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Re^2: High-speed Date Formatting

by hdb (Parson)
on Jul 12, 2013 at 08:58 UTC ( #1043913=note: print w/ replies, xml ) Need Help??


in reply to Re: High-speed Date Formatting
in thread *SOLVED* High-speed Date Formatting

Another small speed up can be achieved by replacing

my $leaps = int( ($y - 1970) / 4 + 0.5 ); (((($y-1970)*365 +$leaps+MONTHS->{$m}+($d-1))*24 +$H)*60 +$M)*60 + +$S;

with

(((int(($y-1970)*365.25-.5)+MONTHS->{$m}+$d)*24 +$H)*60 +$M)*60 +$S;

in my experiments between 5 to 10%. All other attempts using split and unpack are much slower. I found substr to be very fast:

sub str2epoch3 { (((int((substr($_[0],12,4)-1970)*365.25-.5)+ MONTHS->{substr($_[0],8,3)}+substr($_[0],5,2))*24 +substr($_[0],1 +7,2))*60 + substr($_[0],20,2))*60 +substr($_[0],23,2); }

about 60% faster than BrowserUk's code. I wonder whether there is something wrong...

Here is my full code:
use strict; use warnings; use Benchmark qw/cmpthese/; use constant MONTHS => { qw[ Jan 0 Feb 31 Mar 59 Apr 90 May 120 Jun 151 Jul 181 Aug 212 Sep 242 Oct 272 Nov 303 Dec 334 ] }; sub str2epoch { my( $d, $m, $y, $H, $M, $S ) = $_[0] =~ m[^.... (\d\d) (...) (\d\d\d\d) (\d\d):(\d\d):(\d\d)] or die "Bad format $_[0]"; my $leaps = int( ($y - 1970) / 4 + 0.5 ); (((($y-1970)*365 +$leaps+MONTHS->{$m}+($d-1))*24 +$H)*60 +$M)*60 + +$S; } sub str2epoch2 { my( $d, $m, $y, $H, $M, $S ) = $_[0] =~ m[^.... (\d\d) (...) (\d\d\d\d) (\d\d):(\d\d):(\d\d)] or die "Bad format $_[0]"; (((int(($y-1970)*365.25-.5)+MONTHS->{$m}+$d)*24 +$H)*60 +$M)*60 +$ +S; } sub str2epoch3 { (((int((substr($_[0],12,4)-1970)*365.25-.5)+ MONTHS->{substr($_[0],8,3)}+substr($_[0],5,2))*24 +substr($_[0] +,17,2))*60 + substr($_[0],20,2))*60 +substr($_[0],23,2); } my $str = 'Fri, 01 Mar 2013 01:21:14 +0000'; cmpthese( -3, {BrowserUK => sub { str2epoch ($str) }, BUK2 => sub { str2epoch2($str) }, substr => sub { str2epoch3($str) }, } ); </readmore>


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