def summarize_bitmap(bitmap: list) -> str:
    """Give a compact text summary for sparse bitmaps"""
    nonzero_bits = []
    for i, b in enumerate(bitmap):
        if b != 0:
            nonzero_bits.append(f'{i:x}:{b:02x}')
    sorted_nonzero_bits = ', '.join(sorted(nonzero_bits))
    summary = f'{len(nonzero_bits)}/{len(bitmap)}: {sorted_nonzero_bits}'
    return summary