The Fastest dtoa Algorithm Has No Paper and No Name — It Lives in a Single File Inside yyjson

vitaut.net (corroborated by Lobsters; r/programming 152up/25c)·medium signalXBlueskyLinkedInCopy link

Victor Zverovich (vitaut, author of fmt) published a post on 2026-08-10 about 'yy', a Schubfach-family binary-to-decimal algorithm that lives in yy_double.c inside ibireme's yyjson and has essentially no public profile outside the JSON performance crowd. Its trick is needing only one multiplication by a precomputed power of ten where classic Schubfach needs two or three, while still finding the shortest round-tripping decimal. The Żmij library reportedly switched its core from Schubfach (34.58 ns) to yy (16.61 ns) and, with further optimization, reached 3.93 ns — a reminder that the fastest implementation of a well-studied primitive can sit unnamed in a vendored C file.