Re^2: Summing Up Array Elements By Group

Even faster:

tin4=> sub {
  my $b = 0;
  $output[$_] = $arr[$b++] + $arr[$b++] + $arr[$b++]
    for 0..@arr/3;
},
tin5=> sub {
  my $b = -1;
  $output[$_] = $arr[++$b] + $arr[++$b] + $arr[++$b]
    for 0..@arr/3;
},
[download]

       Rate tin1 tin2 tin3 tin4 tin5
tin1 10.2/s   -- -54% -59% -65% -68%
tin2 22.2/s 118%   --  -9% -23% -30%
tin3 24.5/s 141%  10%   -- -15% -23%
tin4 28.8/s 183%  30%  17%   --  -9%
tin5 31.7/s 211%  43%  29%  10%   --
[download]

Comment on Re^2: Summing Up Array Elements By Group Select or Download Code

Replies are listed 'Best First'.
Re^3: Summing Up Array Elements By Group by hbm (Hermit) on Jan 21, 2009 at 18:34 UTC
ikegami, this one knocks me down! Did you know in advance that `++$b` would be faster than `$b++`? Do you know why that is?	[reply]
Re^4: Summing Up Array Elements By Group by gwadej (Chaplain) on Jan 21, 2009 at 18:55 UTC
`$b++` makes a copy so that it can return the previous value. `++$b` does not need to. I have run into this issue before in C++, but it was normally not a problem for integers. Scalars on the other hand are a different beast. G. Wade	[reply] [d/l] [select]
Re^5: Summing Up Array Elements By Group by ikegami (Patriarch) on Jan 21, 2009 at 19:39 UTC
it was normally not a problem for integers. I find it odd that it would matter at all for ints. `++a --- inc a mov a, reg a++ --- mov a, reg inc a` [download]	[reply] [d/l]
Re^6: Summing Up Array Elements By Group by gwadej (Chaplain) on Jan 21, 2009 at 20:32 UTC
Re^4: Summing Up Array Elements By Group by ikegami (Patriarch) on Jan 21, 2009 at 18:57 UTC
`$b++` needs to create a new anonymous scalar because the result is different than the $b. `++$b` just returns a pointer to `$b`. `$ perl -le'my $b = 4; $r = \( $b++ ); $$r = 20; print $b' 5 $ perl -le'my $b = 4; $r = \( ++$b ); $$r = 20; print $b' 20` [download]	[reply] [d/l] [select]
Re^5: Summing Up Array Elements By Group by hbm (Hermit) on Jan 21, 2009 at 19:06 UTC
Nice! One point for your original and another for gwadej's explanation.	[reply]