Re^2: counting backward (optimize foreach reverse low .. high

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Re^3: counting backward (optimize foreach reverse low .. high by BrowserUk (Patriarch) on Mar 02, 2013 at 15:29 UTC
But you still had to create a huge array in order to benefit from the optimisation; which kinda negates the purpose. This: `perl -E"@a=1..1e9; for( reverse @a ) { print $_; <> }"` consumes 18GB (that's Gigabytes!) of memory Whereas this: `perl -E"for( -1e9..1 ) { print -$_; <> }"` iterates the same range and consumes only 1.8MB of ram. Four orders of magnitude more memory, or a minus sign. My choice is simple; how about yours? With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday' Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice.	[reply] [d/l] [select]
Re^4: counting backward (optimize foreach reverse low .. high by Anonymous Monk on Mar 02, 2013 at 15:39 UTC
Four orders of magnitude more memory, or a minus sign. My choice is simple; how about yours? I'll use minus sign until perl5-porter optimizes foreach reverse rangeop Or i'll use for;;;	[reply]
Re^5: counting backward (optimize foreach reverse low .. high by BrowserUk (Patriarch) on Mar 02, 2013 at 16:59 UTC
Or i'll use for;;; It's a shame you can't use the c-style for as a modifier: `cmpthese -1, { a=>q[ 1 for -1e6..0; ], b=>q[ for( my $i=1e6; $i; --$i ){ 1 } ] };; Rate b a b 14.0/s -- -26% a 19.0/s 35% --` [download] With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday' Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice.	[reply] [d/l]
Re^3: counting backward (optimize foreach reverse low .. high by LanX (Saint) on Mar 02, 2013 at 15:24 UTC
AFAIK `for( @f )` is optimized to act like an iterator without expanding and caching the list. But in `for(reverse @f )` there is no `for`-context which helps `reverse` to act differently. I'm to lazy for benchmarks (we had them before), but this was surely not fixed in 5.8.8 Cheers Rolf	[reply] [d/l] [select]
Re^4: counting backward (optimize foreach reverse low .. high by dave_the_m (Monsignor) on Mar 02, 2013 at 15:35 UTC
`for(reverse @f)` has been optimised not to expand the array since 5.10.0. Dave.	[reply] [d/l]
Re^5: counting backward (optimize foreach reverse low .. high by LanX (Saint) on Mar 02, 2013 at 15:52 UTC
Maybe it's optimized for reversing arrays but not for reversing ranges: I had to stop the second version because the swapping started to freeze my system: `lanx@nc10-ubuntu:~$ perl -e'for my $i ( 0 .. 1e8 ) { $x=-1; $x+=$i }; +print "$x\n"' 50000000 lanx@nc10-ubuntu:~$ perl -e'for my $i ( reverse 0 .. 1e8 ) { $x=-1; $ +x+=$i };print "$x\n"' ^C^C^C lanx@nc10-ubuntu:~$ perl -version This is perl, v5.10.0 built for i486-linux-gnu-thread-multi ...` [download] Reversing ranges was what BUK did, but AnoMonk replied with a reference to a fix for reversing arrays! Cheers Rolf	[reply] [d/l]
Re^6: counting backward (optimize foreach reverse low .. high by dave_the_m (Monsignor) on Mar 02, 2013 at 17:37 UTC
Re^6: counting backward (optimize foreach reverse low .. high by Anonymous Monk on Mar 02, 2013 at 16:24 UTC
Re^5: counting backward (optimize foreach reverse low .. high by ikegami (Patriarch) on Mar 02, 2013 at 20:46 UTC
See Re^3: Mutable foreach list? (types of for) and Re^6: C-style for loop for a little more on the "for" optimisations.	[reply]
Re^4: counting backward (optimize foreach reverse low .. high by Anonymous Monk on Mar 02, 2013 at 15:30 UTC
You're wrong	[reply]
Re^5: counting backward (optimize foreach reverse low .. high by LanX (Saint) on Mar 02, 2013 at 15:56 UTC
you too! Cheers Rolf	[reply]
Re^6: counting backward (optimize foreach reverse low .. high by Anonymous Monk on Mar 02, 2013 at 16:19 UTC
Re^6: counting backward (optimize foreach reverse low .. high by Anonymous Monk on Mar 02, 2013 at 16:21 UTC