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
Memory-level parallelism : Intel Ice Lake versus Amazon Graviton 3
One of the most expensive operation in a processor and memory system is a random memory access. If you try to read a value in memory, it can take tens of nanosecond...
From Daniel Lemire's Blog
Data structure size and cache-line accesses
On many systems, memory is accessed in fixed blocks called “cache lines”. On Intel systems, the cache line spans 64 bytes. That is, if you access memory at byte...
From Daniel Lemire's Blog
Parsing JSON faster with Intel AVX-512
Many recent Intel processors benefit from a new family of instructions called AVX-512. These instructions operate over wide registers (up to 512 bits) and follow...
From Daniel Lemire's Blog
Avoid exception throwing in performance-sensitive code
There are various ways in software to handle error conditions. In C or Go, one returns error code. Other programming languages like C++ or Java prefer to throwContinue...
From Daniel Lemire's Blog
Faster bitset decoding using Intel AVX-512
I refer to “bitset decoding” as the action of finding the positions of the 1s in a stream of bits. For example, given the integer value 0b11011 (or 27 in decimal)...
From Daniel Lemire's Blog
Fast bitset decoding using Intel AVX-512
In software, we often use ‘bitsets’: you work with arrays of bits to represent sets of small integers. It is a concise and fast data structure. Sometimes you want...
From Daniel Lemire's Blog
Removing characters from strings faster with AVX-512
In software, it is a common problem to want to remove specific characters from a string. To make the problem precise, let us consider the removal of all ASCII control...
From Daniel Lemire's Blog
An overview of version control in programming
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...
From Daniel Lemire's Blog
Floats have 15-digit accuracy in their normal range
In programming languages like JavaScript or Python, numbers are typically represented using 64-bit IEEE number types (binary64). For these numbers, we have 15 digits...
From Daniel Lemire's Blog
String representations are not unique: learn to normalize!
Most strings in software today are represented using the unicode standard. The unicode standard can represent most human readable strings. Unicode works by representing...
From Daniel Lemire's Blog
Converting integers to decimal strings faster with AVX-512
In most systems, integers are stored using a fixed binary representation. It is common to store integers using 32-bit or 64-bit words. You sometimes need to convert...
From Daniel Lemire's Blog
Writing out large arrays in Go: binary.Write is inefficient for large arrays
Programmers often need to write data structures to disk or to networks. The data structure then needs to be interpreted as a sequence of bytes. Regarding integer...
From Daniel Lemire's Blog
Enforcement by software
At my university, one of our internal software systems allows a professor to submit a revision to a course. The professor might change the content or the objectives...
From Daniel Lemire's Blog
The Canadian Common CV and the captured academy
Most Canadian academics have to write their resumes using a government online tool called the Common CV. When it was first introduced, it was described as a time...
From Daniel Lemire's Blog
How many digits in a product?
We often represent integers with digits. E.g., the integer 1234 has 4 digits. By extension, we use ‘binary’ digits, called bits, within computers. Thus the integer...
From Daniel Lemire's Blog
The end of the monopolistic web era?
Except maybe in totalitarian states, you cannot ever have a single publisher. Most large cities had multiple independent newspapers. In recent years, we saw a surge...
From Daniel Lemire's Blog
SWAR explained: parsing eight digits
It is common to want to parse long strings of digits into integer values. Because it is a common task, we want to optimize it as much as possible. In the blog post...
From Daniel Lemire's Blog
What is the ‘range’ of a number type?
In programming, we often represent numbers using types that have specific ranges. For example, 64-bit signed integer types can represent all integers between -9223372036854775808...
From Daniel Lemire's Blog
How programmers make sure that their software is correct
Our most important goal in writing software is that it be correct. The software must do what the programmer wants it to do. It must meet the needs of the user.Continue...
From Daniel Lemire's Blog