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In software, it is common to represent time as a time-stamp string. It is usually specified by a time format string. Some standards use the format %Y%m%d%H%M%S meaning that we print the year, the month, the day, the hours, the minutes and the seconds. The current time as I write this blog post would be 20230701205436 as a time stamp in this format. It is convenient because it is short, easy to rea

Daniel Lemire's blog Daniel Lemire is a software performance expert. He ranks among the top 2% of scientists globally (Stanford/Elsevier 2024) and is one of GitHub's top 1000 most followed developers. Menu and widgets

In practice, computer code is constantly being transformed. At the beginning of a project, the computer code often takes the form of sketches that are gradually refined. Later, the code can be optimized or corrected, sometimes for many years. Soon enough, programmers realized that they needed to not only to store files, but also to keep track of the different versions of a given file. It is no acc

In the C programming language, we allocate memory dynamically (on the heap) using the malloc function. You pass malloc a size parameter corresponding to the number of bytes you need. The function returns either a pointer to the allocated memory or the NULL pointer if the memory could not be allocated. Or so you may think. Let us write a program that allocates 1 terabytes of memory and then tries t

Daniel Lemire's blog Daniel Lemire is a software performance expert. He ranks among the top 2% of scientists globally (Stanford/Elsevier 2024) and is one of GitHub's top 1000 most followed developers. Menu and widgets

Daniel Lemire's blog Daniel Lemire is a software performance expert. He ranks among the top 2% of scientists globally (Stanford/Elsevier 2024) and is one of GitHub's top 1000 most followed developers. Menu and widgets

Daniel Lemire's blog Daniel Lemire is a software performance expert. He ranks among the top 2% of scientists globally (Stanford/Elsevier 2024) and is one of GitHub's top 1000 most followed developers. Menu and widgets

Computers store data as streams of bits. Binary files like image, audio or video files are allowed to contain just about any sequence of bits. However, we also often use text formats; for example, web pages and emails are required to be text. So how do we send images by email? How do we embed images within web pages? One possibility is to point to a distinct binary file. Another common approach is

Daniel Lemire's blog Daniel Lemire is a software performance expert. He ranks among the top 2% of scientists globally (Stanford/Elsevier 2024) and is one of GitHub's top 1000 most followed developers. Menu and widgets

Daniel Lemire's blog Daniel Lemire is a software performance expert. He ranks among the top 2% of scientists globally (Stanford/Elsevier 2024) and is one of GitHub's top 1000 most followed developers. Menu and widgets

Daniel Lemire's blog Daniel Lemire is a software performance expert. He ranks among the top 2% of scientists globally (Stanford/Elsevier 2024) and is one of GitHub's top 1000 most followed developers. Menu and widgets

Some of the latest Intel processors support the AVX-512 family of vector instructions. These instructions operate on blocks of 512 bits (or 64 bytes). The benefit of such wide instructions is that even without increasing the processor clock speed, systems can still process a lot more data. Most code today operators over 64-bit words (8 bytes). In theory, keeping everything else constant, you could

So it is four times faster! No bad. As usual, my code is freely available. What can this be good for? Well… if you have been forcing your arrays and hash tables to have power-of-two capacities to avoid expensive divisions, you may be able to use the fast range map to support arbitrary capacities without too much of a performance penalty. You can also generate random numbers in a range faster, whic

Last year, we published a fast C++ library to quickly compress and decompress arrays of integers. To get good compression, we use differential coding: the arrays of integers are sorted and instead of storing the integers themselves, we store the difference between successive integers. The differences are typically small integers that can be compressed efficiently. Out of habit, I ported our code t

Daniel Lemire's blog Daniel Lemire is a software performance expert. He ranks among the top 2% of scientists globally (Stanford/Elsevier 2024) and is one of GitHub's top 1000 most followed developers. Menu and widgets

Daniel Lemire's blog Daniel Lemire is a software performance expert. He ranks among the top 2% of scientists globally (Stanford/Elsevier 2024) and is one of GitHub's top 1000 most followed developers. Menu and widgets

Daniel Lemire's blog Daniel Lemire is a software performance expert. He ranks among the top 2% of scientists globally (Stanford/Elsevier 2024) and is one of GitHub's top 1000 most followed developers. Menu and widgets