PHP单个字符大小写转换类

<?php
/*
 *
 * @class Base_Char
 * @author zhangys
 * @date   2012/06/25
 */

class Base_Var_Char
{
    public static function isUpper ( $char )
    {
        $ascii = ord ( $char );
        if( $ascii > 64 and $ascii < 91 ) return true;
        return false;
    }

    public static function isLower ( $char )
    {
        $ascii = ord ( $char );
        if( $ascii > 96 and $ascii < 123 ) return true;
        return false;
    }

    public static function toUpper ( $char )
    {
        if ( self::isUpper ( $char ) ) return $char;
        $ascii = ord ( $char );
        return chr ( $ascii - 32 );
    }

    public static function toLower ( $char )
    {
        if ( self::isLower ( $char ) ) return $char;
        $ascii = ord ( $char );
        return chr ( $ascii + 32 );
    }
}