persistable sclass BlockOptimizedIntMatrix<A> extends AbstractMatrix<A> {
  // Each block is square with side length being a power of two
  // (i.e. blockSize = 1 << blockBits)
  int blockBits, blockSize;
  
  int bw, bh; // number of block cols/block rows
  
  int[] simpleBlocks;
  int[][] fullBlocks;
  
  *(int *w, int *h, int *blockBits) {
    blockSize = 1 << blockBits;
    bw = rshift_ceil(w, blockSize);
    bh = rshift_ceil(h, blockSize);
  }
  
  public A get(int x, int y) { ret data[y*w+x]; }
  public void set(int x, int y, A a) { data[y*w+x] = a; }
}