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arXiv · 2604.26019

Converting an Integer to a Decimal String in Under Two Nanoseconds

Jaël Champagne Gareau·Daniel Lemire
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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.

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Jaël Champagne Gareau, Daniel Lemire. 2026-04-28. Converting an Integer to a Decimal String in Under Two Nanoseconds. https://doi.org/10.1002/spe.70079

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