↑ include |
}'
time perl -Mstrict -we 'my ; for( 0..999_999 ) { }'
when run on different variants of code you can think of, can give surprising
results. Even small modifications can matter a lot. Be careful not to
"measure" code that can get optimized away, because you discard the result, or
because it depends on constants.
Depending on your system, this will tell you in kb how fat Perl got:
perl -Mstrict -we '; system "ps -ovsz $$"'
Below we only show the code within the C<-e> option as one liners.
=back
=head2 Regexps
=over
=item Use simple regexps
Several matches combined with C<||> are faster than a big one with C<|>.
=item Use precompiled regexps
Instead of interpolating strings into regexps (except if the string will never
change and you use the C modifier), precompile the regexp with C function, where this doesn't
work reliably. There a hex form is still a fair bit faster than default
strings. Actually this can even be faster than stringified int, depending on
the version or maybe configuration of perl. As of 5.8.1 there is also the
equivalent but hopefully reliable Scalar::Util::refaddr
my @list = map { bless { $_ => 1 }, "someclass" } 0..9; my( %a, %b );
timethis -10, sub { $a{$_} = 1 for @list };
timethis -10, sub { $b{int()} = 1 for @list };
timethis -10, sub { $b{sprintf '%x', $_} = 1 for @list };
timethis -10, sub { $b{refaddr $_} = 1 for @list };
There is also sprintf '%p' which supposedly outputs a pointer, but depending
on which expression leads to the same ref, you get different values, so it's
useless.
=item Beware of strings
Perl is awful for always copying strings around, even if you're never going to
modify them. This wastes CPU and memory. Try to avoid that wherever
reasonably possible. If the string is a function parameter and the function
has a modest length, don't copy the string into a C variable, access it
with C<$_[0]> and document the function well. Elsewhere, the aliasing feature
of C can help. Or just use references to strings, which are fast
to copy. If you somehow ensure that same strings get stored only once, you
can do numerical comparison for equality.
=item Avoid bit operations
If you have disjoint bit patterns you can add them instead of or`ing them.
Shifting can be performed my multiplication or integer division. Retaining
only the lowest bits can be achieved with modulo.
Separate boolean hash members are faster than stuffing everything into an
integer with bit operations or into a string with C.
=item Use order of boolean operations
If you only care whether an expression is true or false, check the cheap
things, like boolean variables, first, and call functions last.
=item Use undef instead of 0
It takes up a few percent less memory, at least as hash or list values. You
can still query it as a boolean.
my %x; $x{$_} = 0 for 0..999_999; system "ps -ovsz $$"
my %x; undef $x{$_} for 0..999_999; system "ps -ovsz $$"
my @x = (0) x 999_999; system "ps -ovsz $$"
my @x = (undef) x 999_999; system "ps -ovsz $$"
=item Choose for or map
These are definitely not equivalent. Depending on your use (i.e. the list and
the complexity of your code), one or the other may be faster.
my @l = 0..99;
for( 0..99_999 ) { map $a = " $_ ", @l }
for( 0..99_999 ) { map $a = " $_ ", 0..99 }
for( 0..99_999 ) { $a = " $_ " for @l }
for( 0..99_999 ) { $a = " $_ " for 0..99 }
=item Don't alias $_
While it is convenient, it is rather expensive, even copying reasonable
strings is faster. The last example is twice as fast as the first "for".
my $x = "abcdefg"; my $b = 0;
for( "$x" ) { $b = 1 - $b if /g/ } # Copy needed only if modifying.
for( $x ) { $b = 1 - $b if /g/ }
local *_ = \$x; $b = 1 - $b if /g/;
local $_ = $x; $b = 1 - $b if /g/; # Copy cheaper than alias.
my $y = $x; $b = 1 - $b if $y =~ /g/;
=back
=head1 AUTHOR
Daniel Pfeiffer
makepp-2.0.98.3/pod/makeppreplay.pod 0000644 0001750 0001750 00000016602 12067152515 017357 0 ustar pfeiffer pfeiffer =head1 NAME
makeppreplay -- Fast repeater of selected makepp actions
=for vc $Id: makeppreplay.pod,v 1.11 2012/12/27 23:10:05 pfeiffer Exp $
=head1 DESCRIPTION
=for genindex '[-$][-?\w]+' makeppreplay.pod
BEL<-?|/_>,E
BEL<-A|/a_filename>,
L<--args-file|/a_filename>,
L<--arguments-file|/a_filename>,E
BEL<-C|/c_directory>,
L<-c|/c>,E
BEL<--directory|/c_directory>,
L<--dry-run|/n>,E
BEL<-h|/_>,
L<--help|/_>,E
BEL<-I|/i_directory>,
L<--include|/i_directory>,
L<--include-dir|/i_directory>,E
BEL<--just-print|/n>,E
BEL<-k|/k>,
L<--keep-going|/k>,E
BEL<--log|/log_logfilename>,
L<--log-file|/log_logfilename>,E
BEL<-M|/m_module_arg>,
L<$MAKEPPREPLAYFLAGS|/_makeppreplayflags>,
L<--module|/m_module_arg>,E
BEL<-n|/n>,
L<--no-log|/no_log>,
L<--no-print-directory|/no_print_directory>,
L<--no-warn|/no_warn>,E
BEL<--profile|/profile>,E
BEL<--recon|/n>,
L<--root-dir|/c>,
L<--root-directory|/c>,E
BEL<-s|/s_perl_expression>,
L<--sed|/s_perl_expression>,E
BEL<-t|/t>,
L<--temporary|/t>,E
BEL<-V|/v>,
L<--version|/v>
B S<[ I