रञ्जित (Ranjit Mathew)A neat explanation:
“That XOR Trick” [2020], Florian Hartmann (https://florian.github.io//xor-trick/).
On HN: https://news.ycombinator.com/item?id=25821718 & https://news.ycombinator.com/item?id=44425880
The mother lode of #BitTwiddling tips (apart from the #book “Hacker’s Delight”, by Henry S. Warren Jr, and “HAKMEM” by the MIT hackers):
“Bit Twiddling Hacks”, Sean Eron Anderson (https://graphics.stanford.edu/~seander/bithacks.html).
This 👇🏽 is good 👌🏽:
“A Leap Year Check In Three Instructions”, Falk Hüffner (https://hueffner.de/falk/blog/a-leap-year-check-in-three-instructions.html).
Via HN: https://news.ycombinator.com/item?id=43999748
On Lobsters: https://lobste.rs/s/ybjgex/leap_year_check_three_instructions
#Optimization #Assembly #Compilers #GCC #Math #LeapYear #GregorianCalendar #BitTwiddling #Speed
Shane CelisI'm sure this has been done many times before, but I'm still happy to be bit-twiddling in #shaders. The star is this line:
(vertex_index & 3u) + (vertex_index >> 2u)
"Give me the first two bits but add one if the third bit is set.”
The shader generates a UV-mapped quad (right-triangle pair) from the 0 through 5 vertex indices. The screenshot code is abridged; full code is at the link.
https://github.com/shanecelis/bevy/blob/add-viewport-post-processing/crates/bevy_core_pipeline/src/viewport_vertex_shader/viewport.wgsl #gamedev #bevyengine #bittwiddling #wgsl
Kernel Bob 
In 2013, past me wrote some mysterious code. Effectively, it was this.
uint8_t decay(uint8_t x) { return (x >> 1) | (x >> 2); }
Sort of a low level multiply by 0.75, but with an | instead of a +. The target was an 8 bit AVR. Is there any good reason for using | here? I vaguely remember a bug where certain values didn't decay, but testing shows all 255 nonzero values of x do decay.
Any thoughts?
Blippy the Wonder Slug (MOVED)Re: coding.
If it ain't native ASM, it ain't shit.
POP!
**scampers away cackling maniacally**
Matthew FlintI made a tiny #Swift package for decoding Base32 values.
Nice – #RaymondChen is always a pleasure to read:
“On Finding The Average Of Two Unsigned Integers Without Overflow”, Raymond Chen (https://devblogs.microsoft.com/oldnewthing/20220207-00/?p=106223).
Via HN: https://news.ycombinator.com/item?id=30252263
#Arithmetic #Integers #Average #Mean #Overflow #BitTwiddling #Efficiency #Assembly
I’d like to think that Tarah’s colleague here was a master troll 🤡:
“A Bit Overcomplicated”, The Daily WTF (https://thedailywtf.com/articles/a-bit-overcomplicated).
Via HN: https://news.ycombinator.com/item?id=28072477
#Rust #Bit #Binary #Shift #BitTwiddling #Programming #WTF #Complexity
A Bit Overcomplicated
Lets say you have a 64-bit integer. You want the first 42-bits. Now, if your language has a bitshift operator, you'd be tempted to do something like largeNumber >> 22. But what if your language also has all sorts of advanced stream processing and map functions? It'd be a shame to not use those. Tarah's shop uses Rust, and thus they do have all those exciting advanced stream processing. Her co-worker decided they just needed to be used:
DewayneI'm working on a pure Ruby network packet encode/decode module using Array#pack and String#unpack. I did one of these about 16 years ago where everything was in one class. This time each format is a separate class like Uint8, Uint16, Uint32 and TimeStamp (which is a composite of 7 bytes) - with class methods encode and decode.
I'm kinda liking this current approach. Anyone do something similar? I'm expecting a little performance hit but frankly don't care at this point. #bittwiddling