com.unity.demoteam.digital-human/Runtime/MeshTools/UnsafeBFS.cs

using System;
using Unity.Collections;

public unsafe struct UnsafeBFS : IDisposable
{
    public int position;
    public int depth;

    private UnsafeArrayULong pending;// pending[i] == (depth << 32) | position
    private int pendingHead;
    private int pendingTail;

    private UnsafeArrayBool visited;

    public UnsafeBFS(int nodeCount, Allocator allocator = Allocator.Temp)
    {
        this.position = -1;
        this.depth = -1;

        this.pending = new UnsafeArrayULong(nodeCount, allocator);
        this.pendingHead = 0;
        this.pendingTail = 0;

        this.visited = new UnsafeArrayBool(nodeCount, allocator);
        this.visited.Clear(false);
    }

    public void Dispose()
    {
        pending.Dispose();
        visited.Dispose();
    }

    public void Clear()
    {
        visited.Clear(false);
    }

    public void Ignore(int node)
    {
        visited.val[node] = true;
    }

    public void Insert(int node)
    {
        if (visited.val[node])
            return;

        ulong pack_position = (ulong)node;
        ulong pack_depth = (ulong)(depth + 1) << 32;

        pending.val[pendingTail++] = pack_depth | pack_position;
        visited.val[node] = true;
    }

    public bool MoveNext()
    {
        if (pendingHead != pendingTail)
        {
            ulong packed = pending.val[pendingHead++];
            position = (int)(packed & 0xffffffffuL);
            depth = (int)(packed >> 32);
            return true;
        }
        else
        {
            position = -1;
            depth = -1;
            return false;
        }
    }
}