Notes on LHARK compression format

LHARK (with a K) is an old compression/archiver utility for DOS. It is related to the popular utility named LHA (formerly LHarc), but should not be confused with it. You should be able to find a copy of LHARK by searching the web for "LHARK04D". LHARK was developed by Kerwin F. Medina around 1995/1996. It …

The Cleveland baseball team

I see that the Cleveland Indians baseball team is finally going to change their nickname. I think that's probably a good thing. For one thing, the word "Indians" is ambiguous, and you wouldn't want to accidentally demean people from South Asia, when you're trying to demean people from North America. They say they haven't chosen …

The blocksize field in LHA compression format

This post is about the data compression format I'll call "lh5". It is actually a family of formats that includes the compression methods often named lh{4, 5, 6, 7, 8}. It was most notably used by version 2.x of the old LHA/LZH/LHArc compressed archive format. It was used, often in modified form, in a number …

Overview of some simple map projections

Some lists of map projections cover them in a way that I think is more haphazard than it needs to be. This is my attempt at a simple introduction to some map projections. I'll only look at the usual situation, in which we are mapping the surface of a sphere onto a planar map. The …

LZ77 compression prehistory

LZ77 is a widely-used class of data compression algorithms. I'll start with a quick overview of it. Assuming you're compressing a stream of bytes (a "file"), your LZ77 compressed data, at a high level, would contain two possible kinds of instructions for the decompressor: Emit literal: {byte value=A}Copy from history: {match-offset=B, match-length=C} The match-offset may …

An obscure polyglot file: LHA/CAR

LHA is a compressed archive file format and compression utility that was, for a long time, a competitor of ZIP. It's also known as LZH format, or LHarc format, but I'll call it LHA. In the course of researching it, I came across an obscure lookalike format created by a program named CAR. CAR is …

Earth portrait photos

This is a pretty good photograph: … Though it's so ridiculously overused and cliché that it surprises me that graphic designers, etc., still seem to like using it. Maybe we've been so thoroughly conditioned by it that other photographs of the Earth just don't look like we think the Earth is supposed to look. If …

Alternative to Cantor’s diagonalization argument

How does one prove that there are more real numbers than integers? There are an infinite number of each, but the infinity of the real numbers is, in a strict sense, larger than the infinity of the integers. In math terminology, the set of reals has a larger cardinality. Roughly speaking, it's equivalent to saying …

Thoughts on timestamps of computer files

Computer files can have a number of different kinds of timestamps. Some of them are stored in the file's external metadata, alongside the file's name -- I'll call these external timestamps. Others are stored inside the file itself -- I'll call these internal timestamps. I use the term "timestamp" loosely. When something called a "timestamp" …

Win32 I/O character encoding supplement 1 – A Cygwin issue

A while back, I wrote a series of posts about using Unicode in Windows console mode programs: Part 1Part 2Part 3 In Part 2, I said that programmers should probably not be changing the console code page to UTF-8 (65001). And that if they must, they should change it back when they're done. But now …