You see a bit of this in game development. At my old job, our engine was written in C++, however we had two copies of our matrix library: one written in C for d

You see a bit of this in game development. At my old job, our engine was written in C++, however we had two copies of our matrix library: one written in C for desktop etc. and one written in ARM NEON asm, for building on iOS or with the Android NDK.