Beefy Boxes and Bandwidth Generously Provided by pair Networks
Perl: the Markov chain saw
 
PerlMonks  

Re: Comparison by position and value

by sgifford (Prior)
on Jan 02, 2005 at 20:35 UTC ( #418812=note: print w/replies, xml ) Need Help??


in reply to Comparison by position and value

It's the need to check the same digit appearing in different places in the two strings that makes this hard to do with bitwise string operations. But the only reason that bitwise string operations are so fast is because you can avoid making all of those jumps into the Perl interpreter; you can hand it both the strings and an operation, let it groove along in C for awhile, then come back with an answer.

You can get the same effect with Inline::C.

With a simple substr-based implementation, a C version is nearly 4 times faster than a nearly identical Perl version:

Benchmark: timing 100000 iterations of csimple3, simple3... csimple3: 5 wallclock secs ( 4.43 usr + 0.00 sys = 4.43 CPU) @ 22573.36/s (n=100000) simple3: 19 wallclock secs (16.90 usr + 0.01 sys = 16.91 CPU) @ 5913.66/s (n=100000)
Here's the code I used:
#!/usr/bin/perl use Benchmark; use Inline C => 'DATA', VERSION => 0.0, NAME => 'SimpleTest', OPTIMIZE => '-O3'; Inline->init; sub simple3 { my($a,$b)=@_; my(@seen); return undef if (length($a) != length($b)); foreach my $i (0..length($a)) { my($ac,$bc)=(substr($a,$i,1),substr($b,$i,1)); if ($ac eq $bc) { ; # Do nothing } elsif ($ac eq '_') { return undef if (++$seen[$bc] > 1); } elsif ($bc eq '_') { return undef if (++$seen[$ac] > 1); } else { return undef } } 1; } my @tests = (qw/ _8__3__19 48____7__ _8__3__19 4_2___7__ _8__3__19 4_8___7__ __8_3__19 48____7__ __8_3__19 84____7__ _8__3__19 48_____7_ / ); sub run_tests { my($func,$verbose,@tests)=@_; my ($s1, $s2); while (defined($s1 = shift(@tests))) { $s2 = shift(@tests); my $result = $func->($s1, $s2); print "$s1\n$s2: ",$result?"compatible":"not compatible","\n" if ($verbose); } } run_tests(\&csimple3, 1, @tests); timethese(100_000, { simple3 => sub { run_tests(\&simple3, 0, @tests) }, csimple3 => sub { run_tests(\&csimple3, 0, @tests) }, }); __DATA__ __C__ int csimple3(const char *a, const char *b) { int i; int l; unsigned char seen[256]; memset(seen,0,256); if ((l=strlen(a)) != strlen(b)) return 0; for(i=0;i<l;i++) { if (a[i] == b[i]) { ; /* Do nothing */ } else if (a[i] == '_') { if (++seen[b[i]] > 1) return 0; } else if (b[i] == '_') { if (++seen[a[i]] > 1) return 0; } else return 0; } return 1; }

Log In?
Username:
Password:

What's my password?
Create A New User
Node Status?
node history
Node Type: note [id://418812]
help
Chatterbox?
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others studying the Monastery: (3)
As of 2020-10-31 19:27 GMT
Sections?
Information?
Find Nodes?
Leftovers?
    Voting Booth?
    My favourite web site is:












    Results (291 votes). Check out past polls.

    Notices?