Hello
I wrote 2 almost identical test programs(matrix multiplication). One on C and another on D. And D prorgram was 15 times slower!
Was it my mistake or not?
Thank you

p.s. code:
void test (int n) {
  float[] xs = new float[n*n];
  float[] ys = new float[n*n];
  for(int i = n-1; i>=0; --i) {
    xs[i] = 1.0;
  }
 for(int i = n-1; i>=0; --i) {
    ys[i] = 2.0;
  }
  float[] zs = new float[n*n];
  for (int i=0; i<n; ++i) {
    for (int j=0; j<n; ++j) {
      float s = 0.0;
      for (int k=0; k<n; ++k) {
        s = s + (xs[k + (i*n)] * ys[j + (k*n)]);
      }
      zs[j+ (i*n)] =  s;
    }
  }
  delete xs;
  delete ys;
  delete zs;
}

baleog wrote:
> Hello
> I wrote 2 almost identical test programs(matrix multiplication). One on C and another on D. And D prorgram was 15 times slower! Was it my mistake or not?
> Thank you
> 
> p.s. code:
> void test (int n) {    float[] xs = new float[n*n];
>   float[] ys = new float[n*n];
>   for(int i = n-1; i>=0; --i) {
>     xs[i] = 1.0;
>   }
>  for(int i = n-1; i>=0; --i) {
>     ys[i] = 2.0;
>   }
>   float[] zs = new float[n*n];
>   for (int i=0; i<n; ++i) {
>     for (int j=0; j<n; ++j) {
>       float s = 0.0;
>       for (int k=0; k<n; ++k) {
>         s = s + (xs[k + (i*n)] * ys[j + (k*n)]);
>       }
>       zs[j+ (i*n)] =  s;
>     }
>   }
>   delete xs;
>   delete ys;
>   delete zs;
> }
> 


To me your code looks reasonable, although you probably want to take the startup time and the gc out of the equation since that cost is fixed. BTW: here's a slightly more optimal reverse loop:

for(int i = n; --i>0; )

-Joel

On Sat, 14 Jun 2008 11:34:20 -0700, janderson wrote:

>...To me your code looks reasonable, although you probably want to take
the
> startup time and the gc out of the equation since that cost is fixed. BTW: here's a slightly more optimal reverse loop:
> 
> for(int i = n; --i>0; )
> 
> -Joel

wouldn't that be:
for(int i = n; i-- >0; )
?
first time through i == n-1, last time through i == 0.

Charles Hixson wrote:
> On Sat, 14 Jun 2008 11:34:20 -0700, janderson wrote:
> 
>> ...To me your code looks reasonable, although you probably want to take 
> the
>> startup time and the gc out of the equation since that cost is fixed.
>> BTW: here's a slightly more optimal reverse loop:
>>
>> for(int i = n; --i>0; )
>>
>> -Joel
> 
> wouldn't that be:
> for(int i = n; i-- >0; )
> ?
> first time through i == n-1, last time through i == 0.

Actually it should be:

for(int i = n; --i>=0; )

(missed the >=)

-Joel