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NPathComplexity: extend documentation to make clear how it works. #1218

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Roman Ivanov 2015-06-18 00:00:56 -07:00
parent a66bed035b
commit da1921b4d0
1 changed files with 59 additions and 4 deletions
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src/xdocs/config_metrics.xml
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@ -416,13 +416,68 @@ class CC {
paths through a function. It takes into account the nesting of
conditional statements and multi-part boolean expressions
(e.g., A && B, C || D, etc.).
<br/>
The NPATH metric was designed base on Cyclomatic complexity to
avoid problem of Cyclomatic complexity metric like nesting level within a function.
</p>
<p>
Metic wsa described at <a href="http://dl.acm.org/citation.cfm?id=42379">"NPATH: a measure of execution path complexity and its applications"</a>. If you need detaled description of algorithm, please read that article,
it well written and have number of examples and details.
</p>
<p>Here is some quotes:</p>
<blockquote>An NPATH threshold value of 200 has been established
for a function. The value 200 is based on studies done
at AT&amp;T Bell Laboratories [1988 year].
</blockquote>
<blockquote>
Some of the most effective methods of reducing the NPATH value include<br/>
- distributing functionality,<br/>
- implementing multiple if statements as a switch statement<br/>
- creating a separate function for logical expressions with a high count of and (&amp;&amp;) and or (||) operators.
</blockquote>
<blockquote>
Although strategies to reduce the NPATH complexity
of functions are important, care must be taken not to
distort the logical clarity of the software by applying a
strategy to reduce the complexity of functions. That is,
there is a point of diminishing return beyond which a
further attempt at reduction of complexity distorts the
logical clarity of the system structure.
</blockquote>
<table>
<thead><tr><th>Structure</th><th> Complexity expression </th></tr></thead>
<tr><td>if</td><td>NP((if-range))+NP((expr))+1</td></tr>
<tr><td>if-else</td><td>NP((if-range))+NP((else-range))+NP((expr))</td></tr>
<tr><td>while</td><td>NP((while-range))+NP((expr))+1</td></tr>
<tr><td>do while</td><td>NP((do-range))+NP((expr))+1</td></tr>
<tr><td>for</td><td>NP((for-range))+NP((exprl))+NP((expr2))+NP((expr3))+1</td></tr>
<tr><td>switch</td><td>NP((expr))+ S(i=1:i=n)NP((case-range(i)))+ NP((default-range))</td></tr>
<tr><td>?</td><td>NP((exprl))+NP((expr2))+NP((expr3))+2</td></tr>
<tr><td>goto label</td><td>1</td></tr>
<tr><td>break</td><td>1</td></tr>
<tr><td>Expressions</td><td>Number of &amp;&amp; and || operators in expression</td></tr>
<tr><td>continue</td><td>1</td></tr>
<tr><td>return</td><td>1</td></tr>
<tr><td>sequential</td><td>1</td></tr>
<tr><td>Function call</td><td>1</td></tr>
<tr><td>C function</td><td>P(i=1:i=N) NP(Statement(i))</td></tr>
</table>
<p>
Rationale: Nejmeh says that his group had an informal NPATH
<b>Rationale:</b> Nejmeh says that his group had an informal NPATH
limit of 200 on individual routines; functions that exceeded
this value were candidates for further decomposition - or at
least a closer look.
least a closer look.
<b>Please do not be fanatic with limit 200</b>
- choose number that suites your project style. Limit 200 is
empirical number base on some sources of at AT&amp;T Bell Laboratories
of 1988 year.
</p>
</subsection>
@ -452,11 +507,11 @@ class CC {
</source>
<p>
To configure the check with a threshold of 20:
To configure the check with a threshold of 1000:
</p>
<source>
&lt;module name=&quot;NPathComplexity&quot;&gt;
&lt;property name=&quot;max&quot; value=&quot;20&quot;/&gt;
&lt;property name=&quot;max&quot; value=&quot;1000&quot;/&gt;
&lt;/module&gt;
</source>
</subsection>