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- # Copyright 2024 Google LLC
- #
- # Licensed under the Apache License, Version 2.0 (the "License");
- # you may not use this file except in compliance with the License.
- # You may obtain a copy of the License at
- #
- # http://www.apache.org/licenses/LICENSE-2.0
- #
- # Unless required by applicable law or agreed to in writing, software
- # distributed under the License is distributed on an "AS IS" BASIS,
- # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- # See the License for the specific language governing permissions and
- # limitations under the License.
- CRC_POLY = 0x04C11DB7
- def precompute_table(bits):
- lookup_table = []
- for i in range(2**bits):
- rr = i << (32 - bits)
- for x in range(bits):
- if rr & 0x80000000:
- rr = (rr << 1) ^ CRC_POLY
- else:
- rr <<= 1
- lookup_table.append(rr & 0xffffffff)
- return lookup_table
- lookup_table = precompute_table(8)
- def process_word(data, crc=0xffffffff):
- if (len(data) < 4):
- # The CRC data is "padded" in a very unique and confusing fashion.
- data = data[::-1] + b'\0' * (4 - len(data))
- for char in reversed(data):
- b = char
- crc = ((crc << 8) ^ lookup_table[(crc >> 24) ^ b]) & 0xffffffff
- return crc
- def process_buffer(buf, c=0xffffffff):
- word_count = (len(buf) + 3) // 4
- crc = c
- for i in range(word_count):
- crc = process_word(buf[i * 4 : (i + 1) * 4], crc)
- return crc
- def crc32(data):
- return process_buffer(data)
- if __name__ == '__main__':
- import sys
- assert(0x89f3bab2 == process_buffer("123 567 901 34"))
- assert(0xaff19057 == process_buffer("123456789"))
- assert(0x519b130 == process_buffer("\xfe\xff\xfe\xff"))
- assert(0x495e02ca == process_buffer("\xfe\xff\xfe\xff\x88"))
- print("All tests passed!")
- if len(sys.argv) >= 2:
- b = open(sys.argv[1]).read()
- crc = crc32(b)
- print("%u or 0x%x" % (crc, crc))
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