days y m = 28 + (m + (m `div` 8)) `mod` 2 + 2 `mod` m + 2 * (1 `div` m) 
               + ((2 `div` m) `mod` 2) * (leap y)
      where leap y = multiple 4 y - multiple 100 y + multiple 400 y
              where multiple int y = ((y + (int - 1)) `mod` int + 1) `div` int

    function f(x) { return 28 + maybeLeap(x) + (...); }

        leap = function(x) { 
          if ((x % 4) != 0) {
            return 0;
          }
          return Number(
            (x % 100) != 0 || (x % 400) == 0
          );
        }

        function(x) { return 28 + leap(x) + (...) };