say you have a look-up table such as below


00000000 0000100011000010
00000001 0000100000000010
00010000 0000100000011010
00110101 0011000000000001
00101011 0000001100000000

where the entry on the left is the address entry on the right is the returned value,table can be any size you wish.You treat it simply as a truth table for a multi-output boolean function.Any boolean function can be implemented using 'and''or' 'not'.
so the above example can be generated by
v8.0 = ;

v8.1 = ;

v8.2 = (!v0&!v1&v2&v3&!v4&v5&!v6&v7);

v8.3 = (!v0&!v1&v2&v3&!v4&v5&!v6&v7);

v8.4 = (!v0&!v1&!v2&v3&!v4&!v5&!v6&!v7) | (!v0&!v1&!v2&!v3&!v4&!v5&!v6);

v8.5 = ;

v8.6 = (!v0&!v1&v2&!v3&v4&!v5&v6&v7);

v8.7 = (!v0&!v1&v2&!v3&v4&!v5&v6&v7);

v8.8 = (!v0&!v1&!v2&!v3&!v4&!v5&!v6&!v7);

v8.9 = (!v0&!v1&!v2&!v3&!v4&!v5&!v6&!v7);

v8.10 = ;

v8.11 = (!v0&!v1&!v2&v3&!v4&!v5&!v6&!v7);

v8.12 = (!v0&!v1&!v2&v3&!v4&!v5&!v6&!v7);

v8.13 = ;

v8.14 = (!v0&!v1&!v2&v3&!v4&!v5&!v6&!v7) | (!v0&!v1&!v2&!v3&!v4&!v5&!v6);

v8.15 = (!v0&!v1&v2&v3&!v4&v5&!v6&v7);

so the function calculates the boolean function for each of the output bits,the time depends on the number of products in each boolean function.
Finding the minimum boolean function for the output bits is a very tedious task especially when the truth table is large,which is where espresso comes in,its a tool which performs minimization of multivalued boolean functions and is available for download here.
http://www.dei.isep.ipp.pt/~acc/bfunc/
its not the friendliest of peices of software,but command lists can be found with google.wether your LUT minimizes well depends on the type of function,the time taken to minimize a boolean function goes as order(n*n) where n is the number of inputs
the above example was done by 'espresso -o eqntott -Dopo -S1 foo