Source code for google.appengine.api.files.crc32c

#!/usr/bin/env python
# Copyright 2007 Google Inc.
# 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
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# See the License for the specific language governing permissions and
# limitations under the License.

"""Implementation of CRC-32C checksumming as in rfc3720 section B.4.

See for details on CRC-32C.

This code is a manual python translation of c code generated by
pycrc 0.7.1 ( Command line used:
'./ --model=crc-32c --generate c --algorithm=table-driven'

import array

    0x00000000L, 0xf26b8303L, 0xe13b70f7L, 0x1350f3f4L,
    0xc79a971fL, 0x35f1141cL, 0x26a1e7e8L, 0xd4ca64ebL,
    0x8ad958cfL, 0x78b2dbccL, 0x6be22838L, 0x9989ab3bL,
    0x4d43cfd0L, 0xbf284cd3L, 0xac78bf27L, 0x5e133c24L,
    0x105ec76fL, 0xe235446cL, 0xf165b798L, 0x030e349bL,
    0xd7c45070L, 0x25afd373L, 0x36ff2087L, 0xc494a384L,
    0x9a879fa0L, 0x68ec1ca3L, 0x7bbcef57L, 0x89d76c54L,
    0x5d1d08bfL, 0xaf768bbcL, 0xbc267848L, 0x4e4dfb4bL,
    0x20bd8edeL, 0xd2d60dddL, 0xc186fe29L, 0x33ed7d2aL,
    0xe72719c1L, 0x154c9ac2L, 0x061c6936L, 0xf477ea35L,
    0xaa64d611L, 0x580f5512L, 0x4b5fa6e6L, 0xb93425e5L,
    0x6dfe410eL, 0x9f95c20dL, 0x8cc531f9L, 0x7eaeb2faL,
    0x30e349b1L, 0xc288cab2L, 0xd1d83946L, 0x23b3ba45L,
    0xf779deaeL, 0x05125dadL, 0x1642ae59L, 0xe4292d5aL,
    0xba3a117eL, 0x4851927dL, 0x5b016189L, 0xa96ae28aL,
    0x7da08661L, 0x8fcb0562L, 0x9c9bf696L, 0x6ef07595L,
    0x417b1dbcL, 0xb3109ebfL, 0xa0406d4bL, 0x522bee48L,
    0x86e18aa3L, 0x748a09a0L, 0x67dafa54L, 0x95b17957L,
    0xcba24573L, 0x39c9c670L, 0x2a993584L, 0xd8f2b687L,
    0x0c38d26cL, 0xfe53516fL, 0xed03a29bL, 0x1f682198L,
    0x5125dad3L, 0xa34e59d0L, 0xb01eaa24L, 0x42752927L,
    0x96bf4dccL, 0x64d4cecfL, 0x77843d3bL, 0x85efbe38L,
    0xdbfc821cL, 0x2997011fL, 0x3ac7f2ebL, 0xc8ac71e8L,
    0x1c661503L, 0xee0d9600L, 0xfd5d65f4L, 0x0f36e6f7L,
    0x61c69362L, 0x93ad1061L, 0x80fde395L, 0x72966096L,
    0xa65c047dL, 0x5437877eL, 0x4767748aL, 0xb50cf789L,
    0xeb1fcbadL, 0x197448aeL, 0x0a24bb5aL, 0xf84f3859L,
    0x2c855cb2L, 0xdeeedfb1L, 0xcdbe2c45L, 0x3fd5af46L,
    0x7198540dL, 0x83f3d70eL, 0x90a324faL, 0x62c8a7f9L,
    0xb602c312L, 0x44694011L, 0x5739b3e5L, 0xa55230e6L,
    0xfb410cc2L, 0x092a8fc1L, 0x1a7a7c35L, 0xe811ff36L,
    0x3cdb9bddL, 0xceb018deL, 0xdde0eb2aL, 0x2f8b6829L,
    0x82f63b78L, 0x709db87bL, 0x63cd4b8fL, 0x91a6c88cL,
    0x456cac67L, 0xb7072f64L, 0xa457dc90L, 0x563c5f93L,
    0x082f63b7L, 0xfa44e0b4L, 0xe9141340L, 0x1b7f9043L,
