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
How fast is rolling Karp-Rabin hashing?
A hash function maps values (e.g., strings) into a fixed number of strings, typically smaller than the original. It is useful to compare quickly two long strings...
From Daniel Lemire's Blog
C23: a slightly better C
One of the established and most popular programming languages is the C programming language. It is relatively easy to learn, and highly practical. Maybe surprisingly...
From Daniel Lemire's Blog
How much memory bandwidth do large Amazon instances offer?
In my previous post, I described how you can write a C++ program to estimate your read memory bandwidth. It is not very difficult: you allocate a large memory region...
From Daniel Lemire's Blog
Estimating your memory bandwidth
One of the limitations of a compute is the memory bandwidth. For the scope of this article, I define “memory bandwidth” as the maximal number of bytes you can bring...
From Daniel Lemire's Blog
Implementing the missing sign instruction in AVX-512
Intel and AMD have expanded the x64 instruction sets over time. In particular, the SIMD (Single instruction, multiple data) instructions have become progressively...
From Daniel Lemire's Blog
Science and Technology links (December 30th 2023)
Parenting does not appear to be able to determine the personality traits of a child. When the last ice age ended, 12,000 years ago, the Sahara was green and full...
From Daniel Lemire's Blog
Measuring the size of the cache line empirically
Our computers do not read or write memory in units of bits or even bytes. Rather memory is accessed in small blocks of memory called “cache line”. For a given system...
From Daniel Lemire's Blog
Fast Buffer-to-String conversion in JavaScript with a Lookup Table
When programming in a JavaScript environment such as Node.js, you might recover raw data from the network and need to convert the bytes into strings. In a system...
From Daniel Lemire's Blog
How fast can you validate UTF-8 strings in JavaScript?
When you recover textual content from the disk or from the network, you may expect it to be a Unicode string in UTF-8. It is the most common format. Unfortunately...
From Daniel Lemire's Blog
Parsing 8-bit integers quickly
Suppose that you want to parse quickly 8-bit integers (0, 1, 2, …, 254, 255) from an ASCII/UTF-8 string. The problem comes up in the simdzone project lead by Jeroen...
From Daniel Lemire's Blog
A simple WebSocket benchmark in Python
Modern web applications often use the http/https protocols. However, when the server and client needs to talk to each other in a symmetrical fashion, the WebSocket...
From Daniel Lemire's Blog
A simple WebSocket benchmark in JavaScript: Node.js versus Bun
Conventional web applications use the http protocol (or the https variant). The http protocol is essentially asymmetrical: a client application such as a browser...
From Daniel Lemire's Blog
Science and Technology links (November 12 2023)
Vitamin K2 supplements might reduce the risk of myocardial infarction (heart attacks) and of all-cause death (Hasific et al. 2022). You find vitamin K2 in someContinue...
From Daniel Lemire's Blog
Generating arrays at compile-time in C++ with lambdas
Suppose that you want to check whether a character in C++ belongs to a fixed set, such as ‘\0’, ‘\x09’, ‘\x0a’,’\x0d’, ‘ ‘, ‘#’, ‘/’, ‘:’, ‘<‘, ‘>’, ‘?’, ‘@’, ‘...
From Daniel Lemire's Blog
Appending to an std::string character-by-character: how does the capacity grow?
In C++, suppose that you append to a string one character at a time: while(my_string.size() <= 10'000'000) { my_string += "a"; } In theory, it might be possible...
From Daniel Lemire's Blog
For processing strings, streams in C++ can be slow
The C++ library has long been organized around stream classes, at least when it comes to reading and parsing strings. But streams can be surprisingly slow. ForContinue...
From Daniel Lemire's Blog
How many billions of transistors in your iPhone processor?
In about 10 years, Apple has multiplied by 19 the number of transistors in its mobile processors. It corresponds roughly to a steady rate of improvement of 34%Continue...
From Daniel Lemire's Blog
Randomness in programming (with Go code)
Computer software is typically deterministic on paper: if you run twice the same program with the same inputs, you should get the same outputs. In practice, the...
From Daniel Lemire's Blog
Parsing integers quickly with AVX-512
If I give a programmer a string such as "9223372036854775808" and I ask them to convert it to an integer, they might do the following in C++: std::string s = .....
From Daniel Lemire's Blog