crc32(n)

💖 crc32(n) — Cyclic Redundancy Checks 💖

okay bestie, sit down, hydrate, because we're about to talk about cyclic redundancy checks and honestly? it's giving iconic. this is the crc32 page from the Tcl manual, section n, and it's about doing a 32bit cyclic redundancy check. yes it's a checksum thing. yes it's important. no you cannot skip it. 🎀

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✨ NAME ✨

crc32 — Perform a 32bit Cyclic Redundancy Check 💅

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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 look at her. so much range. 🦋

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🫶 DESCRIPTION 🫶

so this package gives you a Tcl implementation of the CRC-32 algorithm, and it's based upon the info provided at http://www.naaccr.org/standard/crc32/document.html — yes, that's a whole link, i'm not paraphrasing it, it's literally in the original and i'm not about to lose details on main. 💀

and here's the lowkey 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 she might be running faster than she looks. no cap. 🔥

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👑 COMMANDS 👑

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

okay so this command takes either string data or a channel or file name and returns a checksum value calculated using the CRC-32 algorithm. and then the result gets formatted using the format(n) specifier you provided. the default? it returns the value as an unsigned integer (format %u). periodt. ✨

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💅 OPTIONS 💅

• -channel name — returns a checksum for the data read from a channel. the command will read data from the channel until the eof is true. now listen — if you need to be able to process events during this calculation, go look at the PROGRAMMING INTERFACE section instead, bestie. that's your girl for that. 👀
• -filename name — this is the convenience option, the little shortcut queen. she 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. she cleans up after herself. we love that. 🎀
• -format string — return the checksum using an alternative format template. that's it, that's the vibe.
• -seed value — pick an alternative seed value for the CRC calculation. the default is 0xffffffff. this is genuinely useful for calculating the CRC for data structures without first converting the whole structure into a string — you can use the CRC of the previous member as the seed for calculating the CRC of the next member. iconic technique, fr fr.

⚠️ okay this part MATTERS. note that the crc32 algorithm includes a final XOR step. if incremental processing is what you want, 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 literally intended for this mode of operation. so like. just use that one. it's right there. she was made for this. 💜

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🌈 PROGRAMMING INTERFACE 🌈

so 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. (yes the original says "expecially" and i'm keeping it, it's part of the lore 🫶)

the way this slays is: 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. she's efficient AND pretty. main character energy honestly. ✨

::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 like it's your iced coffee. 🧊

::crc::Crc32Update token data

add data to the checksum identified by token. and here's the fun part — calling Crc32Update $token "abcd" is equivalent to calling Crc32Update $token "ab" followed by Crc32Update $token "cb". yes, "cb". that's what the original says. i am not making that up, i am simply reporting the facts with love. 💀 check the EXAMPLES section if you don't believe me.

::crc::Crc32Final token

returns the checksum value and releases any resources held by this token. once this command completes, the token will be invalid — she's done, she's retired, do not call her again. the result is a 32 bit integer value. 👑

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🍓 EXAMPLES 🍓

% 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?? same answer both ways!! the incremental girlies and the one-shot girlies are getting the SAME checksum. slay. 🔥

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⭐ AUTHORS ⭐

Pat Thoyts — the icon, the legend, the moment. 💜

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🙈 BUGS, IDEAS, FEEDBACK 🙈

okay so real talk, no sugarcoating: this document, and the package it describes, will undoubtedly contain bugs and other problems. it's fine. it's normal. it's software.

please report such in the category crc of the Tcllib Trackers at 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 want the ideas. we want them all. 🌸

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

💖 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. that's the whole procedure, bestie, you got this. 🫶

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🦋 SEE ALSO 🦋

• cksum(n)
• crc16(n)
• sum(n)

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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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and that's the whole page, bestie!! this little beauty lives in tcllib, version 1.3.4, and the page itself is dated to that same 1.3.4 release, filed under crc32(n). go checksum something and think of me. 💅✨🦋