def test_select_binary_search_bug_is_not_present_2020_09_06() -> None:
i = 3586
bits = bitarray(i)
bits.setall(False)
bits[0] = True
bits[i - 1] = True
poppy = Poppy(bits)
assert poppy.select(0) == 0
assert poppy.select(1) == i - 1
def test_select_poppy_big(byte_value: int, num_bytes: int,
step_size: int) -> None:
bits = bitarray()
bits.frombytes(bytes([byte_value]) * num_bytes)
poppy = Poppy(bits)
a = 0
for i, b in enumerate(bits):
if b:
if i % step_size == 0:
assert poppy.select(a) == i
a += 1
def test_select_poppy(bb: bytes) -> None:
assume(len(bb) % 8 == 0)
bits = bitarray()
bits.frombytes(bb)
poppy = Poppy(bits)
select_answers: List[int] = []
for i in range(len(bits)):
if bits[i]:
select_answers.append(i)
for i, pos in enumerate(select_answers):
assert poppy.select(i) == pos
class LoudsBinaryTree:
def __init__(
self,
*,
root: A,
get_left_child: Callable[[A], Optional[A]],
get_right_child: Callable[[A], Optional[A]]
) -> None:
queue = deque([root])
self._bits = bitarray()
while queue:
tree_node = queue.popleft()
for child in [get_left_child(tree_node), get_right_child(tree_node)]:
if child is not None:
self._bits.append(True)
queue.append(child)
else:
self._bits.append(False)
self._poppy = Poppy(self._bits)
def get_root(self) -> int:
return 0
def get_parent(self, i: int) -> Optional[int]:
if i == 0:
return None
return math.floor(self._poppy.select(i - 1) / 2)
def get_left_child(self, i: int) -> Optional[int]:
if not self._bits[2 * i]:
return None
return self._poppy.rank(2 * i)
def get_right_child(self, i: int) -> Optional[int]:
if not self._bits[2 * i + 1]:
return None
return self._poppy.rank(2 * i + 1)
def is_leaf(self, i: int) -> bool:
return not (self._bits[2 * i] or self._bits[2 * i + 1])
class EliasFano:
def __init__(self, values: Iterator[int], *, num_values: int,
max_value: int) -> None:
"""
Compressed representation of a monotonically-increasing sequence of
nonnegative integers.
"""
# Number of bits needed to store the largest value.
w = math.ceil(math.log2(max(1, max_value)))
# Number of lower-order bits of each value to store in the lower
# bit vector.
num_lower_bits = math.floor(max_value / num_values)
self._num_lower_bits = num_lower_bits
if num_lower_bits != 0:
self._lower_bits = bitarray()
else:
self._lower_bits = None
# Number of higher-order bits of each value to store in the upper bit
# vector.
self._num_upper_bits = w - num_lower_bits
self._upper_bits = bitarray()
previous_value = 0
for value in values:
if value > max_value:
raise ValueError(
f"The value '{value}' is larger than the max_value '{max_value}'"
)
if value < previous_value:
raise ValueError(
"Values must be non-decreasing. "
f"(Found '{previous_value}' followed by '{value}')")
if self._lower_bits is not None:
binary_str = f"{value:b}"
lower_bits_str = binary_str[-num_lower_bits:].rjust(
num_lower_bits, '0')
self._lower_bits.extend(lower_bits_str)
upper_bits = value >> num_lower_bits
previous_upper_bits = previous_value >> num_lower_bits
if previous_value != -1:
self._upper_bits.extend(
[False] * max(0, upper_bits - previous_upper_bits))
self._upper_bits.append(True)
previous_value = value
self._upper_bits.append(False)
self._upper_poppy = Poppy(self._upper_bits)
def __getitem__(self, key: int) -> int:
if self._lower_bits is not None:
lower_offset = key * self._num_lower_bits
lower = int(
self._lower_bits[lower_offset:lower_offset +
self._num_lower_bits].to01(), 2)
else:
lower = 0
upper = self._upper_poppy.select(key) - key
return (upper << self._num_lower_bits) | lower
class Permutation:
def __init__(self, values: IndexedIntSequence) -> None:
runs = self._extract_runs(values)
self._build_huffman_tree(values, runs)
def _extract_runs(self, values: IndexedIntSequence) -> List[HuffmanTreeNode]:
run_starts: List[int] = [0]
for i in range(1, len(values)):
if values[i] < values[i - 1]:
run_starts.append(i)
run_starts_bitarray = bitarray(len(values))
run_starts_bitarray.setall(False)
for start in run_starts:
run_starts_bitarray[start] = True
self._run_starts = Poppy(run_starts_bitarray)
runs: List[HuffmanTreeNode] = []
for i in range(len(run_starts)):
from_index = run_starts[i]
until_index = run_starts[i + 1] if i + 1 < len(run_starts) else len(values)
runs.append(Run(from_=from_index, until=until_index))
return runs
def _build_huffman_tree(self, values: IndexedIntSequence, tree_nodes: List[HuffmanTreeNode]) -> None:
