Posted by jpluimers on 2021/08/05
There is a known saying phrased using cardinal, adverbial or ordinal numbers, and several naming for the first:
Sometimes the second can lead to a pattern.
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Posted by jpluimers on 2021/07/16
Everyone can learn from an outage. CloudFlare shows how to do it right, for instance on the RegEx-going-wild downtime 2 years ago.
So it’s time to link to that one again: [WayBack] Details of the Cloudflare outage on July 2, 2019
More like these at [WayBack] Post Mortem – The Cloudflare Blog.
More on evaluating regular expressions in linear time:
A method for locating specific character strings embedded in character text is described and an implementation of this method in the form of a compiler is discussed. The compiler accepts a regular expression as source language and produces an IBM 7094 program as object language. The object program then accepts the text to be searched as input and produces a signal every time an embedded string in the text matches the given regular expression. Examples, problems, and solutions are also presented.
Programming Techniques: Regular expression search algorithm
Full Text:
Author: Ken Thompson Bell Telphone Labs, Inc., Murray Hill
Published in:
· Magazine Communications of the ACM CACM Homepage archive Volume 11 Issue 6, June 1968
Pages 419-422
ACM New York, NY, USA
table of contents doi>10.1145/363347.363387
is a method of transforming a regular expression into an equivalent nondeterministic finite automaton (NFA)
The algorithm works recursively by splitting an expression into its constituent subexpressions, from which the NFA will be constructed using a set of rules.[3] More precisely, from a regular expression E, the obtained automaton A with the transition function δ respects the following properties:
- A has exactly one initial state q0, which is not accessible from any other state. That is, for any state q and any letter a, {\displaystyle \delta (q,a)} does not contain q0.
- A has exactly one final state qf, which is not co-accessible from any other state. That is, for any letter a, {\displaystyle \delta (q_{f},a)=\emptyset }.
- Let c be the number of concatenation of the regular expression E and let s be the number of symbols apart from parentheses — that is, |, *, a and ε. Then, the number of states of A is 2s − c (linear in the size of E).
- The number of transitions leaving any state is at most two.
- Since an NFA of m states and at most e transitions from each state can match a string of length n in time O(emn), a Thompson NFA can do pattern matching in linear time, assuming a fixed-size alphabet.
Via [WayBack] Details of the Cloudflare outage on July 2, 2019 | Hacker News
–jeroen
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Posted by jpluimers on 2021/07/15
For my link archive: [WayBack] c# – Algorithm to check whether a certain hour falls into a given time period – Stack Overflow answered by [WayBack] kennytm:
Assume you only have the time and not the date.
if end_time >= start_time: return start_time <= current_time <= end_time else: return start_time <= current_time or current_time <= end_time
I totally agree with this comment:
This is brilliant! Thanks a lot. – Martin Dimitrov [WayBack]
I love it when algorithms are simple and elegant.
It reminded me of another scheduling related algorithm: [WayBack] Activity Selection Problem | Greedy Algo-1 – GeeksforGeeks
–jeroen
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Posted by jpluimers on 2021/06/22
I originally posted this in a docker on docker thread, but I think it holds universally:
[WayBack] Jeroen Pluimers on Twitter: “Not having done docker, but having developed enough software to have the impression that as soon as things get hierarchical, things eventually end up in a mess. Somewhere down the road something won’t cope with depth/breadth/size and break badly.”
This despite the cool gif in the reply:
[WayBack] Duffie Cooley on Twitter: “… “
I found the below video files by searching for zzzz
Original thread start:
[WayBack] Duffie Cooley on Twitter: “When you hear Docker in Docker what do you think of? docker socket: Mounting in the underlying docker.sock and allowing a container to make new containers. kernel privs: Giving enough privs to a new container that it can make new containers cause it shares a kernel.”
–jeroen
Posted in Algorithms, Cloud, Containers, Development, Docker, Infrastructure, Kubernetes (k8n), Software Development | Leave a Comment »
Posted by jpluimers on 2021/05/13
A while ago I needed an estimate for [WayBack] How to calculate bitmap size? – Stack Overflow, which does an accurate calculation for the size of the pixel storage (i.e. without headers):
pixelStorageSize = (( width*bitsPerPixel + 31) / 32) * 4 * height
Here:
It was derived from [WayBack] Capturing an Image – Windows applications | Microsoft Docs and shorthand for what is explained at [WayBack] BMP file format: Pixel storage – Wikipedia
The bits representing the bitmap pixels are packed in rows. The size of each row is rounded up to a multiple of 4 bytes (a 32-bit DWORD) by padding.
For images with height above 1, multiple padded rows are stored consecutively, forming a Pixel Array.
