(Note this is cross posted on perlmonks as well)
So I was reading the Cylcomatic Complexity thread on perl monks, and it occured to me that B::Concise actually gives up some of the necessary information (at least I think it does).
Given this code:
print "Hello World";
I got this output:
stevan% perl -MO=Concise test.pl 6 <@> leave[1 ref] vKP/REFC ->(end) 1 <0> enter ->2 2 <;> nextstate(main 1 test.pl:3) v ->3 5 <@> print vK ->6 3 <0> pushmark s ->4 4 <$> const[PV "Hello World"] s ->5
Now I freely admit that both my understanding of Cylcomatic Complexity and B::Concise's output are most likely radically flawed, but I am going to ramble a bit here anyway.
Using this definition for CC (Cylcomatic Complexity)
Cyclomatic complexity may be considered a broad measure of soundness and
confidence for a program. Introduced by Thomas McCabe in 1976, it measures
the number of linearly-independent paths through a program module.
And with this (flimsy) interpretation of the B::Concise output:
(opcode-sequence-number) <0> (opcode_name) -> (next-opcode-sequence-number)
It seems to me that our code could be viewed as the following graph:
1 -> 2
2 -> 3
3 -> 4
4 -> 5
5 -> 6
6 -> (end)Simple right? Since there is only one "linearly-independent path" the CC-metric for this might be 1.
Now let's take a look at a slightly more complex bit of code:
if (shift) {
print "Hello World";
}
else {
print "Goodbye World";
}And here is the B::Concise output:
a <@> leave[1 ref] vKP/REFC ->(end) 1 <0> enter ->2 2 <;> nextstate(main 4 test.pl:3) v ->3 - <1> null vK/1 ->a 6 <|> cond_expr(other->7) vK/1 ->b 5 <1> shift sK/1 ->6 4 <1> rv2av[t2] sKRM/1 ->5 3 <#> gv[*ARGV] s ->4 - <@> scope vK ->- - <0> ex-nextstate v ->7 9 <@> print vK ->a 7 <0> pushmark s ->8 8 <$> const[PV "Hello World"] s ->9 g <@> leave vKP ->a b <0> enter v ->c c <;> nextstate(main 2 test.pl:7) v ->d f <@> print vK ->g d <0> pushmark s ->e e <$> const[PV "Goodbye World"] s ->f
Now here is the 2 graphs for this:
1 -> 2
2 -> 3
3 -> 4
4 -> 5
5 -> 6
6 -> 7 (<<< conditional here)
7 -> 8
8 -> 9
9 -> (end)and:
1 -> 2
2 -> 3
3 -> 4
4 -> 5
5 -> 6
6 -> b (<<< conditional here)
b -> c
c -> d
d -> e
e -> f
f -> g
g -> (end)We now have two "linearly-independent path" the CC-metric for this might be 2.
It seems to get a little tricky when we have subroutines, here is some code:
sub start {
print test();
return "Goodbye World";
} sub test {
return "Hello world"
}print start();
And here is the B::Concise output (notice we need to pass the sub-names to get them to output):
perl -MO=Concise,-main,start,test test.pl main::start: b <1> leavesub[1 ref] K/REFC,1 ->(end) - <@> lineseq KP ->b 1 <;> nextstate(main 1 test.pl:5) v ->2 6 <@> print vK ->7 2 <0> pushmark s ->3 5 <1> entersub[t2] lKS/TARG,1 ->6 - <1> ex-list lK ->5 3 <0> pushmark s ->4 - <1> ex-rv2cv sK/1 ->- 4 <#> gv[*test] s/EARLYCV ->5 7 <;> nextstate(main 1 test.pl:6) v ->8 a <@> return K ->b 8 <0> pushmark s ->9 9 <$> const[PV "Goodbye World"] s ->a main::test: g <1> leavesub[1 ref] K/REFC,1 ->(end) - <@> lineseq KP ->g c <;> nextstate(main 2 test.pl:10) v ->d f <@> return K ->g d <0> pushmark s ->e e <$> const[PV "Hello world"] s ->f main program: o <@> leave[1 ref] vKP/REFC ->(end) h <0> enter ->i i <;> nextstate(main 3 test.pl:14) v ->j n <@> print vK ->o j <0> pushmark s ->k m <1> entersub[t2] lKS/TARG,1 ->n - <1> ex-list lK ->m k <0> pushmark s ->l - <1> ex-rv2cv sK/1 ->- l <#> gv[*start] s ->m
If we look at the "main program:" label as a starting place:
h -> i
i -> j
j -> k
k -> l
l -> *start (
1 -> 2
2 -> 3
3 -> 4
4 -> *test (
c -> d
d -> e
e -> f
f -> g (return)
) -> 5
6 -> 7
7 -> 8
8 -> 9
9 -> a
a -> b (return)
) -> m
m -> n
n -> o
0 -> (end)We now only have one "linearly-independent path" so the CC-metric for this would be 1.
Now of course there are some issues with this. To start with B::Concise's sequence numbers are in base 36 and values greater than 62 are not supported according to the docs. However, if you use the B::Concise functional interface, it seems that is might be possible to get around this restriction by using the perl opcode hex addresses instead of the sequence numbers. However now I am getting into needing to really write some code, and I am currently out of time and need to get back to "real" work. But anyway I am interested in comments from the group.
Steve
On Dec 8, 2004, at 8:27 AM, Rob Kinyon wrote:
http://www.perlmonks.org/?node_id=413087 has a discussion of Cylcomatic Complexity, which seems to be exactly what we're trying to do here ...
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