Function page_commit

scripts/page_commit_reference.py:172–217

(page: bytes)

def page_commit(page: bytes) -> bytes:
    assert len(page) == PAGE_SIZE

    slot_bitmap = compute_slot_bitmap(page)
    if slot_bitmap == 0:
        return hash_seal(0, None)

    pair_bitmap = derive_pair_bitmap(slot_bitmap)

    # Phase 1: hash each active pair-leaf.
    scratch: dict[int, bytes] = {}
    bits = pair_bitmap
    while bits:
        idx = (bits & -bits).bit_length() - 1
        scratch[idx] = hash_leaf(page[idx * 64:(idx + 1) * 64])
        bits &= bits - 1

    # Phase 2: bitmap-driven bottom-up merge.
    bm = pair_bitmap
    for bit in range(6):
        if bin(bm).count("1") <= 1:
            break
        merges: list[tuple[int, int]] = []
        bits = bm
        prev = -1
        while bits:
            pos = (bits & -bits).bit_length() - 1
            bits &= bits - 1
            sibling = (
                prev != -1
                and (prev >> (bit + 1)) == (pos >> (bit + 1))
                and ((prev >> bit) & 1) == 0
            )
            if sibling:
                merges.append((prev, pos))
                prev = -1
            else:
                prev = pos
        for left, right in merges:
            scratch[left] = hash_parent(scratch[left], scratch[right])
            del scratch[right]
            bm &= ~(1 << right)

    # Phase 3: seal.
    root_idx = (bm & -bm).bit_length() - 1
    return hash_seal(slot_bitmap, scratch[root_idx])


# ── Reference vectors (must match the C++ implementation) ───────────────────