x86 assembly language ---must use at least 1 function (in addition to _main or _start) and 2 string instructions

The count of the number of unique (count each letter once) letters. Example: The man ran. has 7 unique letters. Provide the count of unique letters in each string, and for over the 2 strings together. Additional programming requirements: Your results should be stored in variables (though you may use registers for intermediary steps). Your program must use at least 2 string instructions. You may use jump instructions and possibly loop instructions if needed. You are required to use at least one function (in addition to _main or _start) where you pass in at least one variable. Your additional function is required to use registers in its operations.