A collection of notes and half-baked ideas and other things I wanted to write down to help clarify in my own mind or explain to somebody else.

## Posts

### Digging in to Pingback and Webmention

The other day I found out what a “Pingback” was, after I saw a bunch of them at the bottom of a widely-cited blog post. So I set about digging in to all that.

### Font-based digit grouping

A while back I got frustrated with struggling to read absurdly large numbers in terminal windows, and set about thinking how I might apply some logic in the terminal to subtly bunch together groups of three digits as a form of thousand separator. Eventually it occurred to me to try doing it in the font with ligature rules (initially as a joke, but then I looked into it) and it turns out Numderline is a thing which does that.

### Neighbourhood sampling order during texture filtering

During my tinkering with pixel-art scaling I found a source of noise which comes up when trying to use the derivative operations in shaders. It’s somewhat my own fault for doing thresholding excessively, but still…

### Scaling pixel art with SDF

For a while I’ve been wondering if giving a fantasy console like PICO-8 a graphics system defined in terms of more scalable low-memory primitives would lead to a more interesting retro style than the conventional sharp-edged squares. Not concepts like low-poly 3D or minified SVG (eg., RIPscrip), but maybe using pixel art scaling algorithms natively, or with additional markup in the data to clarify intent (sharpening corners, for example). Simply bake them into your pixel-art editor so you see what you’re going to get once it’s upscaled, with the option to correct it where it goes awry.

### Embedded web content without all that JavaScript cruft

In an earlier blog post I wanted to embed some diagrams. Really I wanted SVG for clean scaling between devices, but I don’t have that format as an output option.

### A pick-resistant lock design

There are a fair few attempts at “unpickable” locks out there, and overall I don’t think I have a great deal to add to the range of pre-existing methods. But a couple of years ago I thought I might have a go at my own design anyway.

### Error resilience in rolling-intra

Rolling intra is where a portion of each coded video frame is encoded without reference to any previous frame, guaranteeing that that part of the scene can be reconstructed when joining or re-joining a stream without previous context.

### Digits for a base-210 system

My own contribution to the field of making up improbable alien number systems involves counting in base 210. Rather than try to define 210 distinct symbols, or to make a 14-upon-15 or 15-upon-14 digit pair system, I chose to break each digit down into three components mod 5, mod 6, and mod 7.

### Optimising Adler-32 checksum

The Adler-32 checksum consists of two 16-bit sums. One is the sum of all the bytes in the data, plus one, and the other is the sum of all those intermediate sums, which works out to be the same as the sum of all the bytes multiplied by their distance from the end of the buffer plus the length of the buffer. Both modulo 65521.

### On the endianness of bitstreams

Where I’m from conventional wisdom has always been that while it’s an objective fact that little endian is the one-true-and-correct endian, bit-streams should always be packed as big-endian data.

### Curl is not secure by default

I often find that when there’s been some debate about a topic on the internet the conclusion might be a thorough debunking of a bad idea but also a failure to address a more nuanced idea – or sometimes even a more fundamental idea.

### What I've learned so far about CSS, SVG, Liquid, and Jekyll

From the point of view of knowing almost nothing about how any web techology works, here’s a bunch of stuff I had to pick up to draw a picture in a GitHub-powered blog.

### A Latin-Square-based L1 cache layout

If I were going to build some kind of fantasy machine I would not fuss about making it high-performance. Mine would just be a mash-up of random things I found interesting at some point.

### Bit-sliced matrix multiply

There’s a matrix multiplication in the middle of a lot of popular things, right now, and it’s an operation which frequently tolerates remarkably low precision.

### Pivot-sorting quick sort

Regarding those quick-sort variants which do things like median-of-k pivot selection before subdividing…

### Hash map reduction operations

I notice that some defaults for things like STL

`unordered_map`

are a bit scary. The function to reduce the range of the hash down to the size of the table is remainder, and the default hash for integers is the identity function.### A reasonably effective hash instruction

As per part one of this post, I have reasoned through and tested a proof of concept for generic CPU instruction which could achieve most of the required mixing of a good hash function in a single cycle (working with a combinational depth of 20 to 24 gates as a guide).

### Why I want a dedicated hash instruction

A good hash function is expected to remove correlations of various sorts between subsets of inputs and their hashed outputs in order to mitigate the risk of those correlations producing performance aberrations (cache collisions, unbalanced structures, etc.) or statistical biases.

### Idly musing over RowHammer mitigation strategies

Watching a RowHammer talk (slides) a while back (not actually the linked one, but I couldn’t find the one I attended) left me with a couple of thoughts about possible mitigations which I didn’t see discussed.

### N-bit Mixer Functions

For reasons I intend (hah!) to go into in a longer post I was looking for operations with which to construct and whiten (or “finalise” or “mix” or “avalanche” or whatever) RNGs with 2

^{n}periods. I was looking at splitmix64 which led me to Fast splittable pseudorandom number generators which cited Improving on MurmurHash3’s 64-bit Finalizer (although I found that page by other means) and finally MurmurHash3 which tells me where those constants and that construction both come from.### Minimally biased NPOT-ranged random numbers

In my previous post I described a technique for scaling random numbers to new intervals producing extremely small bias but with a constant execution time.

### Random number scaling

I’ve been doing some messing around with random number generation at work, and this inspired me to revisit something which has troubled me since my teenage years: Perfectly unbiased random numbers over a range which is not a power of two.

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