急急！请问如何将这个javascript代码改成C#，谢谢
这是一段javascript代码，请问如何把它改成C#，谢谢
function decode56(str){
  var c1, c2, c3, c4,c5=[-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63,52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1, -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1],c6 = str.charCodeAt(0),c7,i, len, out;
  if(!this['][']){
  this[']['] = 1;
  c7=this.decode56(str);
  str = c7.substr(c6); 
  }; 
  len = str.length; 
  i = 1; 
  out = ""; 
  while(i < len) { 
  do { 
  c1 = c5[str.charCodeAt(i++) & 0xff]; 
  } while(i < len && c1 == -1); 
  if(c1 == -1) break; 
  do {
  c2 = c5[str.charCodeAt(i++) & 0xff]; 
  } while(i < len && c2 == -1); 
  if(c2 == -1) break; 
  out += String.fromCharCode((c1 << 2) | ((c2 & 0x30) >> 4)); 
  do { 
  c3 = str.charCodeAt(i++) & 0xff; 
  if(c3 == 61) return out; 
  c3 = c5[c3]; 
  } while(i < len && c3 == -1); 
  if(c3 == -1) break; 
  out += String.fromCharCode(((c2 & 0XF) << 4) | ((c3 & 0x3C) >> 2)); 
  do { 
  c4 = str.charCodeAt(i++) & 0xff;
  if(c4 == 61) return out; 
  c4 = c5[c4]; 
  } while(i < len && c4 == -1); 
  if(c4 == -1) break; 
  out += String.fromCharCode(((c3 & 0x03) << 6) | c4); 
  } 
  return out;
}

------解决方案--------------------
没有测试过，随手改写不能保证其正确率

C# code

private string decode56(string str)
{
    int[] c5 = new int[] { 
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 
        -1, 62, -1, -1, -1, 63, 52, 53, 54, 55, 56, 57, 58, 59,
        60, 61, -1, -1, -1, -1, -1, -1, -1, 0, 1, 2, 3, 4, 5, 6, 
        7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 
        22, 23, 24, 25, -1, -1, -1, -1, -1, -1, 26, 27, 28, 29, 
        30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 
        45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1 };
    char c6 = str[0];
    int len = str.Length; 
    int i = 1;
    string _out = string.Empty;
    int c1, c2, c3, c4;
    while (i < len)
    {
        do
        {
            c1 = c5[str[i++] & 0xff];
        } while (i < len && c1 == -1);
        if (c1 == -1) break;
        do
        {
            c2 = c5[str[i++] & 0xff];
        } while (i < len && c2 == -1);
        if (c2 == -1) break;
        _out += (char)((c1 << 2) | ((c2 & 0x30) >> 4));
        do
        {
            c3 = str[i++] & 0xff;
            if (c3 == 61) return _out;
            c3 = c5[c3];
        }
        while (i < len && c3 == -1);
        if (c3 == -1) break;
        _out += (char)((((c2 & 0XF) << 4) | ((c3 & 0x3C) >> 2)));
        do