十六进制转换成十进制SQL函数代码

CREATE   FUNCTION   dbo.f_hex(@str   varchar(16)) 
RETURNS   bigint 
AS 
BEGIN 
    DECLARE   @i   int,@res   bigint 
    SELECT   @i=0,@result=0,@str=RTRIM(LTRIM(UPPER(REVERSE(@str)))) --去除参数的首尾空格
    WHILE   @i <LEN(@str) --遍历参数的每一个字符
    BEGIN 

---限定参数字符的不能超出十六进制的表现形式
        IF   SUBSTRING(@str,@i+1,1)   not   between   '0 '   and   '9 '   and   SUBSTRING(@str,@i+1,1)   not   between   'A '   and   'F ' 
        BEGIN 
            SELECT   @res=0 
            break 
        END 
        SELECT   @res=@res+(CHARINDEX(SUBSTRING(@str,@i+1,1), '0123456789ABCDEF ')-1)*POWER(16,@i),@i=@i+1 
    END 
    RETURN   @res 
END