A binary search is not a very interesting topic as it is a well known and fairly simple algorithm. However, I have encountered an interesting variant of it lately – one that I would like to share.
The Linux Kernel defines one Jiffy as the period of time between two consecutive system timer interrupts, and keeps a “jiffies” counter. Having jiffies, the next handy parameter would be the amount of delay-loop iterations that the CPU is able to fit in a single jiffy. With this number at hand (and known timer frequency) the kernel is able to support fine-grained execution delays, for instance. How would you implement computation of said “loops_per_jiffy” parameter?
Continue reading Bitwise binary search
Every programming language has its benefits and its drawbacks. Python, for example, provides a dynamic and clean environment for the developer, which boosts productivity by hiding much of the “dirty work”: memory management, type inference (duck typing, in this case), and more. Such benefits usually come at the cost of efficiency, which is something that other programming languages (such as C++) excel in.
The next logical step would then be a way to combine the benefits of such different programming languages in a single system. For instance, we could use C++ solely for the cpu-intensive parts, while the rest of the software could very well be written entirely in Python. The missing piece would then be a way to integrate the two. The common way of doing so is through SWIG, which is a tool that is able to wrap C++ to many different programming languages, Python included. Using SWIG right out of the box, we will be able to invoke C++ code directly from a Python interpreter. But what if we wanted to extend C++ classes in Python, making native C++ seamlessly call Python code?
Continue reading Python directing C++
A few months ago I have been to the states. Naturally, one big outcome of that trip was a handful of photographs documenting it – 1.6GB of these, to be precise. The bad part is that I have forgotten to reset the camera settings beforehand, which made all the pictures date a few years back.
The images I made with my Cannon camera (sx110) use JPEG for compression, and Exif for the metadata – including the date and time the picture was taken, which is what we’re interested in. Being as perfectionist as I am, and having some familiarity with Python, I set out to modify the metadata on the pictures to contain the right dates for the trip.
Continue reading Fixing incorrect photo data
Writing fairly straightforward C++ code, we usually make heavy use of the RAII concept. Therefore, we greatly rely on the simple (and basic) assumption that all appropriate destructors will be called. What happens if that is not the case?
Continue reading Unexpected skip of a destructor
A priority queue in the STL is nothing more than a regular (maximum-) heap. It is essentially an adapter built on top of another container, usually a vector. Therefore, the offered priority queue can easily contain an arbitrary number of elements (so long as memory permits).
But what if we wanted to keep only the biggest N elements, and just have the queue dynamically throw away all other elements? I am sure you can imagine why such a behavior would be much desired: for instance, keeping the best N suggestions for a specific search term springs to mind. Unfortunately, the STL does not support such an adapter.
Continue reading Bounded size priority queue