    0xcfb5f4a8L, 0x3dde77abL, 0x2e8e845fL, 0xdce5075cL,
    0x92a8fc17L, 0x60c37f14L, 0x73938ce0L, 0x81f80fe3L,
    0x55326b08L, 0xa759e80bL, 0xb4091bffL, 0x466298fcL,
    0x1871a4d8L, 0xea1a27dbL, 0xf94ad42fL, 0x0b21572cL,
    0xdfeb33c7L, 0x2d80b0c4L, 0x3ed04330L, 0xccbbc033L,
    0xa24bb5a6L, 0x502036a5L, 0x4370c551L, 0xb11b4652L,
    0x65d122b9L, 0x97baa1baL, 0x84ea524eL, 0x7681d14dL,
    0x2892ed69L, 0xdaf96e6aL, 0xc9a99d9eL, 0x3bc21e9dL,
    0xef087a76L, 0x1d63f975L, 0x0e330a81L, 0xfc588982L,
    0xb21572c9L, 0x407ef1caL, 0x532e023eL, 0xa145813dL,
    0x758fe5d6L, 0x87e466d5L, 0x94b49521L, 0x66df1622L,
    0x38cc2a06L, 0xcaa7a905L, 0xd9f75af1L, 0x2b9cd9f2L,
    0xff56bd19L, 0x0d3d3e1aL, 0x1e6dcdeeL, 0xec064eedL,
    0xc38d26c4L, 0x31e6a5c7L, 0x22b65633L, 0xd0ddd530L,
    0x0417b1dbL, 0xf67c32d8L, 0xe52cc12cL, 0x1747422fL,
    0x49547e0bL, 0xbb3ffd08L, 0xa86f0efcL, 0x5a048dffL,
    0x8ecee914L, 0x7ca56a17L, 0x6ff599e3L, 0x9d9e1ae0L,
    0xd3d3e1abL, 0x21b862a8L, 0x32e8915cL, 0xc083125fL,
    0x144976b4L, 0xe622f5b7L, 0xf5720643L, 0x07198540L,
    0x590ab964L, 0xab613a67L, 0xb831c993L, 0x4a5a4a90L,
    0x9e902e7bL, 0x6cfbad78L, 0x7fab5e8cL, 0x8dc0dd8fL,
    0xe330a81aL, 0x115b2b19L, 0x020bd8edL, 0xf0605beeL,
    0x24aa3f05L, 0xd6c1bc06L, 0xc5914ff2L, 0x37faccf1L,
    0x69e9f0d5L, 0x9b8273d6L, 0x88d28022L, 0x7ab90321L,
    0xae7367caL, 0x5c18e4c9L, 0x4f48173dL, 0xbd23943eL,
    0xf36e6f75L, 0x0105ec76L, 0x12551f82L, 0xe03e9c81L,
    0x34f4f86aL, 0xc69f7b69L, 0xd5cf889dL, 0x27a40b9eL,
    0x79b737baL, 0x8bdcb4b9L, 0x988c474dL, 0x6ae7c44eL,
    0xbe2da0a5L, 0x4c4623a6L, 0x5f16d052L, 0xad7d5351L,



[docs]def crc_update(crc, data): """Update CRC-32C checksum with data. Args: crc: 32-bit checksum to update as long. data: byte array, string or iterable over bytes. Returns: 32-bit updated CRC-32C as long. """ if type(data) != array.array or data.itemsize != 1: buf = array.array("B", data) else: buf = data crc = crc ^ _MASK for b in buf: table_index = (crc ^ b) & 0xff crc = (CRC_TABLE[table_index] ^ (crc >> 8)) & _MASK return crc ^ _MASK
[docs]def crc_finalize(crc): """Finalize CRC-32C checksum. This function should be called as last step of crc calculation. Args: crc: 32-bit checksum as long. Returns: finalized 32-bit checksum as long """ return crc & _MASK
[docs]def crc(data): """Compute CRC-32C checksum of the data. Args: data: byte array, string or iterable over bytes. Returns: 32-bit CRC-32C checksum of data as long. """ return crc_finalize(crc_update(CRC_INIT, data))

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