81 lines
2.6 KiB
Python
81 lines
2.6 KiB
Python
import math
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import os
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from logging import exception
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from typing import Optional
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class Int2IntMapLike():
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"""
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A file used to map byte numbers of the filter view to byte numbers in the original file.
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Each line contains the two integers separated by a comma.
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The first column is sorted ascending. This allows us to do binary searches.
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The file uses 4kb blocks. That means we add fill bytes (newlines) if a line would cross a 4kb block boundary.
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"""
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blocksize = 4096
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def __init__(self, file):
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self._file = file
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self._handle = open(file, "w+t")
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self._buffer = ""
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def close(self):
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if not self._handle.closed:
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self._handle.close()
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def reset(self):
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self._handle.truncate(0)
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def add(self, start: int, length: int, val: int):
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line = "%d,%d,%d\n" % (start, length, val)
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length = len(line)
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offset = self._handle.tell() + len(self._buffer)
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if offset % self.blocksize + length > self.blocksize:
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# end of block: fill block
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fill_bytes = self.blocksize - offset % self.blocksize
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self._buffer = self._buffer + ("\n" * fill_bytes)
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else:
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self._buffer = self._buffer + line
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def _flush_buffer(self):
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self._handle.write(self._buffer)
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self._buffer = ""
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self._handle.flush()
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def find(self, key: int) -> Optional[int]:
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if (len(self._buffer)) > 0:
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self._flush_buffer()
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size = os.stat(self._file).st_size
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if size == 0:
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return None
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total_blocks = math.ceil(size / self.blocksize)
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step = math.ceil(total_blocks / 2)
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offset = (step - 1) * self.blocksize
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while step >= 1:
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self._handle.seek(offset)
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block = self._handle.read(self.blocksize)
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lines = block.split("\n")
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is_before = None
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for line in lines:
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if len(line) == 0:
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continue
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token = line.split(",")
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start = int(token[0])
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length = int(token[1])
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val = int(token[2])
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if key >= start and key - start < length:
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return val
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tmp = key < start
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if is_before != None and tmp != is_before:
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return None
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is_before = tmp
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if step == 1:
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return None
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step = math.ceil(step / 2)
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if is_before:
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offset = offset - step * self.blocksize
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else:
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offset = offset + step * self.blocksize
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