Summation of double using the processor's floating-point instruction set

Question

On a Windows machine with Intel Core-i5, I want to write ac# program which sums an array of double at highest possible speed , which in fact means using the instruction set of the built-in FPU.

double[] arr = new double[] { 1.123, 2.234, 3.1234, .... };

The processor has a built-in command which can sum up a whole memory array ("vector") with one single command. Is there a way in C# to execute the summation with this built-in machine command? ( I mean, besides writing unmanaged assembly code)

EDIT: Or is there a library call which will do this ?

Answer 1

No. You can't directly use SSE/AVX/... instructions in C#. You could write some C++ code and PInvoke it, but probably the PInvoke cost would remove all the benefits of using these instructions.

Technically you can do bad things and call these instructions from C# (see https://stackoverflow.com/a/29646856/613130 ), but they are bad slow things , so you wouldn't probably gain anything speedwise.

Answer 2

Yes, there are several ways to accomplish this

double sum = arr.Sum();

which uses Linq to sum the array. This is the simplest way, but is not the highest possible speed way. You asked about a library call that can do this, HPCsharp is such a library: nuget package available on nuget.org. The fastest implementation there is

double sum = arr.SumSsePar();

which uses SIMD/SSE instructions to get the most performance out of each core, and uses multiple cores to get the highest performance out of the processor.