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"""
Generate a table of unique items.
The `UniqueTable` class collects items into an array, removing duplicates. Each
item is mapped to its offset in the final array.
This is a compression technique for compile-time generated tables.
"""
try:
from typing import Any, List, Dict, Tuple, Sequence # noqa
except ImportError:
pass
class UniqueTable:
"""
Collect items into the `table` list, removing duplicates.
"""
def __init__(self):
# type: () -> None
# List of items added in order.
self.table = list() # type: List[Any]
# Map item -> index.
self.index = dict() # type: Dict[Any, int]
def add(self, item):
# type: (Any) -> int
"""
Add a single item to the table if it isn't already there.
Return the offset into `self.table` of the item.
"""
if item in self.index:
return self.index[item]
idx = len(self.table)
self.index[item] = idx
self.table.append(item)
return idx
class UniqueSeqTable:
"""
Collect sequences into the `table` list, removing duplicates.
Sequences don't have to be of the same length.
"""
def __init__(self):
# type: () -> None
self.table = list() # type: List[Any]
# Map seq -> index.
self.index = dict() # type: Dict[Tuple[Any, ...], int]
def add(self, seq):
# type: (Sequence[Any]) -> int
"""
Add a sequence of items to the table. If the table already contains the
items in `seq` in the same order, use those instead.
Return the offset into `self.table` of the beginning of `seq`.
"""
if len(seq) == 0:
return 0
tseq = tuple(seq)
if tseq in self.index:
return self.index[tseq]
idx = len(self.table)
self.table.extend(tseq)
# Add seq and all sub-sequences to `index`.
index = self.index # type: Dict[Tuple[Any, ...], int]
assert index is not None
for length in range(1, len(tseq) + 1):
for offset in range(len(tseq) - length + 1):
key = tseq[offset:offset+length]
index[key] = idx + offset
return idx
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