Converting an Integer to a Decimal String in Under Two Nanoseconds

TL;DR

This paper presents a SIMD-based algorithm for converting integers to decimal strings that is faster than existing methods, eliminating lookup tables and adapting to input characteristics.

Contribution

A novel SIMD algorithm for integer to decimal string conversion that outperforms existing methods and adapts dynamically to input data.

Findings

Runs 1.4-2x faster than closest competitors

Outperforms std::to_chars by 2-4x across workloads

Eliminates lookup tables and uses parallel processing

Abstract

Converting binary integers to variable-length decimal strings is a fundamental operation in computing. Conventional fast approaches rely on recursive division and small lookup tables. We propose a SIMD-based algorithm that leverages integer multiply-add instructions available on recent AMD and Intel processors. Our method eliminates lookup tables entirely and computes multiple quotients and remainders in parallel. Additionally, we introduce a dual-variant design with dynamic selection that adapts to input characteristics: a branch-heavy variant optimized for homogeneous digit-length distributions and a branch-light variant for heterogeneous datasets. Our single-core algorithm consistently outperforms all competing methods across the full range of integer sizes, running 1.4-2x faster than the closest competitor and 2-4x faster than the C++ standard library function std::to_chars across tested workloads.