Some files that you download will come with a .sfv file.
This is used to verify that the files that you received are the same as
the originals.

cksfv (Check SFV) is a program that can use the .sfv file to verify the
downloaded files. Also, it can be used to create new .sfv files.

cksfv is a command line tool that uses crc32 checksum to verify file 
integrity. .sfv is simple file verification. 

There is a script to integrate this tool with GNOME's Nautilus file
manager, but since GNOME isn't included in Slackware, it is included
as part of the documentation instead of in the normal location.
You can install it on your own or modify the SlackBuild script to
do so. It can be found under the "./scripts" directory of the source
code, and is called CheckSFV in the resulting package's documentation
directory. All you need to do is to copy the "CheckSFV" file to
$HOME/.gnome2/nautilus-scripts