Design a dynamic array using three values: ptr (pointer to the data), len (number of elements), cap (capacity -- how many elements fit before growing). Pack these into three consecutive i64 values in memory:

fn da_new() i64 {
    var da: i64 = alloc(24);
    store64(da, 0);       // ptr = null
    store64(da + 8, 0);   // len = 0
    store64(da + 16, 0);  // cap = 0
    return da;
}

fn da_len(da: i64) i64 { return load64(da + 8); }

fn da_get(da: i64, i: i64) i64 {
    return load64(load64(da) + i * 8);
}