From: "Uri Guttman"
Subject: Re: Help on String to array !
Date: Wed, 10 Mar 2010 02:51:42 -0500

>>>>> "j" == jis writes:

j> As said regex and unpack took longer time than substr.
j> I use Windows. The following are the time taken.

j> 1. Regex : @arr = $hex =~ /[[:xdigit:]]{2}/g; - To read 4Mb file
j> into an array it took 1min 7 seconds.
j> 2. Unpack : @arr = unpack("(C2)*",$hex); - To read 4Mb file into
j> an array it took 3min 26seconds.
j> 3. Substr: while ($val=substr( $hex, $offs, 2))
j> {
j> push @arr, $val;
j> $offs+=2;
j> } - To read 4Mb file into an array it took 11 seconds.


i am sorry, i can't believe it took on the order of minutes to read in a
file and convert from hex to binary. this is not possible on anything
but an abacus. given you haven't shown the complete script for each
version i have to assume your code is broken in some way. also there is
no way a substr loop would be faster than unpack or a regex. both of
those would spend all their time in perl's guts while the substr version
spends most of its time doing slow perl ops in a loop. i say this from
plenty of experience benchmarking perl code. you can easily write an
incorrect test of this so i must ask you to post complete working
programs that exhibit the slowness you claim. i will wager large amounts
of quatloos i can fix them so the substr will be outed as the slowest
one.

uri

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