Tips and Tricks For The C Pre-Processor

The C pre-processor can help you write more concise, easy to follow code. It can also let you create a tangled ball of macros and #defines. [s1axter] wrote up a guide on how to use the pre-processor and keep your sanity.

We’ve seen some neat hacks with the C pre-processor, such as a full adder implementation, but this focuses on more practical usages. First, [s1axter] explains what the pre-processor does with your code by writing simple macros. Next up is arguments, and usage of ‘##’ directive for metaprogramming. Finally, we get a good explanation of why you need to worry about scope when using macros, and how to safe code by using ‘do {} while()’ statements.

If you’re into embedded programming, this guide will help you understand some of the more complex pre-processor techniques out there. It’s helpful for making your code clearer, and abstracting away hardware dependencies in a few lines of code.

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Trimming The Fat From AVR GCC

[Ralph] has been working on an extraordinarily tiny bootloader for the ATtiny85, and although coding in assembly does have some merits in this regard, writing in C and using AVR Libc is so much more convenient. Through his trials of slimming down pieces of code to the bare minimum, he’s found a few ways to easily trim a few bytes off code compiled with AVR-GCC.

To test his ideas out, [Ralph] first coded up a short program that reads the ATtiny85′s internal temperature sensor. Dissassembling the code, he found the a jump to a function called __ctors_end: before the jump to main. According to the ATtiny85 datasheet, this call sets the IO registers to their initial values. These initial values are 0, so that’s 16 bytes that can be saved. This function also sets the stack pointer to its initial value, so another 16 bytes can be optimized out.

If you’re not using interrupts on an ATtiny, you can get rid of 30 bytes of code by getting rid of the interrupt vector table. In the end, [Ralph] was able to take a 274 byte program and trim it down to 190 bytes. Compared to the 8k of Flash on the ‘tiny85, it’s a small amount saved, but if you’re banging your head against the limitations of this micro’s storage, this might be a good place to start.

Now if you want to hear some stories about optimizing code you’ve got to check out the Once Upon Atari documentary. They spent months hand optimizing code to make it fit on the cartridges.

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3-Sweep: Turning 2D Images into 3D Models

As 3D printing continues to grow, people are developing more and more ways to get 3D models. From the hardware based scanners like the Microsoft Kinect to software based like 123D Catch there are a lot of ways to create a 3D model from a series of images. But what if you could make a 3D model out of a single image? Sound crazy? Maybe not. A team of researchers have created 3-Sweep, an interactive technique for turning objects in 2D images into 3D models that can be manipulated.

To be clear, the recognition of 3D components within a single image is a bit out of reach for computer algorithms alone. But by combining the cognitive abilities of a person with the computational accuracy of a computer they have been able to create a very simple tool for extracting 3D models. This is done by outlining the shape similar to how one might model in a CAD package — once the outline is complete, the algorithm takes over and creates a model.

The software was debuted at Siggraph Asia 2013 and has caused quite a stir on the internet. Watch the fascinating video that demonstrates the software process after the break!

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