C on icyveins7's blog

Old dog, old C struct tricks

Mon, 14 Jul 2025 20:00:00 +0800

Look at this code snippet and tell me with a straight face you didn’t think it was a memory leak at first either..

A while ago I worked on some code which contained a container that looked like this:

struct S
{
 size_t sz;
 int data[1];

 void Set(size_t _sz, int *_data){
 sz = _sz;
 memcpy(data, _data, sizeof(int)*sz);
 }
}

If you’re a modern programmer like me, you might be looking at this and thinking: there’s no way this isn’t a flagrant memory violation in almost every case. Right? Well, it turns out this is something them old boys before C99 used to do.

Gotta go (randomly) fast, thrust vs cuRAND

Mon, 10 Mar 2025 20:00:00 +0800

How fast can you generate (pseudo-)random numbers on the GPU? How fast can you generate (pseudo-)random numbers on the GPU?

I recently had to answer this question. Well, not exactly this question, but this was a key part of it.

A quick google search will bring up two common methods (libraries) when trying to do this in CUDA: thrust and cuRAND. Thrust is known to be a lot easier to set up; no need to write the kernel code and nitty gritty details, so I started with that.

Cross-platform trigonometric SIMD and how the C ABI confused me

Thu, 30 Jan 2025 20:00:00 +0800

My small journey in discovering libmvec functions and the C problems I encountered..

I was recently working on making an existing Windows-only library of SIMD functions cross-platform i.e. making everything work in Linux. Here I’m going to highlight some problems I encountered in the process; hopefully it will help someone if they encounter something similar too.

The Windows (MSVC) function

Intrinsics are usually tied to compiler implementations. The one that gave me issues was a bunch of trigonometric functions. Let’s use the SSE version that works on floats; in MSVC this was implemented as a simple