c programming

13 Articles

ATtiny85 on circuit board with 2n2222, pushbutton, usb-c power connector, LED, and speaker.

Custom Compression Squeezes Classic Computer Choruses Into A Tiny Controller

August 19, 2021 by 14 Comments

Geeks of a certain vintage will have fond memories of games that were simplistic by today’s standards, but drew one in all the same. Their low fidelity graphics were often complimented by equally low fidelity music being forced through the afterthought of a speaker that inhabited most computers. Despite the technical constraints of the era, these games didn’t just offer gameplay. They told stories, and they were immersive in a way that some would think wouldn’t be relatable to a younger generation.

That didn’t stop [Thanassis Tsiodras] from sharing the classic “The Secret of Monkey Island” with his niece and nephew when they were young. Excited to see his family after a year of separation due to COVID-19, [Thanassis] wanted to give them a handmade gift: The music from “The Secret of Monkey Island” on a custom player. What an uncle!

[Thanassis] could have just recorded the music and played it back using any number of chips made for the purpose, but being a long time software engineer, he decided to take the scenic route to his destination. First, DOSBox was hacked to dump the speaker output into a file. Python, C, and 30 years of experience were leveraged to squeeze everything into the 8 KB storage of an ATtiny85. Doing so was no small feat, as it required that he create a custom implementation of Huffman compression to get the data small enough to fit on chip. And when it fit, but didn’t work, even more optimization was needed.

The end result was worth it however, with the music from “The Secret of Monkey Island” playing in its original form from a speaker driven by the ever so humble but useful 2n2222. [Thanassis]’ site is replete with details too intricate to post here, but too neat to miss. Watch the video below the break for a demonstration.

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Ask Hackaday: Is There A Legit Use For Operator Precedence?

February 19, 2019 by 111 Comments

Computing is really all about order. If you can take data, apply an operation to it, and get the same result every single time, then you have a stable and reliable computing system.

So it makes total sense that there is Operator Precedence. This is also called Order of Operations, and it dictates which computations will be performed first, and which will be performed last. To get the same results every time, you must perform addition, multiplication, power functions, bitwise math, and all other calculations in a codified order.

The question I’ve had on my mind lately is, does this matter to us or just the compiler?

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Crash Your Code – Lessons Learned From Debugging Things That Should Never Happen™

January 22, 2019 by 58 Comments

Let’s be honest, no one likes to see their program crash. It’s a clear sign that something is wrong with our code, and that’s a truth we don’t like to see. We try our best to avoid such a situation, and we’ve seen how compiler warnings and other static code analysis tools can help us to detect and prevent possible flaws in our code, which could otherwise lead to its demise. But what if I told you that crashing your program is actually a great way to improve its overall quality? Now, this obviously sounds a bit counterintuitive, after all we are talking about preventing our code from misbehaving, so why would we want to purposely break it?

Wandering around in an environment of ones and zeroes makes it easy to forget that reality is usually a lot less black and white. Yes, a program crash is bad — it hurts the ego, makes us look bad, and most of all, it is simply annoying. But is it really the worst that could happen? What if, say, some bad pointer handling doesn’t cause an instant segmentation fault, but instead happily introduces some garbage data to the system, widely opening the gates to virtually any outcome imaginable, from minor glitches to severe security vulnerabilities. Is this really a better option? And it doesn’t have to be pointers, or anything of C’s shortcomings in particular, we can end up with invalid data and unforeseen scenarios in virtually any language.

It doesn’t matter how often we hear that every piece of software is too complex to ever fully understand it, or how everything that can go wrong will go wrong. We are fully aware of all the wisdom and cliches, and completely ignore them or weasel our way out of it every time we put a /* this should never happen */ comment in our code.

So today, we are going to look into our options to deal with such unanticipated situations, how we can utilize a deliberate crash to improve our code in the future, and why the average error message is mostly useless.

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Warnings On Steroids – Static Code Analysis Tools

December 12, 2018 by 10 Comments

A little while back, we were talking about utilizing compiler warnings as first step to make our C code less error-prone and increase its general stability and quality. We know now that the C compiler itself can help us here, but we also saw that there’s a limit to it. While it warns us about the most obvious mistakes and suspicious code constructs, it will leave us hanging when things get a bit more complex.

