Re: 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