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<p>We&#8217;ve mentioned in the past that the code we write isn&#8217;t maintaining heartbeats or being used in life-critical settings, but what if your code is?  NASA happens to be a company who has code that is life and mission critical and it&#8217;s very possible it won&#8217;t even be accessible once it leaves earth.  In this episode, we explore what has been deemed &#8220;The Power of 10&#8221; for writing safety-critical code.  </p>



<p>If you&#8217;re listening on a podcast player and would like to see all the show notes, head to:<a href="https://www.codingblocks.net/episode219">https://www.codingblocks.net/episode219</a></p>



<span id="more-41105"></span>



<h2 class="wp-block-heading" id="nasas-power-of-ten">NASA&#8217;s Power of Ten</h2>



<p>Their rules to ease the use of static analysis</p>



<h3 class="wp-block-heading" id="rule-1-simple-control-flow">Rule #1 Simple Control Flow</h3>



<ul>
<li>You&#8217;re not allowed to use:
<ul>
<li>goto</li>



<li>setjmp</li>



<li>longjmp</li>



<li>recursion</li>
</ul>
</li>
</ul>



<h3 class="wp-block-heading" id="rule-2-limit-all-loops-to-a-fixed-upper-bound">Rule #2 Limit all loops to a fixed upper bound</h3>



<ul>
<li>For example, linked list traversals include checking against some maximum iteration boundary, and the boundary is always an integer.</li>



<li><em>&#8220;If a tool cannot prove the loop bound statically, the rule is considered violated.&#8221;</em></li>
</ul>



<h3 class="wp-block-heading" id="rule-3-do-not-use-the-heap">Rule #3 Do not use the heap</h3>



<ul>
<li>So no need for malloc and free.</li>



<li>Rely soly on the use of stack memory instead.</li>



<li>This is because quite a few memory bugs are due to the use of the heap and garbage collectors. Things like:
<ul>
<li>memory leaks</li>



<li>use-after-free</li>



<li>heap overflows</li>



<li>heap exhaustion</li>
</ul>
</li>



<li>Applications that make use of the heap cannot be proven by a static analyzer.</li>



<li>By only using stack memory, including upper boundaries where necessary, you can commute exactly the most amount of memory your application will need.</li>



<li>And bonus, by only using the stack, you the eliminate the possibility of the previously mentioned memory bugs.</li>
</ul>



<h3 class="wp-block-heading" id="rule-4-function-sizes-are-limited">Rule #4 Function sizes are limited</h3>



<ul>
<li>Functions should only do one thing but might require multiple steps.
<ul>
<li>Very consistent with Uncle Bob&#8217;s series and other best practice principles.</li>
</ul>
</li>



<li>NASA recommends that functions be limited to 60 lines or what can fit on a single printed page.</li>



<li>This makes it easier for someone reviewing your code to read and understand that function in it&#8217;s entirety.</li>



<li>This limitation also helps to make sure that your function is testable, i.e. it&#8217;s not just some meandering 2,000 line long function with 18 levels of nesting.</li>
</ul>



<h3 class="wp-block-heading" id="rule-5-hide-your-data">Rule #5 Hide your data</h3>



<ul>
<li><code>"Data hiding is a technique of hiding internal object details. Data hiding restricts the data access to class members. It maintains data integrity."</code></li>



<li>The idea here is to declare variables as close as possible to where they are used at the lowest possible scope.
<ul>
<li>Meaning, rather than declare some variable that you only need inside of a loop at the function level, instead, declare that same variable inside the loop.</li>
</ul>
</li>



<li>Doing this accomplishes two things:
<ul>
<li>First, it reduces the amount of code that can access those variables, and more importantly, you &#8230;</li>



<li>Second, reduce the number of touch points that might change a variable&#8217;s value which aides debugging efforts when you want to understand why it got some unexpected value.</li>
</ul>
</li>
</ul>



<h3 class="wp-block-heading" id="rule-6-check-the--return-values">Rule #6 Check the $#*!#**#@ return values</h3>



<ul>
<li>How many times have you been bitten by code that made some call, even shell scripts/commands, where the call failed, but the return value that would have saved you wasn&#8217;t checked?</li>



<li>Check the return values of everything that returns something.
<ul>
<li>Always check them</li>



<li><strong><em>All of them</em></strong></li>
</ul>
</li>



<li>If you explicitly want to ignore a return value, such as when printing to the screen, you are to explicitly cast the return to void so that a reviewer knows that you do not care about that particular return value.</li>



<li>Failure to check a return value or cast it to void will be brought up in a code review.</li>
</ul>



<h3 class="wp-block-heading" id="rule-7-use-of-the-preprocessor-is-very-limited">Rule #7 Use of the Preprocessor is very limited</h3>



<ul>
<li>NASA limits the use of the C preprocessor to only file inclusions and very simple macros.</li>