But once again, that doesn’t mean compiler warnings are useless, we simply need to see them for what they are: a first step. So today we are going to take the next step, and have a look at some other common static code analysis tools that can give us more insight about our code.

You may think that voluntarily choosing C as primary language in this day and age might seem nostalgic or anachronistic, but preach and oxidate all you want: C won’t be going anywhere. So let’s make use of the tools we have available that help us write better code, and to defy the pitfalls C is infamous for. And the general concept of static code analysis is universal. After all, many times a bug or other issue isn’t necessarily caused by the language, but rather some general flaw in the code’s logic.

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Creating Black Holes: Division By Zero In Practice

November 21, 2018 by 31 Comments

Dividing by zero — the fundamental no-can-do of arithmetic. It is somewhat surrounded by mystery, and is a constant source for internet humor, whether it involves exploding microcontrollers, the collapse of the universe, or crashing your own world by having Siri tell you that you have no friends.

It’s also one of the few things gcc will warn you about by default, which caused a rather vivid discussion with interesting insights when I recently wrote about compiler warnings. And if you’re running a modern operating system, it might even send you a signal that something’s gone wrong and let you handle it in your code. Dividing by zero is more than theoretical, and serves as a great introduction to signals, so let’s have a closer look at it.

Chances are, the first time you heard about division itself back in elementary school, it was taught that dividing by zero is strictly forbidden — and obviously you didn’t want your teacher call the cops on you, so you obeyed and refrained from it. But as with many other things in life, the older you get, the less restrictive they become, and dividing by zero eventually turned from forbidden into simply being impossible and yielding an undefined result.

And indeed, if a = b/0, it would mean in reverse that a×0 = b. If b itself was zero, the equation would be true for every single number there is, making it impossible to define a concrete value for a. And if b was any other value, no single value multiplied by zero could result in anything non-zero. Once we move into the realms of calculus, we will learn that infinity appears to be the answer, but that’s in the end just replacing one abstract, mind-boggling concept with another one. And it won’t answer one question: how does all this play out in a processor? Continue reading “Creating Black Holes: Division By Zero In Practice” →

Warnings Are Your Friend – A Code Quality Primer

November 6, 2018 by 63 Comments

If there’s one thing C is known and (in)famous for, it’s the ease of shooting yourself in the foot with it. And there’s indeed no denying that the freedom C offers comes with the price of making it our own responsibility to tame and keep the language under control. On the bright side, since the language’s flaws are so well known, we have a wide selection of tools available that help us to eliminate the most common problems and blunders that could come back to bite us further down the road. The catch is, we have to really want it ourselves, and actively listen to what the tools have to say.

We often look at this from a security point of view and focus on exploitable vulnerabilities, which you may not see as valid threat or something you need to worry about in your project. And you are probably right with that, not every flaw in your code will lead to attackers taking over your network or burning down your house, the far more likely consequences are a lot more mundane and boring. But that doesn’t mean you shouldn’t care about them.

Buggy, unreliable software is the number one cause for violence against computers, and whether you like it or not, people will judge you by your code quality. Just because Linus Torvalds wants to get off Santa’s naughty list, doesn’t mean the technical field will suddenly become less critical or loses its hostility, and in a time where it’s never been easier to share your work with the world, reliable, high quality code will prevail and make you stand out from the masses.

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It’s All In The Libs – Building A Plugin System Using Dynamic Loading

July 12, 2018 by 17 Comments

Shared libraries are our best friends to extend the functionality of C programs without reinventing the wheel. They offer a collection of exported functions, variables, and other symbols that we can use inside our own program as if the content of the shared library was a direct part of our code. The usual way to use such libraries is to simply link against them at compile time, and let the linker resolve all external symbols and make sure everything is in place when creating our executable file. Whenever we then run our executable, the loader, a part of the operating system, will try to resolve again all the symbols, and load every required library into memory, along with our executable itself.

But what if we didn’t want to add libraries at compile time, but instead load them ourselves as needed during runtime? Instead of a predefined dependency on a library, we could make its presence optional and adjust our program’s functionality accordingly. Well, we can do just that with the concept of dynamic loading. In this article, we will look into dynamic loading, how to use it, and what to do with it — including building our own plugin system. But first, we will have a closer look at shared libraries and create one ourselves.

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