Communications of the ACM
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How the “Frontier” Became the Slogan of Uncontrolled AI
Artificial intelligence (AI) has been billed as the next frontier of humanity: the newly available expanse whose exploration …
From Daniel Lemire's Blog
Optimizing compilers reload vector constants needlessly
Modern processors have powerful vector instructions which allow you to load several values at once, and operate (in one instruction) on all these values. Similarly...
From Daniel Lemire's Blog
How big are your SVE registers ? (AWS Graviton)
Amazon has some neat ARM-based systems based on Amazon’s own chips (Graviton). You can access them through Amazon’s web services (AWS). These processors have advanced...
From Daniel Lemire's Blog
Generic number compression (zstd)
I have done a lot of work that involves compressing and uncompressing data. Most often, I work on data that has specific characteristics, e.g., sorted integers....
From Daniel Lemire's Blog
Science and Technology links (November 26 2022)
Molière’s famous play, Tartuffe, the main characters is outwardly pious but fundamentally deceitful. Are people who insist on broadcasting their high virtue better...
From Daniel Lemire's Blog
Making all your integers positive with zigzag encoding
You sometimes feel the need to make all of your integers positive, without losing any information. That is, you want to map all of your integers from ‘signed’ integers...
From Daniel Lemire's Blog
What is the size of a byte[] array in Java?
Java allows you to create an array just big enough to contain 4 bytes, like so: byte[] array = new byte[4]; How much memory does this array take? If you have answered...
From Daniel Lemire's Blog
Rounding modes: std::from_chars versus strtod/strtof
A recent C++ standard (C++17) introduced new functions to parse floating-point numbers std::from_chars, from strings (e.g., ASCII text) to binary numbers. How should...
From Daniel Lemire's Blog
A fast function to check your floating-point rounding mode
For speed, we use finite-precision number types in software. When doing floating-point computations in software, the results are usually not exact. For example,...
From Daniel Lemire's Blog
Measuring the memory usage of your C++ program
In C++, we might implement dynamic lists using the vector template. The int-valued constructor of the vector template allocates at least enough memory to storeContinue...
From Daniel Lemire's Blog
Modern vector programming with masked loads and stores
When you start a program, it creates a ‘process’ which own its memory. Memory is allocated to a software process in blocks called ‘pages’. These pages might span...
From Daniel Lemire's Blog
Book Review : Template Metaprogramming with C++
I have spent the last few years programming often in C++. The C++ langage is probably one of the hardest to master. I still learn something new every week. Furthermore...
From Daniel Lemire's Blog
Science and Technology links (October 16 2022)
Doctors in Israel are toying with polygenic screening: it is a way to make it more likely that your baby will grow up to be healthy. In 2021, 337 million prescriptions...
From Daniel Lemire's Blog
The number of comparisons needed to sort a shuffled array: qsort versus std::sort
Given an array of N numbers of type double, the standard way to sort it in C is to invoke the qsort function qsort(array, N, sizeof(double), compare); where compare...
From Daniel Lemire's Blog
A review of elementary data types : numbers and strings
Computer programming starts with the organization of the data into data structures. In almost all cases, we work with strings or numbers. It is critical to understand...
From Daniel Lemire's Blog
Optimizing compilers deduplicate strings and arrays
When programming, it can be wasteful to store the same constant data again and again. You use more memory, you access more data. Thankfully, your optimizing compiler...
From Daniel Lemire's Blog
Science and Technology links (September 16 2022)
Attractive female students get better grades. They lose this benefit when courses move online. A research paper is much more likely to be highly ranked if the author...
From Daniel Lemire's Blog
Escaping strings faster with AVX-512
When programming, we often have to ‘escape’ strings. A standard way to do it is to insert the backslash character (\) before some characters such as the doubleContinue...
From Daniel Lemire's Blog
Science and Technology links (September 12 2022)
A standard dataset in artificial-intelligence research has ten percent of its images mislabeled. Yet state-of-the-art algorithms achieve better-than-90% classification...
From Daniel Lemire's Blog
Catching sanitizer errors programmatically
The C and C++ languages offer little protection against programmer errors. Errors do not always show up where you expect. You can silently corrupt the content of...
From Daniel Lemire's Blog