Fast multidimensional Arrays

[rikki cattermole via Digitalmars-d-learn]

On 30/08/2016 1:02 AM, rikki cattermole wrote:
> On 30/08/2016 12:13 AM, Steinhagelvoll wrote:
>> Ok I added release and implemented the benchmark for 500 iterations,
>> 10000 are not reasonable. I build on the 2d array with LDC:
>> http://pastebin.com/aXxzEdS4 (changes just in the beginning)
>>
>> $ ldc2 -release -O3 nd_test.d
>> $ ./nd_test
>> 12 minutes, 18 secs, 21 ms, 858 μs, and 3 hnsecs
>>
>> , which is 738 seconds. Compared to (also 500 iterations)
>>
>> ifort -O3 -o fort_test test.f90 && ./fort_test
>>  time:    107.4640    seconds
>>
>>
>> This still seems like a big difference. Is it because I don't use a
>> continous piece of memory, but rather a pointer to a pointer?
>
> double[1000][] A, B, C;
>
> void main() {
>         A = new double[1000][1000];
>         B = new double[1000][1000];
>         C = new double[1000][1000];
>
>         import std.conv : to;
>         import std.datetime;
>         import std.stdio : writeln;
>
>         ini(A);
>         ini(B);
>         ini(C);
>
>         auto r = benchmark!run_test(10000);
>         auto res = to!Duration(r[0]);
>         writeln(res);
> }
>
> void run_test() {
>         MatMul(A, B, C);
> }
>
> void ini(T)(T mtx) {
>         foreach(v; mtx) {
>                 v = 3.4;
>         }
>
>         foreach(i, v; mtx) {
>                 foreach(j, vv; v) {
>                         vv += (i * j) + (0.6 * j);
>                 }
>         }
> }
>
> void MatMul(T)(T A, T B, T C) {
>         foreach(cv; C) {
>                 cv = 0f;
>         }
>
>         foreach(i, cv; C) {
>                 foreach(j, av; A[i]) {
>                         foreach(k, cvv; cv) {
>                                 cvv += av * B[j][k];
>                         }
>                 }
>         }
> }
>
> $ ldc2 test.d -O5 -release -oftest.exe -m64
> $ ./test
> 3 secs, 995 ms, 115 μs, and 2 hnsecs
>
> Please verify that it is still doing the same thing that you want.

Below change is slightly faster:

         foreach(i, cv; C) { 
 
 

                 foreach(j, av; A[i]) { 
 
 

                         auto bv = B[j]; 
 
 

                         foreach(k, cvv; cv) { 
 
 

                                 cvv += av * bv[k]; 
 
 

                         } 
 
 
                                      } 
 
 

         }