The total number of bytes necessary to store one row of pixels can be calculated as:
- {\displaystyle {\text{RowSize}}=\left\lceil {\frac {{\text{BitsPerPixel}}\cdot {\text{ImageWidth}}}{32}}\right\rceil \cdot 4=\left\lfloor {\frac {{\text{BitsPerPixel}}\cdot {\text{ImageWidth}}+31}{32}}\right\rfloor \cdot 4,}
- ImageWidth is expressed in pixels, note the special parentheses.
The total amount of bytes necessary to store an array of pixels in an n bits per pixel (bpp) image, with 2ncolors, can be calculated by accounting for the effect of rounding up the size of each row to a multiple of 4 bytes, as follows:
- PixelArraySize = RowSize · |ImageHeight|
- ImageHeight is expressed in pixels. The absolute value is necessary because ImageHeight can be negative.
I think I needed this to estimate how many bitmaps would fit in
[WayBack] Virtual address space – Wikipedia, which on 32-bit Windows by default is limited to 2 GiB, and can be extended to 3 GIB by enabling the IMAGE_FILE_LARGE_ADDRESS_AWARE executable header flag.
This flag imposes the risk of many libraries and DLLs to fail because they do not get the pointer math right. You often do not have control of future versions of DLLs being loaded in your process space and their risks, so do not ever use that flag.
–jeroen
Posted in Algorithms, Development, Software Development | 1 Comment »
Posted by jpluimers on 2021/04/07
For past timestamps (or date-times), as long as you know the associated location, you always know the time zone rule that applies, no matter if you store them in UTC or local time zone.
For future dates, UTC might not be the best option, as you have no knowledge on future time zone rules. There you need to have at least three fields:
Posted in .NET, Algorithms, Development, Jon Skeet, Software Development | Leave a Comment »
Posted by jpluimers on 2021/03/18
Originally created for anime upscaling, the waifu2x algorithm works very well for photos, logos and text.
It is open source too!
More information:
rewritten for Windows, using Caffe to rewrite only the conversion function of the image conversion software ” waifu2x ” . It can be converted by CPU, but it can be converted faster than CPU by using CUDA (or cuDNN).
GUI supports English, Japanese, Simplified Chinese, Traditional Chinese, Korean, Turkish, Spanish, Russian, and French.
–jeroen
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Posted by jpluimers on 2021/03/10
TL;DR of https://css-tricks.com/debouncing-throttling-explained-examples/:
- debounce: Grouping a sudden burst of events (like keystrokes) into a single one.
- throttle: Guaranteeing a constant flow of executions every X milliseconds. Like checking every 200ms your scroll position to trigger a CSS animation.
- requestAnimationFrame: a throttle alternative. When your function recalculates and renders elements on screen and you want to guarantee smooth changes or animations. Note: no IE9 support.
Full article [WayBack] Debouncing and Throttling Explained Through Examples | CSS-Tricks
Delphi implementations:
PDF
TObservable.FromEventPattern(Edit1, 'OnChange');
.Throttle(1000)
.ObserveOn(TScheduler.MainThread)
.Subscribe(
procedure(const args: TNotifyEventArgs)
begin
Caption := Format('searching for %s', [TEdit(args.Sender).Text]);
end);
–jeroen
Posted in Algorithms, Delphi, Development, JavaScript/ECMAScript, Scripting, Software Development | Leave a Comment »
Posted by jpluimers on 2021/02/24
Edit 20260622: added Nitter¹ links, queries, the TEX map, LISTSERV dump and 1987+1988 lists of USENET nodes (some bit BITNET, others via UUCP).
In a response to [WayBack/Archive] Iris Classon on Twitter: “I’m curious, how many of you guys and gals have printed out code on paper to read later? Doing it during earlier years also counts 🤓”, I started the long read below starting with [WayBack] Jeroen Pluimers on Twitter: “Still do.… “ or [Wayback/Archive] Iris Classon | Author & programmer (@IrisClasson): “I’m curious, how many of you guys and gals have printed out code on paper to read later? Doing it during earlier years also counts 🤓” | nitter.
The reactions show quite a bit of history (:
Basically my response was a more in depth coverage of my 2017 post Happy 60th birthday, Fortran.
Posted in Algorithms, Development, Fortran, Power User, Printers, Software Development | Leave a Comment »
Posted by jpluimers on 2020/06/24
From about 4 years ago, so time to see how many development stacks support Unum by now: [WayBack] The End of (Numeric) Error
Crunching numbers was the prime task of early computers. The common element of these early computers is they all used integer arithmetic. John Gustafson, one of the foremost experts in scientific computing, has proposed a new number format that provides more accurate answers than standard floats, yet saves space and energy. The new format might well revolutionize the way we do numerical calculations.
Back then, I found these links through my G+ circles:
Posted in Algorithms, Development, Floating point handling, Software Development, Unum | Leave a Comment »
The Wiert Corner - irregular stream of stuff 