stgsharp/StgSharp.Common/HighPerformance/Memory/old/HLSFAllocator.Level.cs

//-----------------------------------------------------------------------
// -----------------------------------------------------------------------
// file="HLSFAllocator.Level"
// Project: StgSharp
// AuthorGroup: Nitload
// Copyright (c) Nitload. All rights reserved.
//     
// Permission is hereby granted, free of charge, to any person obtaining a copy
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using System;
using System.Collections.Generic;
using System.Linq;
using System.Net.Security;
using System.Numerics;
using System.Runtime.CompilerServices;
using System.Text;
using System.Threading.Tasks;

namespace StgSharp.HighPerformance.Memory
{
    public unsafe partial class HybridLayerSegregatedFitAllocator
    {

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private nuint GetAllocSize(
                      nuint size
        )

        {
            return (size + 63u) & (~63u);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private int GetBucketIndexOnce(
                    nuint size
        )
        {
            int log2Size = 63 - BitOperations.LeadingZeroCount((ulong)size);

            // Calculate level: level = max(0, (log2Size - 6) / 2)
            int level = Math.Max(0, (log2Size - 6) / 2);

            // caller is responsible for ensuring level is within bounds
            level = Math.Min(level, _maxLevel);
            uint levelSize = 1u << (log2Size & (~1));
            int segment = ((int)(size / levelSize)) - 1;
            return Math.Min((level * 3) + segment, _bucketHeads.Length - 1);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private (int level, int segment) GetIndexPairOnce(
                                         nuint size
        )
        {
            int log2Size = 63 - BitOperations.LeadingZeroCount((ulong)size);

            // Calculate level: level = max(0, (log2Size - 6) / 2)
            int level = Math.Max(0, (log2Size - 6) / 2);

            // caller is responsible for ensuring level is within bounds
            level = Math.Min(level, _maxLevel);
            uint levelSize = 1u << (log2Size & (~1));
            int segment = ((int)(size / levelSize)) - 1;
            return (level, segment);
        }

        /// <summary>
        ///   NOTICE: returned level may exceed maxLevel, caller is responsible for ensuring the
        ///   returned level is within bounds. This method is designed for performance and does not
        ///   perform bounds checking.
        /// </summary>
        /// <param name="size">
        ///   Size of the memory block to determine level for. This method does not assume size is
        ///   already aligned
        /// </param>
        /// <returns>
        ///   Level corresponding to the given size. Level is determined based on the formula: level
        ///   >= (log2(S) - 6) / 2
        /// </returns>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private int GetLevelFromSize(
                    nuint size
        )
        {
            /*
            * Level sizes: [64, 256, 1024, 4096, 16384, 65536, 262144, 1048576, 4194304, 16777216, ......]
            * Pattern: 64 * 4^level = 2^6 * 2^(2*level) = 2^(6+2*level)
            * 
            * For size S, we need: 2^(6+2*level) >= S
            * So: 6+2*level >= log2(S)
            * Therefore: level >= (log2(S) - 6) / 2
            * 
            * We use hardware LZCNT instruction via BitOperations.LeadingZeroCount
            * log2(S) = 63 - LeadingZeroCount(S) for 64-bit values
            */
            int log2Size = 63 - BitOperations.LeadingZeroCount((ulong)size);

            // Calculate level: level = max(0, (log2Size - 6) / 2)
            int level = Math.Max(0, (log2Size - 6) / 2);

            // caller is responsible for ensuring level is within bounds
            return level;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static uint GetLevelSizeFromLevel(
                            int level
        )
        {
            return 1u << (6 + (2 * level));
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static uint GetLevelSizeFromSize(
                            nuint size
        )
        {
            int log2Size = 63 - BitOperations.LeadingZeroCount((ulong)size);
            return 1u << (log2Size & (~1));
        }

        /// <summary>
        ///   Determine segment index based on size and originLevel. Input level value is regarded
        ///   safe.
        /// </summary>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private int GetSegmentFromLevel(
                    ulong size,
                    int level
        )
        {
            return ((int)(size / GetLevelSizeFromLevel(level))) - 1;
        }

    }
}