forked from Imagelibrary/littlefs
33e2e5b1db
This is actually faster than a byte-wise xor in Python: parity.py disk (1MiB) w/ crc32c lib: 0m0.027s parity.py disk (1MiB) w/o crc32c lib: 0m0.051s There's probably some other library that can do this even faster, but parity.py is not a critical script.
104 lines
2.7 KiB
Python
Executable File
104 lines
2.7 KiB
Python
Executable File
#!/usr/bin/env python3
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# prevent local imports
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if __name__ == "__main__":
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__import__('sys').path.pop(0)
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import io
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import os
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import struct
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import sys
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import functools as ft
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import operator as op
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try:
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import crc32c as crc32c_lib
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except ModuleNotFoundError:
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crc32c_lib = None
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def openio(path, mode='r', buffering=-1):
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# allow '-' for stdin/stdout
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import os
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if path == '-':
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if 'r' in mode:
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return os.fdopen(os.dup(sys.stdin.fileno()), mode, buffering)
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else:
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return os.fdopen(os.dup(sys.stdout.fileno()), mode, buffering)
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else:
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return open(path, mode, buffering)
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def crc32c(data, crc=0):
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if crc32c_lib is not None:
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return crc32c_lib.crc32c(data, crc)
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else:
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crc ^= 0xffffffff
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for b in data:
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crc ^= b
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for j in range(8):
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crc = (crc >> 1) ^ ((crc & 1) * 0x82f63b78)
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return 0xffffffff ^ crc
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def popc(x):
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return bin(x).count('1')
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def parity(x):
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return popc(x) & 1
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def main(paths, **args):
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# interpret as sequence of hex bytes
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if args.get('hex'):
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bytes_ = [b for path in paths for b in path.split()]
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print('%01x' % parity(crc32c(bytes(int(b, 16) for b in bytes_))))
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# interpret as strings
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elif args.get('string'):
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for path in paths:
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print('%01x' % parity(crc32c(path.encode('utf8'))))
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# default to interpreting as paths
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else:
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if not paths:
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paths = [None]
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for path in paths:
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with openio(path or '-', 'rb') as f:
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# calculate crc, crc32c preserves parity
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crc = 0
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while True:
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block = f.read(io.DEFAULT_BUFFER_SIZE)
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if not block:
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break
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crc = crc32c(block, crc)
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# print what we found
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if path is not None:
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print('%01x %s' % (parity(crc), path))
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else:
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print('%01x' % parity(crc))
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if __name__ == "__main__":
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import argparse
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import sys
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parser = argparse.ArgumentParser(
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description="Calculates parity.",
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allow_abbrev=False)
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parser.add_argument(
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'paths',
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nargs='*',
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help="Paths to read. Reads stdin by default.")
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parser.add_argument(
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'-x', '--hex',
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action='store_true',
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help="Interpret as a sequence of hex bytes.")
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parser.add_argument(
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'-s', '--string',
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action='store_true',
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help="Interpret as strings.")
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sys.exit(main(**{k: v
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for k, v in vars(parser.parse_intermixed_args()).items()
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if v is not None}))
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