in reply to Re: Re: Re: Re: should this backspace removal code be done better?
in thread should this backspace removal code be done better?

Not any more. This new smack is a lot faster by eliminating the alternation.

#!/usr/bin/perl -w

use Benchmark qw(cmpthese);
$s = "\bthis is an\b correct\b\b\b usage\b";

sub uk {
  $a = $s;
  $a =~ s[(?:[^\cH]\cH|^\cH)][]g while 1+index $a, chr(8);
  $a;
}

sub new1 {
  $a = $s;
  while ($a =~ s/(?:[^\cH]\cH|^\cH+)//g) {}
  $a;
}

sub smack {
  $a = $s;
  $a =~ s/^\cH+//;
  1 while ($a =~ s/[^\cH]\cH//g);
  $a;
}

cmpthese(-5,{uk=>\&uk,new1=>\&new1,smack=>\&smack});
$s x= 100;
cmpthese(-5,{uk=>\&uk,new1=>\&new1,smack=>\&smack});

Benchmark: running new1, smack, uk, each for at least 5 CPU seconds...
      new1:  6 wallclock secs ( 5.39 usr +  0.03 sys =  5.42 CPU) @ 11
+344.28/s (n=61486)
     smack:  6 wallclock secs ( 5.24 usr +  0.02 sys =  5.26 CPU) @ 36
+814.64/s (n=193645)
        uk:  4 wallclock secs ( 5.26 usr +  0.06 sys =  5.32 CPU) @ 13
+261.09/s (n=70549)
         Rate  new1    uk smack
new1  11344/s    --  -14%  -69%
uk    13261/s   17%    --  -64%
smack 36815/s  225%  178%    --
Benchmark: running new1, smack, uk, each for at least 5 CPU seconds...
      new1:  5 wallclock secs ( 5.22 usr +  0.05 sys =  5.27 CPU) @ 14
+0.04/s (n=738)
     smack:  6 wallclock secs ( 5.26 usr +  0.07 sys =  5.33 CPU) @ 87
+3.55/s (n=4656)
        uk:  5 wallclock secs ( 5.18 usr +  0.04 sys =  5.22 CPU) @ 17
+6.44/s (n=921)
       Rate  new1    uk smack
new1  140/s    --  -21%  -84%
uk    176/s   26%    --  -80%
smack 874/s  524%  395%    --

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Re: Re: Re: Re: Re: Re: should this backspace removal code be done better?
by antirice (Priest) on Oct 05, 2003 at 08:27 UTC

    Small problem. You may want to clear out the leading \b's after the while statement. Like many others on this thread, you've been bitten by the terminal's evaluation of \b.

    #!/usr/bin/perl -l

$s = "\bt\b\bhello";

sub smack {
  $a = $s;
  $a =~ s/^\cH+//;
  1 while ($a =~ s/[^\cH]\cH//g);
  $a;
}

sub othersmack {
  $a = $s;
  1 while ($a =~ s/[^\cH]\cH//g);
  $a =~ s/^\cH+//;
  $a;
}

print smack();
print othermack();

print "smack correct" unless grep {ord==ord"\b"} split//,smack();
print "othersmack correct" unless grep {ord==ord"\b"} split//,othersma
+ck();
__END__
output:
hello
hello
othersmack correct

    [download]

    However, getting rid of the alternation is a good bit quicker. =)

    antirice    
    The first rule of Perl club is - use Perl
    The     ith rule of Perl club is - follow rule i - 1 for i > 1

[reply]
[d/l]
      Hell yes!   It's over 4 times faster than even my attempt, with your repair making it correct.   Gratuitous benchmark below: 
                     Rate     smack    new1      uk  badkcams othersmack
smack         188/s        --    -96%    -97%      -97%       -99%
new1         5088/s     2607%      --     -8%      -23%       -86%
uk           5517/s     2835%      8%      --      -16%       -85%
badkcams     6594/s     3409%     30%     20%        --       -82%
othersmack  37394/s    19797%    635%    578%      467%         --
            
               Rate     smack    new1      uk  badkcams othersmack
smack        42.6/s        --    -23%    -29%      -43%       -93%
new1         54.9/s       29%      --     -8%      -27%       -91%
uk           59.6/s       40%      9%      --      -21%       -90%
badkcams     75.0/s       76%     37%     26%        --       -88%
othersmack    626/s     1372%   1040%    951%      735%         --
      (See shenme's scratchpad for oogly program)
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