Playing SIMD

[Andrei Alexandrescu via Digitalmars-d]

On 10/25/2015 03:37 PM, Iakh wrote:
> Here is my implementatation of SIMD find. Function returns index of
> ubyte in static 16 byte array with unique values.
>
> ------
> immutable size_t ArraySize = 16;
> int simdIndexOf(ubyte niddle, ref const ubyte[ArraySize] haystack)
> {
>      ubyte16 arr;
>      arr.array = haystack[];
>      ubyte16 niddles;
>      niddles.array[] = niddle;
>      ubyte16 result;
>      result = __simd_sto(XMM.PCMPEQB, arr, niddles);
>      alias Mask = ulong;
>      static assert(2 * Mask.sizeof == result.sizeof);
>      immutable BitsInByte = 8;
>
>      if (Mask mask = *cast(Mask*)(result.array.ptr))
>      {
>          return bsf(mask) / BitsInByte;
>      }
>      else if (Mask mask = *cast(Mask*)(result.array.ptr + Mask.sizeof))
>      {
>          return bsf(mask) / BitsInByte + cast(int)Mask.sizeof;
>      }
>      else
>      {
>          return -1;
>      }
>
> }
> ------
>
> Is it optimal and how do you implement this stuf?
>
> Full exaple with comparation of algorithms (SIMD, naive, binary search):
> http://dpaste.dzfl.pl/f3b8989841e3
>
> Benchmark result on dpaste.dzfl.pl:
> SIMD:   TickDuration(157000)
> Binary: TickDuration(472000)
> Naive:  TickDuration(437000)
>
> At home with defult dub config "dub run --build=release":
> SIMD:    TickDuration(241566)
> Binary:  TickDuration(450515)
> Naive:   TickDuration(450371)

This is compelling but needs a bit of work to integrate. Care to work on 
a PR that makes std.algorithm use it? Thanks! -- Andrei