I can give you an example program that analyses
C++ code. It has as input a tags file and a bunch
of C++ code. And it generates a bunch of html files
showing the class hierachy and the complexity off all classes. It does this in three steps:
- It parses the tagsfile to figure out
where to find all the classes and operations in the code,
and to build the class tree. This uses a fair amount
of regular expressions and a couple of functions that recursively walks through a hashes and arrays.
- It scans the c++ source files to figure out how many lines of code there are per operation and class.
The results are later used to sort the classes according
to complexity.
- It transforms the results into html files.
The code has not been optimized, and I think there
probably plenty of stuff to optimize. It has about 20 subs.
It was written when I just started programming in Perl,
so it probably can also be used to show how to improve
style and programming techniques.
You would need to have a fair amount of C++ code to analyse
and access to a ctags program. In addition, the C++ code should not use any namespaces.
Have Fun
| [reply] |
Just some slight, stupid optimizations to save the slightest bit of space.
- substr before regex (if possible). transliteration before regex. Use regex as last resort.
- use single quotes if no interpolation is needed (REALLY minor optimization).
- $foo ? $bar; is faster than $bar if $foo; which is faster than if($foo){$bar}.
- require is always faster than use.
- use Memoize if that slow function that is called a couple times needs speeding up.
Tiptoeing up to a Perl hacker.
Dave AKA damian
| [reply]
[d/l]
[select] |
I will be very interested in the outcome of such a study. We are in the process right at this moment profiling some data loading code that takes about 1/2 hour to run on some very beefy hardware (Sun Sparc 4500, 2 gig memory, etc...).
One of the things we are looking at is de-referencing. Assume you have a hash reference that is a complex data structure:
my $href = {
'x' => {
'y' => {
'z' => [ $xref, $yref, $zref ],
},
'strange' => { ..... },
},
'charm' => { .... },
};
Now imagine that the example above is actually a reference to an enormous object, with grand-children, great-grand-children, and great-great-great-great-grandchildren. From what I can see, every time you de-reference some or all of the object, a copy is made.
foreach my $obj (%{$href})
# This dereference ^ causes a deep copy to be made
In the case where these are really big objects, as some of ours are, that would be rather rough, especially if we iterate through children, then grand-children, then deeper still.
At this point, the savings gained by passing a reference to a function is lost due to the fact that a copy of the referent is made in the function. For instance:
01: my $list = [1, 2, 3];
02: doStuff($list);
03:
04: sub doStuff
05: {
06: my $listRef = shift;
07: foreach $listElement (@{$listRef})
08: {
09: print "$listElement \n";
10: }
11: }
In line 7, a deep copy of the list is made. If we change the sub to take not a reference, but the whole list, is this equivalent, or is it different?
Of course, if in the subroutine you de-reference the thing more than once, you could be incurring huge overhead. This is not at all an issue with a puny example like the above, but we have rather hierarchical data, with objects that contain child objects, with children, etc. All method calls are by reference, and most references are de-referenced all over the place.
I can't send you our code (proprietary, you know) but I might be able to put together a better example to show you what I mean. Right now, one of our guys is looking in to this. I will publish the results of our study here.
Brian - a.k.a. DrSax
| [reply]
[d/l]
[select] |
Copies are not being made where you think they are.
| [reply] |
foreach my $obj (%{$href})
# This dereference ^ causes a deep copy to be made
actually, this is more accurate:
foreach my $obj (%{$href})
#here ^ is the copy
If you check the ref()-iness of $obj, you'll find that there isn't any at all. The appropriate value is copied into $obj on each run of the loop. I'm not at all sure what it is you're trying to solve with this, but if you need access to the key/value pair without the big, horrendous copy, maybe something like this:
foreach my $key (keys %{$href})
{
#do what you need with $key and $href->{$key}
}
Hope you find this useful!
~Cybercosis
nemo accipere quod non merere | [reply]
[d/l]
[select] |
for and foreach make the argument an alias to (not a copy of) the values in the list.
Even if you copy a reference, you still get a reference, so I don't understand what you are trying to say.
my $href = {
'x' => {
'y' => {
'z' => [ $xref, $yref, $zref ],
},
#'strange' => { ..... },
},
#'charm' => { .... },
};
for my $obj ( %$href ) {
print "$obj: ",ref($obj),$/;
my $copy= $obj;
print "$copy: ",ref($copy),$/;
}
__END__
prints:
x:
x:
HASH(0x1a65030): HASH
HASH(0x1a65030): HASH
-
tye
(but my friends call me "Tye") | [reply]
[d/l] |
