Compares the argument strings bit wise starting at bit number 0. The returned value is the bit number of the first bit in which the strings differ, or -1 if the strings are identical.

BITCOMP(string1,string2,bit[,pad])

BITCOMP('7F'x,'FF'x) 			 7
BITCOMP('FF'x,'FF'x)     		-1
BITCOMP('FFF'x,'FF'x,'F'x)      	-1
BITCOMP('11000011'b, '11010011'b,)       4