ISIGNED converts the expression x into a signed FIXED BINARY value without changing the bit pattern. If x is signed, the precision of the returned value is the same as that of x. If it is unsigned, the precision of the returned value is the same as that of x unless the precision of x is 8, 16, 32 or 64. In that case the precision of the returned signed FIXED BINARY is equal to that of x minus 1.