尝试将此 C# 数学移植到 PHP:int 掩码 = 1 << (i - 1）;

我正在尝试将这个C#数学（我猜？）移植到PHP：int mask = 1 << (i - 1);下面是该函数的完整 C# 代码：

/// <summary>
/// Converts tile XY coordinates into a QuadKey at a specified level of detail.
/// </summary>
/// <param name="tileX">Tile X coordinate.</param>
/// <param name="tileY">Tile Y coordinate.</param>
/// <param name="levelOfDetail">Level of detail, from 1 (lowest detail)
/// to 23 (highest detail).</param>
/// <returns>A string containing the QuadKey.</returns>
public static string TileXYToQuadKey(int tileX, int tileY, int levelOfDetail)
{
    StringBuilder quadKey = new StringBuilder();
    for (int i = levelOfDetail; i > 0; i--)
    {
        char digit = '0';
        int mask = 1 << (i - 1);
        if ((tileX & mask) != 0)
        {
            digit++;
        }
        if ((tileY & mask) != 0)
        {
            digit++;
            digit++;
        }
        quadKey.Append(digit);
    }
    return quadKey.ToString();
}

这是我最终得到的PHP代码：

<?php
/*
* PHP class for converting Mercator X, Y and Z
* coordinates to Bing Maps Quad tree key
* Ported from C# code from MSDN
* http://msdn.microsoft.com/en-us/library/bb259689.aspx
*
* Usage:
* mercatorQuadkey(z, x, y)
* Example:
* mercatorQuadkey(15, 5240, 12661)
*/
function mercatorQuadkey($z, $x, $y){
    for ($i = $levelOfDetail; $i > 0; $i--)
    {
        $digit = '0';
        $mask = 1 << ($i - 1);
        if ($tileX !== 0 && $mask !== 0)
        {
            $digit++;
        }
        if ($tileY !== 0 && $mask !== 0)
        {
            $digit++;
            $digit++;
        }
        $quadkey = $quadkey.$digit;
    }
    return $quadkey;
}
?>

谁能帮忙？我需要这个，因为我正在尝试在传单中使用 Bing 地图，但我找到的所有插件都没有使用示例。顺便说一下，我对 C# 一无所知。