# Determine the tree topology.
heapq.heapify(tree_nodes)
merge_sort_bitarray = bitarray()
merge_sort_offset = 0
while len(tree_nodes) > 1:
x = heapq.heappop(tree_nodes)
y = heapq.heappop(tree_nodes)
merged = HuffmanInnerNode(
size=len(x) + len(y),
left_child=x,
right_child=y,
merge_sort_offset=merge_sort_offset
)
# Populate the merge sort bitarray's values
it_left = ((value, False) for value in x.iterator(values, merge_sort_bitarray))
it_right = ((value, True) for value in y.iterator(values, merge_sort_bitarray))
for _, b in heapq.merge(it_left, it_right):
merge_sort_bitarray.append(b)
merge_sort_offset += 1
heapq.heappush(tree_nodes, merged)
# Build a LOUDS representation of the tree topology
louds = LoudsBinaryTree(
root=tree_nodes[0],
get_left_child=lambda n: n.left_child if isinstance(n, HuffmanInnerNode) else None,
get_right_child=lambda n: n.right_child if isinstance(n, HuffmanInnerNode) else None
)
# The data stored at each node of the tree is:
# - The offset into a bitarray (if a node is an inner node)
# - The offset into the original permutation (if a node is a leaf node)
node_data: List[int] = []
sizes: List[int] = []
queue = deque(tree_nodes)
while queue:
tree_node = queue.popleft()
if isinstance(tree_node, HuffmanInnerNode):
node_data.append(tree_node.merge_sort_offset)
sizes.append(len(tree_node))
queue.append(tree_node.left_child)
queue.append(tree_node.right_child)
elif isinstance(tree_node, Run):
node_data.append(tree_node.from_)
sizes.append(len(tree_node))
else:
raise TypeError
self._louds = louds
self._node_data = node_data
self._merge_sort_poppy = Poppy(merge_sort_bitarray)
number_of_runs = self._run_starts.rank(len(self._run_starts) - 1)
self._run_rank_to_louds_id = [0] * number_of_runs
for louds_id in range(len(self._node_data)):
if self._louds.is_leaf(louds_id):
run_offset = self._node_data[louds_id]
run_rank = self._run_starts.rank(run_offset)
self._run_rank_to_louds_id[run_rank - 1] = louds_id
def __getitem__(self, key: int) -> int:
"""
Retrieve the i'th element of this permutation.
"""
"""
Start at the leaves. Find the index of the current key `k` in the current
node. Now, consider the parent node:
- If the current node is the left child, get the index of the `k`'th
zero in the parent node via "select_zero".
- If the current node is the right child, get the index of the `k`th
one in the parent node via "select".
Repeat until the current node is the root, and return `k`.
"""
run_start = self._run_starts.rank(key) - 1
current_node = self._run_rank_to_louds_id[run_start]
key = key - self._node_data[current_node]
while True:
parent = self._louds.get_parent(current_node)
if parent is None:
return key
else:
parent_offset = self._node_data[parent]
if self._louds.get_left_child(parent) == current_node:
# # get the index of the `k`'th zero in the parent node
parent_rank_zero = (
0 if parent_offset == 0 else
self._merge_sort_poppy.rank_zero(parent_offset - 1)
)
key = self._merge_sort_poppy.select_zero(key + parent_rank_zero) - parent_offset
current_node = parent
else:
# get the index of the `k`th one in the parent node
parent_rank = (
0 if parent_offset == 0 else
self._merge_sort_poppy.rank(parent_offset - 1)
)
key = self._merge_sort_poppy.select(key + parent_rank) - parent_offset
current_node = parent
def index_of(self, value: int) -> int:
"""
Retrieve the index of the given value within this permutation. (This is
the inverse of the permutation.)
"""
"""
Start at the root. Look up the bit at position `value`. Calculate either
the rank_1 or rank_0 of that position, depending on whether it's 1 or 0.
Recurse to either the left or right child, depending on that value.
"""
current_node = self._louds.get_root()
while True:
if self._louds.is_leaf(current_node):
return self._node_data[current_node] + value
else:
offset = self._node_data[current_node]
bit_value = self._merge_sort_poppy[offset + value]
if not bit_value:
value = (
self._merge_sort_poppy.rank_zero(offset + value) -
(
0 if offset == 0 else
self._merge_sort_poppy.rank_zero(offset - 1)
)
) - 1
child = self._louds.get_left_child(current_node)
else:
value = (
self._merge_sort_poppy.rank(offset + value) -
(
0 if offset == 0 else
self._merge_sort_poppy.rank(offset - 1)
)
) - 1
child = self._louds.get_right_child(current_node)
assert child is not None
current_node = child