Re: How to avoid using the slow array subscripting operator?

[Xi Liu]

I know I am doing the repetitive and useless summing again and again. What
confuses me is that using the same algorithm, I mean

 for my $i (99 .. 60000)
{
      my $sum;
      map {$sum += $_->{foo_value}} @lines[$i - $n + 1 .. $i];
      push @res, $sum;
}

in perl and

for(int i =99; i <= 60000; i++)
{
      int sum = 0;
      for(int j = i - n +1; j < i;  j++)
          sum += lines[$j].foo_value;
      res[i] = sum;
}

in c, there is a huge difference in efficiency.
the c program,  even using the same stupid algorithm, the cost of time is
acceptable. So I translated it to perl , and avoid the slow subscripting
operations using map on sliced array, I suppose the perl program would be
slower, but I don't predict such a huge difference, you don't even need a
benchmark or profiling tool to notice the efficiency difference. This is
what I am confused.
Thanks for your patience!