In the previous part we ended with a nifty way of computing the last bit of a mask using the prefix sum. The key of the approch is based on the fact that the last element of the prefix sum of a mask is either the population count or population count minus one.

Let’s prove that using Lean.

The RISC-V Vector Extension (RVV) includes several instructions to operate on masks and compute interesting things. One of them is vfirst.m that computes the lowest-numbered element of the mask that is set.

However, there is no vlast.m instruction that computes the highest-numbered element of the mask that is set.

In my day job sometimes I need to edit documents using tools that are only available on Windows. As such, I have a virtual machine with Windows 10 running on VirtualBox.

Recently I upgraded to Debian 13 and I took the opportunity to migrate to a libvirt-based solution. I explain here the steps that I followed.

Most programming languages, including C and C++, provide language runtime libraries that implement parts of the language itself. These libraries must be linked in the final program or shared library.

Today we are going to see how an unfortunate default in the way shared libraries work in Linux can make our lives a bit more complicated than they have to if the language runtimes are in static libraries.

A common task in imperative programming languages is writing a loop. A loop that can terminate requires a way to check the terminating condition and a way to repeatedly execute some part of the code. These two mechanisms exists in many forms: from the crudest approach of using an if and a goto (that must jump backwards in the code) to higher-level structured constructs like for and while ending in very high-level constructs built around higher-order functions in for_each-like constructs and more recently, in the context of GPU programming, the idea of a kernel function instantiated over a n-dimensional domain (where typically n ≤ 3 but most of the time n = 1).

These more advanced mechanisms make writing loops a commonplace task and typically regarded as uneventful. Yet, there are situations when things get subtler than we would like.