static arrays.

[Dave]

Whoops - I should have made it clear that the programs perform roughly the same (D being about 10% 
faster), but only if the static matrices are passed byref (using pointer params) in D.

For Delphi, static arrays are passed byref.

Dave wrote:
> 
> Static ("rectangular") multi-dim arrays can perform pretty well - until 
> you start passing them around as function parameters.
> 
> Two ways to get around that would be to wrap the arrays with a UDT 
> passed byref, or use ptr params, with ptr's being much more intuitive 
> for most applications of static arrays (IMO).
> 
> Attached is a matrix multiplication program ported to D from the 
> original Shootout Delphi version (*).
> 
> The Delphi program has much cleaner syntax. For example, D pointer param 
> dereferencing would be (*m1)[a][b] = (*m2)[c][d] * (*m3)[e][f] .
> 
> For me this begs the question: Why aren't D static arrays passed byref 
> (**)?
> 
> (*) http://dada.perl.it/shootout/matrix_allsrc.html
> (**) static array params cannot be 'inout'.
> 
> Thanks,
> 
> - Dave
> 
> 
> ------------------------------------------------------------------------
> 
> module matrix;
> 
> import std.conv, std.stdio;
> 
> void main(char[][] args)
> {
>   int NUM = args.length > 1 ? toInt(args[1]) : 1;
>   TMatrix M1, M2, MM;
> 
>   mkmatrix(SIZE, SIZE, &M1);
>   mkmatrix(SIZE, SIZE, &M2);
>   for(int i = 0; i < NUM; i++)
>     mmult(SIZE, SIZE, &M1, &M2, &MM);
>   writefln(MM[0][0]," ",MM[2][3]," ",MM[3][2]," ",MM[4][4]);
> }
> 
> const SIZE = 30;
> 
> typedef int[SIZE][SIZE] TMatrix;
> 
> void mkmatrix(int rows, int cols, TMatrix* mx)
> {
>   int count = 1;
>   for(int R = 0; R < rows; R++)
>     for(int C = 0; C < cols; C++)
>     {
>       (*mx)[R][C] = count;
>       count++;
>     }
> }
> 
> void mmult(int rows, int cols, TMatrix* m1, TMatrix* m2, TMatrix* mm)
> {
>   for(int i = 0; i < rows; i++)
>     for(int j = 0; j < cols; j++)
>     {
>       int val = 0;
>       for(int k = 0; k < cols; k++)
>         val += (*m1)[i][k] * (*m2)[k][j];
>       (*mm)[i][j] = val;
>     }
> }