qr// operator to pre-compile your regexps. It often is the easiest way to write regexp components to build up more complex regexps. Using it to build your regexps once is a good idea. But don't screw up (like parrot's assemble.pl did) by telling perl to recompile the same regexp every time you enter a subroutine: sub foo {
my $reg1 = qr/.../;
my $reg2 = qr/... $reg1 .../;You should pull those two regexp definitions out of the subroutine into package variables, or file scoped lexicals.
You find what is slow by using a profiler. People often guess where they think their program is slow, and get it hopelessly wrong. Use a profiler.
Devel::DProf is in the perl core from version 5.6. If you're using an earlier perl you can get it from CPAN.
You run your program with -d:DProf
perl5.8.0 -d:DProf enc2xs.orig -Q -O -o /dev/null ...
which times things and stores the data in a file named tmon.out. Then you run dprofpp to process the tmon.out file, and produce meaningful summary information. This excerpt is the default length and format, but you can use options to change things - see the man page. It also seems to show up a minor bug in dprofpp, because it manages to total things up to get 106%. While that's not right, it doesn't affect the explanation.
Total Elapsed Time = 66.85123 Seconds
User System Time = 62.35543 Seconds
Exclusive Times
%Time ExclSec CumulS #Calls sec/call Csec/c Name
106. 66.70 102.59 218881 0.0003 0.0005 main::enter
49.5 30.86 91.767 6 5.1443 15.294 main::compile_ucm
19.2 12.01 8.333 45242 0.0003 0.0002 main::encode_U
4.74 2.953 1.078 45242 0.0001 0.0000 utf8::unicode_to_native
4.16 2.595 0.718 45242 0.0001 0.0000 utf8::encode
0.09 0.055 0.054 5 0.0109 0.0108 main::BEGIN
0.01 0.008 0.008 1 0.0078 0.0078 Getopt::Std::getopts
0.00 0.000 -0.000 1 0.0000 - Exporter::import
0.00 0.000 -0.000 3 0.0000 - strict::bits
0.00 0.000 -0.000 1 0.0000 - strict::import
0.00 0.000 -0.000 2 0.0000 - strict::unimportAt the top of the list, the subroutine enter takes about half the total CPU time, with 200,000 calls, each very fast. That makes it a good candidate to optimise, because all you have to do is make a slight change that gives a small speedup, and that gain will be magnified 200,000 times. [It turned out that enter was tail recursive, and part of the speed gain I got was by making it loop instead]
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