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    crc-32
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    1.2.0 • Public • Published

    crc32

    Standard CRC-32 algorithm implementation in JS (for the browser and nodejs). Emphasis on correctness, performance, and IE6+ support.

    Installation

    With npm:

    $ npm install crc-32

    In the browser:

    <script src="crc32.js"></script>

    The browser exposes a variable CRC32.

    When installed globally, npm installs a script crc32 that computes the checksum for a specified file or standard input.

    The script will manipulate module.exports if available . This is not always desirable. To prevent the behavior, define DO_NOT_EXPORT_CRC.

    Usage

    In all cases, the relevant function takes an argument representing data and an optional second argument representing the starting "seed" (for rolling CRC).

    The return value is a signed 32-bit integer.

    • CRC32.buf(byte array or buffer[, seed]) assumes the argument is a sequence of 8-bit unsigned integers (nodejs Buffer, Uint8Array or array of bytes).

    • CRC32.bstr(binary string[, seed]) assumes the argument is a binary string where byte i is the low byte of the UCS-2 char: str.charCodeAt(i) & 0xFF

    • CRC32.str(string[, seed]) assumes the argument is a standard JS string and calculates the hash of the UTF-8 encoding.

    For example:

    // var CRC32 = require('crc-32');             // uncomment this line if in node
    CRC32.str("SheetJS")                          // -1647298270
    CRC32.bstr("SheetJS")                         // -1647298270
    CRC32.buf([ 83, 104, 101, 101, 116, 74, 83 ]) // -1647298270
     
    crc32 = CRC32.buf([83, 104])                  // -1826163454  "Sh"
    crc32 = CRC32.str("eet", crc32)               //  1191034598  "Sheet"
    CRC32.bstr("JS", crc32)                       // -1647298270  "SheetJS"
     
    [CRC32.str("\u2603"),  CRC32.str("\u0003")]   // [ -1743909036,  1259060791 ]
    [CRC32.bstr("\u2603"), CRC32.bstr("\u0003")]  // [  1259060791,  1259060791 ]
    [CRC32.buf([0x2603]),  CRC32.buf([0x0003])]   // [  1259060791,  1259060791 ]

    Testing

    make test will run the nodejs-based test.

    To run the in-browser tests, run a local server and go to the ctest directory. make ctestserv will start a python SimpleHTTPServer server on port 8000.

    To update the browser artifacts, run make ctest.

    To generate the bits file, use the crc32 function from python zlib:

    >>> from zlib import crc32
    >>> x="foo bar baz٪☃🍣"
    >>> crc32(x)
    1531648243
    >>> crc32(x+x)
    -218791105
    >>> crc32(x+x+x)
    1834240887

    The included crc32.njs script can process files or standard input:

    echo "this is a test" > t.txt
    $ bin/crc32.njs t.txt
    1912935186

    For comparison, the included crc32.py script uses python zlib:

    $ bin/crc32.py t.txt
    1912935186

    On OSX the command cksum generates unsigned CRC-32 with Algorithm 3:

    $ cksum -o 3 < IE8.Win7.For.Windows.VMware.zip
    1891069052 4161613172
    $ crc32 --unsigned ~/Downloads/IE8.Win7.For.Windows.VMware.zip
    1891069052

    Performance

    make perf will run algorithmic performance tests (which should justify certain decisions in the code).

    The adler-32 project has more performance notes

    License

    Please consult the attached LICENSE file for details. All rights not explicitly granted by the Apache 2.0 license are reserved by the Original Author.

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    Install

    npm i crc-32

    DownloadsWeekly Downloads

    2,418,890

    Version

    1.2.0

    License

    Apache-2.0

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