private static void add(int a, int b, int c) {
        Map<Integer, Integer> entry;
        if (types.containsKey(a)) {
            entry = types.get(a);
        } else {
            entry = new HashMap<Integer, Integer>();
        }
        entry.put(b, c);
        types.put(a, entry);
    }
This class implements a lookup table for result node type conversion.

@author Ulf Lilleengen
searchlib/src/main/java/com/yahoo/searchlib/expression/ArithmeticTypeConversion.java