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
Quickly checking that a string belongs to a small set
Suppose that I give you a set of reference strings (“ftp”, “file”, “http”, “https”, “ws”, “wss”). Given a new string, you want to quickly tell whether it is part...
From Daniel Lemire's Blog
Science and Technology links (December 25 2022)
One of Elon Musk’s ventures, OpenAI, made public a new tool called ChatGPT. It is widely regarding as a practical breakthrough in artificial intelligence. Given...
From Daniel Lemire's Blog
Fast base16 encoding
Given binary data, we often need to encode it as ASCII text. Email and much of the web effectively works in this manner. A popular format for this purpose is base64...
From Daniel Lemire's Blog
The size of things in bytes
storing 1 GiB/month on the cloud 0.02$US web site of my twitter profile (@lemire), HTML alone 296 KiB web site of my twitter profile (@lemire), all data 3.9 MiB...
From Daniel Lemire's Blog
Checking for the absence of a string, naive AVX-512 edition
Suppose you would like to check that a string is not present in a large document. In C, you might do the following using the standard function strstr: bool is_present...
From Daniel Lemire's Blog
What is the memory usage of a small array in C++?
In an earlier blog post, I reported that the memory usage of a small byte array in Java (e.g., an array containing 4 bytes) was about 24 bytes. In other words:Continue...
From Daniel Lemire's Blog
Science and Technology links (December 11 2022)
As we focus on some types of unfortunate discrimination (race, gender), we may become blind to other types of discrimination. For example, tend to discrimate against...
From Daniel Lemire's Blog
Fast midpoint between two integers without overflow
Let us say that I ask you to find the number I am thinking about between -1000 and 1000, by repeatedly guessing a number. With each guess, I tell you whether your...
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