Notes on WinHelp format, part 2

This post is part of a series about WinHelp file format. Part 1 - Read this first.Part 3 The internal TOPIC file (named "|TOPIC") is the business part of the HLP file. It contains the text, and other information. To read the TOPIC file, you need to know the TOPIC "block size", which will be …

Another Implode bug in old PKZIP software

In a previous post, I discussed an old PKZIP bug related to the compression method named "Implode". I'll call that bug the "MML bug", for "Minimum Match Length". [See also a later post: Bug #3.] In this post, I'll discuss another old PKZIP bug related to Implode compression, mainly just to distinguish it from that …

Notes on WinHelp format, part 1

I wanted to write a program to extract the text from WinHelp .HLP files. HLP format was the standard Microsoft Windows help/documentation file format from around 1990 (the start of the Windows 3.x era), through the early 2000s. There are countless old Windows applications that come with an HLP file, but starting with Vista, Windows …

What is the name of libjpeg?

Shortly after the development of the JPEG image format around 1991, an organization named the Independent JPEG Group (IJG) released an open source software package to help people use the format. While the software included a few utilities, such as cjpeg and djpeg, the important part of it was its C library. The library became …

When was the Earth formed?

When was the Earth formed? Modern estimates are that it formed by accretion, 4.54ish billion years ago. But I'm not going to worry about its absolute age; what I'm wondering is where we choose to draw the line between Earth-not-quite-formed and Earth-now-formed. We don't really know how long it took for the Earth to form. …

Why is a ______ tax fair?

Certain types of people like to ask the question "Why is a progressive tax fair?" The inevitable answer given is "marginal utility!" The theory is that if a rich person and a poor person both have to pay an extra 50 spacebucks (or whatever currency is used in your realm) in taxes, it doesn't reduce …

Investigating an UnZip decompression bug

One of the old compression methods for ZIP format is named "Shrink". In the process of writing my own Shrink decompressor, I came across a problem with the Info-ZIP UnZip software. It's triggered by a small percentage of Shrink-compressed files. As an example, I'll use the file that you can download here: BLING.WAV. Now, in …

Are you a group selectionist?

Many scientifically-minded people believe in the evolutionary concept of group selection, without knowing that the thing they believe in has a name, or that it is, at best, disputed. Standard disclaimer: Just because I may suggest that something is scientifically true or natural, does not mean that I consider it to be morally good. So, …

Spooky action and quantum marbles

There's a phenomenon in quantum mechanics popularly known as "spooky action at a distance". One manifestation of it is known as the EPR paradox. It's usually explained using a thought experiment similar to the following. Spooky action at a distance "explained" Start with a particle that has a total "spin" of zero. Allow it to …

PKZIP “Implode” compression oddity

When I was researching old versions of PKZIP, I found that modern unzip programs aren't able to unzip the PKZIP v1.01 distribution file. Three of the member files inside the self-extracting ZIP file fail to decompress correctly. /cygdrive/c/dosprogs/ZIPTEST/101 $ unzip ../DIST/PKZ101.EXE exploding: README.DOC warning: 475 bytes required to uncompress to 873 bytes; supposed to require …