(Sub)bit-fields (Coding with fractions of bits, Part II)

August 13, 2019

Last week, we used the 6×7×6 palette as an example of very simple fraction-of-a-bit coding1. However, we can generalize still a bit more to allow single field extraction and modification

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Ohta (Colorspaces III)

April 24, 2018

Let’s continue with lesser known color spaces. In 1980, Yu-Ichi Ohta [1] to segment images based on colors, and to do this, introduced a new colorspace—or more precisely, two variants of the same color space.

Ohta’s concern wasn’t image coding but region separation. He supposed (without much evidence) that a color space with a basis close to the principal components of the colors in the image should be maximally discriminant. He then proposed that the colorspace

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Yes? No? Maybe? (Part II)

March 27, 2018

Last week, we had a look at how to implement a trool, or a tri-valued boolean what accepts true, false, and undefined. We remarked that the storage of an enum likely defaults to int, and that my poc wouldn’t play well with std::vector as that container has no specialization to deal with this new type.

A specialization would be interesting because we can do much better than using an integer to store three different values. We can do much, much better.

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Pretty Printing a Tree in a Terminal

December 6, 2016

More often than I’d like, simple tasks turn out to be not that simple. For example, displaying (beautifully) a binary tree for debugging purpose in a terminal. Of course, one could still use lots of parentheses, but that does not lend itself to a very fast assessment of the tree. We could, however, use box drawing characters, as in DOS’s goode olde tymes, since they’re now part of the Unicode standard.

tree-01

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Serializing Trees

September 6, 2016

Quite a while ago I discussed using flat arrays and address calculations to store a tree in a simple array. The trick wasn’t new (I think it’s due to Williams, 1964 [1]), but is only really practical when we consider heaps, or otherwise very well balanced trees. If you have a misshapen tree, that trick doesn’t help you. It doesn’t help you either if you try to serialize a misshapen tree to disk.

But what if we do want to serialize arbitrarily-shaped trees to disk? Is it painful? Fortunately, no! Let’s see how.

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Interpolation Search

January 19, 2016

We all know about binary search. It’s been with us such a long time. Knuth thinks it’s first appearance in print is in the Moore School Lectures, in 1946. The technique search for an item in a list by halving, iteratively, the searched portion. Its complexity is O(\log n) for a list of n values, making it a very efficient algorithm for searching.

One may even be tempted to think that it’s in fact optimal, that we can’t do significantly better. Is that so?

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A Bit About Bit-Fields

January 5, 2016

Let’s make a detour through low-level programming this week. Let’s talk about bit-fields and some of their quirks.

amonite

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