<li><em>&#8220;The C preprocessor is a powerful obfuscation tool that can destroy code clarity and befuddle many text-based checkers.&#8221;</em></li>



<li>Specifically, conditionals that can change the code at compile time are called out by the Power of 10</li>



<li>For example, if you have 10 different flags that can be changed at compile time, you have 2^10 build targets that need to be tested.
<ul>
<li>In other words, preprocessor conditionals can exponentially increase your testing requirements.</li>
</ul>
</li>
</ul>



<h3 class="wp-block-heading" id="rule-8-pointer-use-is-restricted">Rule #8 Pointer use is restricted</h3>



<ul>
<li><em>&#8220;No more than one level of dereferencing should be used. Dereference operations may not be hidden in macro definitions or inside typedef declarations.&#8221;</em>
<ul>
<li><a href="https://www.tutorialspoint.com/what-does-dereferencing-a-pointer-mean-in-c-cplusplus">https://www.tutorialspoint.com/what-does-dereferencing-a-pointer-mean-in-c-cplusplus</a></li>
</ul>
</li>



<li>This is because pointers, albeit powerful, are easy to misuse.</li>



<li>Doing this limits you to structures that more properly track your pointers.</li>



<li>Pointer restrictions also include not using function pointers.
<ul>
<li>This is because function pointers obfuscate the control flow of your application.</li>



<li>They also make it more difficult to statically analysis your code.</li>
</ul>
</li>
</ul>



<h3 class="wp-block-heading" id="rule-9-compile-in-pedantic-mode">Rule #9 Compile in Pedantic mode</h3>



<ul>
<li>Meaning, compile with all warnings enabled.</li>



<li>This will allow the compiler to alert you to every issue it sees.</li>



<li>Treat your warnings as errors and address them before release.</li>
</ul>



<h3 class="wp-block-heading" id="rule-10-analyze-and-test">Rule #10 Analyze and test</h3>



<ul>
<li>Use multiple static code analyzers to evaluate your code
<ul>
<li>They don&#8217;t all work the same and sometimes use different rules.</li>
</ul>
</li>



<li>Test, test, and test again. Preferably with some form of automated testing, i.e. unit tests vs integration tests, etc.</li>
</ul>



<h2 class="wp-block-heading" id="resources-we-like">Resources We Like</h2>



<ul>
<li><a href="https://youtu.be/GWYhtksrmhE">https://youtu.be/GWYhtksrmhE</a></li>



<li><a href="https://en.wikipedia.org/wiki/The_Power_of_10:_Rules_for_Developing_Safety-Critical_Code">https://en.wikipedia.org/wiki/The_Power_of_10:_Rules_for_Developing_Safety-Critical_Code</a></li>
</ul>



<h2 class="wp-block-heading" id="tips-of-the-week">Tips of the Week</h2>



<ul>
<li>A couple years ago I mentioned an Instrumental album from a band called Night Verses that I was really excited about. It was great working music that kept things moving, and now they&#8217;ve gone and released a new album. The bass player from Tool (Justin Chancellor) guest stars on one of the tracks too.&nbsp;
<ul>
<li><a href="https://open.spotify.com/album/6JVvP0fi6y3Jz2mE0fUYPq">https://open.spotify.com/album/6JVvP0fi6y3Jz2mE0fUYPq</a></li>
</ul>
</li>



<li>View Pull Requests INSIDE IntelliJ
<ul>
<li><a href="https://www.jetbrains.com/help/idea/work-with-github-pull-requests.html">https://www.jetbrains.com/help/idea/work-with-github-pull-requests.html</a></li>
</ul>
</li>



<li>Or inside Visual Studio Code
<ul>
<li><a href="https://code.visualstudio.com/blogs/2018/09/10/introducing-github-pullrequests">https://code.visualstudio.com/blogs/2018/09/10/introducing-github-pullrequests</a></li>
</ul>
</li>



<li>Do AI locally using Llama 2 from Meta
<ul>
<li><a href="https://ai.meta.com/llama/">https://ai.meta.com/llama/</a></li>
</ul>
</li>



<li>Get started with ML and AI without having to find all the tools yourself using Anaconda
<ul>
<li><a href="https://www.anaconda.com/download">https://www.anaconda.com/download</a></li>



<li>They have installers for Linux, Mac and Windows</li>



<li>They also have a version that runs completely in the cloud so you could use a Chromebook if you wanted
<ul>
<li><a href="https://www.anaconda.com/code-in-the-cloud/">https://www.anaconda.com/code-in-the-cloud/</a></li>
</ul>
</li>



<li>You also get access to data science courses</li>
</ul>
</li>



<li>Maven build cache extension to improve local build times
<ul>
<li><a href="https://maven.apache.org/extensions/maven-build-cache-extension/">https://maven.apache.org/extensions/maven-build-cache-extension/</a></li>
</ul>
</li>
</ul>


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