private char Normalize(char ch)
{
if (ch.IsUpperCase())
{
//convert a upper letter to lower.
ch = (char)((int)ch + 32);
}
else if (ch >= 0xff01 && ch <= 0xff5d)
{
//convert a fullwidth char to halfwidth.
ch = (char)((int)ch - 0xFEE0);
}
return ch;
}