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Comment by eachro | Hacker News Reader

There's "knowing C syntax" and then there's knowing C well enough to be able to read this code and understand what's going on. One of these days I'd like to get to the point where I can conceivably read this code and understand it well enough to build my own matrix library using similar optimizations for the rest of the matrix operation primitives. Some day ...

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Intrinsics-heavy code does looks scary because you see tons of weirdly-named functions with no clue as to what they do.

However, you can learn the basics in an hour, and read/write small amounts of code (like in the article) very quickly. The trick that you don't learn all those functions, instead you constantly use the amazing interactive guide:

https://www.intel.com/content/www/us/en/docs/intrinsics-guid...

I guess real pros do memorize the API of course, but I have written many (<1000) lines of intrinsics code like this.

PSA the database of instructions and intrinsics is in this xml file

https://www.intel.com/content/dam/develop/public/us/en/inclu...

This code is less about knowing C and more about knowing vector intrinsics which are not standard C. The actual code is mostly straightforward constructs.

Interestingly knowing vector intrinsics is exactly what optimising compilers are good at.

The article even shows that - look at the C++ code - no instrisics in sight, just pure basic C++ getting the optimisation and performance from the compiler alone.

You probably want to look at the kernels themselves: https://github.com/HazyResearch/blocking-tutorial/blob/maste...

I was referring to https://github.com/HazyResearch/blocking-tutorial/blob/maste... which upon closer inspection uses intrinsics in the inner loop, but to a much lesser degree and arguably specifying -mavx2 -mfma compiler options would yield comparable results...

That’s the timing harness for the more advanced implementations, I think.

Yes, GCC fully vectorizes (and unrolls) a micro-kernel loop nest.

Each architecture has a "library" of these bizarrely named functions that are mapped by the compiler to CPU-specific instructions. I'd suggest 90%+ of C programmers couldn't name a single one of them, and that's fine, because they have no place in C outside of tight platform-specific optimization work, which very few people have a need for or mandate to actually work on

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