A bit better version:
http://codepad.org/jhbYxEgU
I think this code is good compared to the original (there are
better algorithms).
You can make it much faster even without really changing the
algorithm. Just by reversing the order of inner two loops like
this:
void matrixMult2(in int[][] m1, in int[][] m2, int[][] m3) pure
nothrow {
foreach (immutable i; 0 .. m1.length)
foreach (immutable k; 0 .. m2[0].length)
foreach (immutable j; 0 .. m3[0].length)
m3[i][j] += m1[i][k] * m2[k][j];
}
you can make the code much more cache friendly (because now you
aren't iterating any matrix by column in the inner loop) and also
allow the compiler to do auto vectorization. matrixMul2() takes
2.6 seconds on my machine and matrixMul()takes 72 seconds (both
compiled with gdmd -O -inline -release -noboundscheck -mavx).
This isn't really relevant to the comparison with C++ in this
thread, I just thought it may be useful for anyone writing matrix
code.
