general pattern for implementing truth tables
c++
Solution
int condition = ( prev >= 0 ? ( 1<<0 ) : 0 ) +
( cur >= 0 ? ( 1<<1 ) : 0 ) +
( next >= 0 ? ( 1<<2 ) : 0 );
switch (condition) {
case 0: // - - -
case 1: // + - -
case 2: // - + -
case 3: // + + -
case 4: // - - +
case 5: // + - +
case 6: // - + +
case 7: // + + +
}
Problem
Is there a good general pattern for implementing truth tables? I am re-working some legacy code (C++) and just realized that the function I am working with amounts to a truth table with 3 binary inputs and 8 possible outputs. Here is an example of two of the eight tests and corresponding outputs: ``` // - + + if ( (prevdst5 < 0.0) && (dst5 > 0.0) && (nextdst5 > 0.0) ){ thawpct = (dst5 / (dst5 - prevdst5)); } // - - + if ( (prevdst5 < 0.0) && (dst5 < 0.0) && (nextdst5 > 0.0) ){ thawpct = (nextdst5 / (nextdst5 - dst5)); } // other cases... return thawpct; ``` Basically I am wondering if there is a cleaner, more maintainable/extensible* way to set this up. - What if another input is added? Then the number of if statements needed would be 16, which in my view, would be too cumbersome to manage with the current pattern. - What if several of the input combos should map to the same output? *The codebase is an ecosystem model used in academia, so maintenance and extension amount to similar things depending on the perspective of the coder.