Bits, Math and Performance(?)

Given some black-box permutation that operates on an array of integers, it's easy to find out what the permutation does: feed it an ...

After browsing some articles about Fenwick trees (aka Binary Indexed Trees) and seeing remarks such as "let f be some group operat...

What is abs(x - y) , why do I even bother asking a question like that, much less answer it? Trust me, it's more interesting than it ...

Before we go any further, the answer is (usually) -N % N . "Usually", because for example MSVC with "SDL checks" ...

Let's say that we have a graph of at most 8 nodes (you can also think of it as a relation between 8 things), represented as an 8 by ...

The basic trick to apply the same bit-permutation to each of the u32 s is to view them as matrix of 16 rows by 32 columns, transpose it...

A while ago, after some back and forth on twitter/X with @corsix , I dropped some implementation of byte histogramming without explain...

Part 2 of Enumerating all mathematical identities (in fixed-size bitvector arithmetic with a restricted set of operations) of a certain ...

I was reminded (on mastodon) of this nibble-sorting technique (it could be adapted to other element sizes), which I apparently had only ...

I have written about this before , but that was a long time ago, I've had a lot more practice with similar things since then. This ...

This is a relatively simple use of GF2P8AFFINEQB . By itself GF2P8AFFINEQB essentially multiplies two 8x8 bit-matrices (but with trans...

As a reminder, grev is generalized bit-reversal , and performs a bit-permutation that corresponds to XORing the indices of the bits of ...

Once again a boring-but-specific title, I don't want to clickbait the audience after all. Even so, let's get some "disclaim...

popcnt(x) < tzcnt(x) asks the question "does x have fewer set bits than it has trailing zeroes". It's a simple quest...

The partial sums of popcount , aka A000788: Total number of 1's in binary expansions of 0, ..., n can be computed fairly efficiently...