Simplest way to use SIMD for basic float multiplication/addition?

[mikej]

@mikej

h implementing a third party library like this one or is there any other you would recommend?

Thanks. I didn’t realize SIMDRegister like that has 4 floats in it. Based on your tip, I found a simple example of how to use it here:

SIMDRegister - How do I do the equivalent of

Just for the record, although people are tolerent of quite messy looking SIMD code because so much of it looks like that, it doesn’t have to be so bad if you use a more modern style, e.g. the example above using SIMDFloat = SIMDRegister<float>; alignas (16) float vraw[] = { 0.0f, 2.2f, 1.3f, 19.9f }; SIMDFloat v = SIMDFloat::fromRawArray (vraw); SIMDFloat p (2.3f); SIMDFloat u = v + p; alignas (16) float eraw[4]; u.copyToRawArray (eraw); DBG (eraw[1]); could be written as simply as this: auto…

I will try that soon.

The funny thing about all this is it requires you to:

• create a new (aligned) array of the primitives (floats)
• put that array into a new class to get it into the SIMD format.
• do this twice if you need to multiply two sets of data
• multiply the SIMD types (only step saving operations)
• create a new (aligned) array to copy the data to or run a get function for each

It seems surprising to me this is any better than just multiplying but I guess multiplying is still much more expensive than shuffling all these primitives around.

Also, in the example given, is the alignas (16) necessary? Eg.

alignas (16) float eraw[4];
u.copyToRawArray (eraw);

What would happen if you didn’t have the alignas? Would it just fail?

I notice Jules’ code skips all this completely. Is it likely less/more or the same efficiency to use:

float val0 = u.get(0);
float val1 = u.get(1);
float val2 = u.get(2);
float val3 = u.get(3);

Thanks for any further thoughts.