The easiest wat to do it is with a ROM. That's a Read Only Memory. You take the first sixteen locations and write the pattern of 1's and 0's that corresponds to the input on the address lines. Tie the other address lines low and tie the chip select low.
Next easiest method is to write the boolean equations for each segment as a sum of products. There will be one product term with four factors for each input combination that lights a segment. Then program a PAL or a small gate arry with those equations.
Another way to do it is to program a PIC to look at the four inputs and output the appropriate value.
Another way to do it is ...well I guess three is enough to keep you off the streets.