Editing mirc/identifiers/$crc

{{mirc title|$crc Identifier}}'''$crc''' calculates the [[32-bit checksum]] of a text, {{mirc|binary variables|binary variable}}, or file. Hash is 32-bits, shown as 8 upper-case hexadecimal characters.


== Synopsis ==
<pre>$crc(plaintext|&binaryvar|filename[,N])</pre>

== Parameters ==
'''plaintext''' - Used with N = 0, just the string you want the CRC-32 checksum hash of

'''&binaryvar''' - A binary variable, used with N = 1, return the CRC-32 checksum of the content of the binary variable

'''filename''' - A filename, used with N = 2, return the CRC-32 checksum of the content of the file

'''N:''' Optional integer 0-2, where 0 indicates data is treated as plaintext, 1 indicates a &binary variable, 2 treats data as contents of a filename<br />

If the N parameter isn't used, the default 2 is used (which is different than $sha1 which has default of N=0.) Also different than $sha1, invalid N outside 0-2 range are treated as default 2 instead of creating an error.

== Properties ==

None

== Example ==
Echo the $crc hash of plain text string ''abc'' to the active window:
<pre>//echo -a $crc(abc,0)
</pre>
The DATA is case-sensitive, so hash of "abc" is different than hash of "ABC"

Echo the CRC-32 hash of the first 1000 bytes of the mIRC program you're running to the active window:
<pre>//bread $qt($mircexe) 0 1000 &snip | echo -a $crc(&snip,1)</pre>

Echo the CRC-32 hash of the contents of the mIRC program you're running to the active window:
<pre>//echo -a $crc($mircexe,2)
or
//echo -a $crc($mircexe)
</pre>

Returns 00000000 if filename does not exist:
<pre>//echo -a $crc(no_such_file.txt,2)

Suggested Uses:
* Quick way to compare if 2 files are identical. (First check should always be comparing file sizes.)
* Quick way to check if a file's contents have changed since stored CRC checksum was made.
* Verify downloaded file hasn't been corrupted, matches the sender's original.
<br />
Note that because the default is N=2, '''$crc(versions.txt)''' is the CRC-32 for the contents of versions.txt (or 00000000 if the file doesn't exist). This differs from $sha1(versions.txt) giving the hash of the plaintext inside the parenthesis because $sha1 has default of N=0.<br />
mIRC v7.x Unicode-encodes plaintext before providing to $crc, so v7.x and v6.x return different answers for //echo -a $crc($chr(233),0)<br />

If the text doesn't have Unicode code points above 255, to avoid having Unicode points 128-255 encoded to 2-byte pairs, the text must be fed to $crc as a binary variable:<br />

<pre>//bset -ta &string 1 chloé | echo -a $crc(&string,1)</pre>

== Error Messages ==
None

$crc differs from $sha1 in that it returns no error messages.

For non-existent filenames, it returns 00000000 instead of halting script with an error.
For calculating hash of $null string it returns nothing instead of the checksum of the null-string
When given invalid N outside the 0-2 range, it uses default 2 instead of halting script with an error.

== Compatibility ==
For $crc(filename):
{{mIRC compatibility|5.6}} 
For N=0-2 parameter:
{{mIRC compatibility|6.1}} 

== See also ==
* {{mIRC|$sha1}}
* {{mIRC|$md5}}
* {{mIRC|$sha256}}
* {{mIRC|$sha384}}
* {{mIRC|$sha512}}
* [[List of identifiers - mIRC]]
{{mIRC identifier list}}
[[Category:mIRC identifiers|crc]]