assert.AreNotEqual(freeMask, 0);
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var bitIndex = math.tzcnt(freeMask);
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freeMask ^= 1ul << bitIndex;
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freeMasks[maskIndex] = freeMask;
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if (freeMask != 0) freeMaskIndices[maskCounts[level]++] = maskIndex;
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dataIndex = maskIndex * 64 + bitIndex;
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}
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// Walk up the levels until we hit the requested level. For each level we want to mark the remaining parts
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// of the newly split blocks as free.
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while (level < requestedLevel)
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{
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level++;
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dataIndex <<= header.branchingOrder;
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var maskIndex = dataIndex >> 6;
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var bitIndex = dataIndex & 63;
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var freeMasks = FreeMasks(level);
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var freeMask = freeMasks[maskIndex];
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// We might have hit a mask that already contained free blocks. If not, add the mask index to the free list.
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if (freeMask == 0)
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{
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var freeMaskIndices = FreeMaskIndices(level);
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freeMaskIndices[maskCounts[level]++] = maskIndex;
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}
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// Mark other bits in the block we just broke apart as free.
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// In binary form, 2^b will give us a 1 followed by b 0s. So to get b ones, we subtract 1. Since we want
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// the least significant bit to be 0, we subtract another 1.
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// E.g. for branching order 1 we get 10b, for 2 we get 1110b, for 3 we get 11111110b.
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// Finally we shift according to the data index.
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Assert.IsTrue(bitIndex + Pow2(header.branchingOrder) - 1 < 64);
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freeMask |= ((1ul << Pow2(header.branchingOrder)) - 2ul) << bitIndex;
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freeMasks[maskIndex] = freeMask;
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}
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allocation.level = level;
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allocation.index = dataIndex;
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return true;
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}
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public void Free(BuddyAllocation allocation)
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{
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var level = allocation.level;
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var dataIndex = allocation.index;
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while (level >= 0)
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{
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var maskIndex = dataIndex >> 6;
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var bitIndex = dataIndex & 63;
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var freeMasks = FreeMasks(level);
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var freeMask = freeMasks[maskIndex];
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var wasZero = freeMask == 0;
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freeMask |= 1ul << bitIndex;
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var indices = FreeMaskIndices(level);
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var counts = freeMaskCounts;
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var superBlockMask = ((1ul << Pow2(header.branchingOrder)) - 1) << ((bitIndex >> header.branchingOrder) * Pow2(header.branchingOrder));
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// Check if the whole super-block (i.e. making up one block of the next level) is free.
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// If it is, we let the loop continue upwards.
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if (level == 0 || (~freeMask & superBlockMask) != 0)
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{
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freeMasks[maskIndex] = freeMask;
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if (wasZero)
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{
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indices[counts[level]++] = maskIndex;
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}
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break;
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}
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freeMask &= ~superBlockMask;
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freeMasks[maskIndex] = freeMask;
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if (!wasZero && freeMask == 0)
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{
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for (var i = 0; i < indices.Length; i++)
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{
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if (indices[i] == maskIndex)
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{
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indices[i] = indices[--counts[level]];
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break;
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}
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}
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}
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level--;
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dataIndex >>= header.branchingOrder;
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}
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}
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public void Dispose()
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{
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UnsafeUtility.Free(m_Data, m_Allocator);
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#if ENABLE_UNITY_COLLECTIONS_CHECKS
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AtomicSafetyHandle.Release(m_SafetyHandle);
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#endif
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m_Data = default;
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m_Allocator = default;
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}
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NativeArray<T> GetNativeArray<T>(int offset, int length) where T : struct
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{
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var array = NativeArrayUnsafeUtility.ConvertExistingDataToNativeArray<T>(PtrAdd(m_Data, offset), length, m_Allocator);
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#if ENABLE_UNITY_COLLECTIONS_CHECKS
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NativeArrayUnsafeUtility.SetAtomicSafetyHandle(ref array, m_SafetyHandle);
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#endif
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return array;
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}
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// sum x^i for i=0..(n-1) = (x ^ n - 1) / (x - 1) where n is order and n is 2^branchingOrder
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static int LevelOffset(int level, int branchingOrder) => (Pow2(branchingOrder) * (Pow2(branchingOrder * (level - 1) + branchingOrder) - 1)) / (Pow2(branchingOrder) - 1);
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static int LevelLength(int level, int branchingOrder) => Pow2N(branchingOrder, level + 1);
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// These are for when orders of length <= 64 only take up 1 item, e.g. ulong bitmasks.
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static int LevelOffset64(int level, int branchingOrder) => math.min(level, 6/branchingOrder) + LevelOffset(math.max(0, level - 6/branchingOrder), branchingOrder);
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static int LevelLength64(int level, int branchingOrder) => Pow2N(branchingOrder, math.max(0, level - 6/branchingOrder + 1));
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static (int, int) AllocateRange<T>(int length, ref int dataSize) where T : struct
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{
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dataSize = AlignForward(dataSize, UnsafeUtility.AlignOf<T>());
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var range = (dataSize, length);
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dataSize += length * UnsafeUtility.SizeOf<T>();
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return range;
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}
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static int AlignForward(int offset, int alignment)
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{
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var modulo = offset % alignment;
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if (modulo != 0) offset += (alignment - modulo);
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return offset;
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}
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static void* PtrAdd(void* ptr, int bytes) => (void*) ((IntPtr) ptr + bytes);
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static int Pow2(int n) => 1 << n;
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// (2^x)^n = 2^(x*n)
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static int Pow2N(int x, int n) => 1 << (x * n);
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}
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}
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