Details of Okumura’s LZSS compression

In this post, I'll write something like a specification for the compressed data format we might name "Okumura's LZSS". I'll shorten the name to just "LZSS", but be advised that "LZSS" can have a much broader meaning in general. The audience is someone who already has a basic understanding of "LZSS" and "LZ77" compression. I've … Continue reading Details of Okumura’s LZSS compression

Notes on PFS:First Publisher ART format

For today's exercise in digital archeology, I'm taking a look at the simple bitmapped graphics file format commonly called something like PFS:First Publisher ART. PFS:First Publisher is a desktop publishing program, dating back to 1987. The relevant versions of it are for MS-DOS. ART is not the main file format used by the software; it's … Continue reading Notes on PFS:First Publisher ART format

My two cents, rounded down, on pennies

It's been my opinion for a long time that the United States should phase out the penny, at least for transactions larger than a dollar or two. And now, finally, it's happening! Correction: Something's happening, but it's not really that. As of this writing, what has happened is that the Treasury Department has unilaterally decided … Continue reading My two cents, rounded down, on pennies

The dates of earliest sunset and latest sunrise

If you're in the northern hemisphere, and south of the Arctic Circle, the shortest day of the year happens right around the December solstice. (In this context, the length of the day is the amount of time during which at least part of the sun is visible above the horizon.) I think that many people, … Continue reading The dates of earliest sunset and latest sunrise

Notes on ZIP format and disk spanning

One of the dark corners of ZIP file format is the "multi-segment" archive feature. By "multi-segment archive", I mean to include the disk spanning features intended for floppy disks, and the slightly more general case of "split archives", which was added to the format documentation around the year 2000. The idea is, what would normally … Continue reading Notes on ZIP format and disk spanning

The supernovas that get no respect

Astronomers and other communicators of popular astronomy often tell us that the most recent supernova seen in our own Milky Way galaxy was Kepler's Star, also named SN 1604, in the year 1604. (Obviously, dates like this are based on when the light from them could have reached Earth.) Estimates of the frequency of supernovas … Continue reading The supernovas that get no respect

The “file” command: annotations

This post is part of a series. For an introduction to the file command, and the other posts in the series, see the first post. When writing a "magic pattern" file for the file command, you can include some special lines that start with "!:". The documentation doesn't name this feature, but I'll call it … Continue reading The “file” command: annotations

The “file” command: binary and text files

This post attempts to explain a few things about how the file command deals with binary vs. text files, primarily from the standpoint of someone writing "magic patterns" for it. For an introduction to the file command, and my other posts on the topic, see the first post. Note that by "ruleset", I mean a … Continue reading The “file” command: binary and text files