Memory vs Compute

struct Elem {
  int input;
  int cached_result; // precomputed
};
std::vector<Elem> arr(10'000'000);

for (auto &e : arr) {
  sum += e.cached_result;
}

const FooWithCache = struct {
    values: [30]i32,
    cached_bar: i32 = 0,

    fn bar(self: *FooWithCache) i32 {
        if (self.cached_bar == 0) {
            for (self.values, 0..) |v, i| {
                self.cached_bar +%= v *% @intCast(i);
            }
        }
        return self.cached_bar;
    }
};

var arr: []FooWithCache = // 1'000'000 elems

for (arr) |*foo| use(foo.bar());

struct Elem {
  int input;
};
std::vector<Elem> arr(10'000'000);

for (auto &e : arr) {
  int x = e.input;
  x = x * 7 + 13;
  x = x ^ (x >> 3);
  x = x * 31 + 7;
  x = x ^ (x >> 5);
  x = x * 127 + 63;
  x = x ^ (x >> 7);
  x = x * 17 + 5;
  sum += x;
}

const FooWithoutCache = struct {
    values: [30]i32,

    fn bar(self: *const FooWithoutCache) i32 {
        var res: i32 = 0;
        for (self.values, 0..) |v, i| {
            res +%= v *% @intCast(i);
        }
        return res;
    }
};

var arr: []FooWithoutCache = // 1'000'000 elems

for (arr) |*foo| use(foo.bar());