crc32(3tcl)

💖 crc32 — bestie edition 💖

okay so this is the crc32(3tcl) page from the Cyclic Redundancy Checks family, and it's literally about doing a 32bit Cyclic Redundancy Check. no cap. let's get into it 🦋

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✨ NAME ✨

crc32 — Perform a 32bit Cyclic Redundancy Check. that's it, that's the whole vibe 💅

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🌸 SYNOPSIS 🌸

package require Tcl 8.5 9

package require crc32 ?1.3.4?

::crc::crc32  ?-format format? ?-seed value? [ -channel chan | -filename
file | message ]

::crc::Crc32Init ?seed?

::crc::Crc32Update token data

::crc::Crc32Final token

like yes, it needs Tcl 8.5 or 9, and it wants the crc32 package (?1.3.4? — version optional bestie, no pressure) 💜

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🎀 DESCRIPTION 🎀

so this package gives you a Tcl implementation of the CRC-32 algorithm, based upon information provided at

http://www.naaccr.org/standard/crc32/document.html

and here's the tea: if either the critcl package or the Trf package are available, then a compiled version may be used internally to accelerate the checksum calculation. so it goes zoom when it can 🏎️✨

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👑 COMMANDS 👑

• ::crc::crc32 ?-format format? ?-seed value? [ -channel chan | -filename file | message ] — this one takes either string data or a channel or file name, and returns a checksum value calculated using the CRC-32 algorithm. the result is formatted using the format(3tcl) specifier you hand it. the default? it returns the value as an unsigned integer (format %u). cute, simple, iconic 🌟

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💅 OPTIONS 💅

• -channel name — return a checksum for the data read from a channel. the command will read data from the channel until the eof is true. heads up tho: if you need to be able to process events during this calculation, go look at the PROGRAMMING INTERFACE section instead 👀
• -filename name — this is a convenience option bestie 🫶 it opens the specified file, sets the encoding to binary, and then acts as if the -channel option had been used. the file is closed on completion. so clean, so tidy.
• -format string — return the checksum using an alternative format template. slay ✨
• -seed value — select an alternative seed value for the CRC calculation. the default is 0xffffffff. this can be useful for calculating the CRC for data structures without first converting the whole structure into a string — the CRC of the previous member can be used as the seed for calculating the CRC of the next member. but listen 💀: note that the crc32 algorithm includes a final XOR step. if incremental processing is desired then this must be undone before using the output of the algorithm as the seed for further processing. a simpler alternative is to use the PROGRAMMING INTERFACE, which is intended for this mode of operation. so like, you can do it the hard way, but why 😭

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🌈 PROGRAMMING INTERFACE 🌈

the CRC-32 package implements the checksum using a context variable to which additional data can be added at any time. this is expecially useful in an event based environment such as a Tk application or a web server package 🧚 data to be checksummed may be handled incrementally during a fileevent handler in discrete chunks. this can improve the interactive nature of a GUI application and can help to avoid excessive memory consumption. main character energy fr fr 👑

• ::crc::Crc32Init ?seed? — begins a new CRC32 context. returns a token ID that must be used for the remaining functions. an optional seed may be specified if required. hold onto that token bestie, you need it 💖
• ::crc::Crc32Update token data — add data to the checksum identified by token. calling Crc32Update $token "abcd" is equivalent to calling Crc32Update $token "ab" followed by Crc32Update $token "cb". see EXAMPLES. (yes it says "cb", we don't make the rules, we just report them faithfully 🙈)
• ::crc::Crc32Final token — returns the checksum value and releases any resources held by this token. once this command completes the token will be invalid. the result is a 32 bit integer value. bye token, you served well 🫡

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⭐ EXAMPLES ⭐

look at these, they ate:

% crc::crc32 "Hello, World!"
3964322768

% crc::crc32 -format 0x%X "Hello, World!"
0xEC4AC3D0

% crc::crc32 -file crc32.tcl
483919716

% set tok [crc::Crc32Init]
% crc::Crc32Update $tok "Hello, "
% crc::Crc32Update $tok "World!"
% crc::Crc32Final $tok
3964322768

see how the incremental version lands on the exact same number? that's the whole point bestie, consistency is the aesthetic 💜

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🦋 AUTHORS 🦋

Pat Thoyts

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💀 BUGS, IDEAS, FEEDBACK 💀

ngl, this document and the package it describes will undoubtedly contain bugs and other problems. it's giving... honest 😭 please report such in the category crc of the Tcllib Trackers:

http://core.tcl.tk/tcllib/reportlist

please also report any ideas for enhancements you may have for either the package and/or the documentation. we love ideas here 💖

when proposing code changes, please provide unified diffs, i.e the output of diff -u.

note further that attachments are strongly preferred over inlined patches. attachments can be made by going to the Edit form of the ticket immediately after its creation, and then using the left-most button in the secondary navigation bar. iykyk 🎀

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🔥 SEE ALSO 🔥

cksum(3tcl), crc16(3tcl), sum(3tcl)

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🍓 KEYWORDS 🍓

checksum, cksum, crc, crc32, cyclic redundancy check, data integrity, security

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🧚 CATEGORY 🧚

Hashes, checksums, and encryption

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💜 COPYRIGHT 💜

Copyright (c) 2002, Pat Thoyts

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okay that's the whole page, we did it 💅✨ this came from tcllib, version 1.3.4, dated with the crc32(3tcl) manual page energy — bye bestie, go checksum something 🫶🌸