Floating-point numbers are ancient, mysterious, and terrifying. Over the past 30 years, the C and C++ Standards have provided many functions for floating-point/string conversions, such as C's strtof(), strtod(), and printf() %a %e %f %g, and C++'s iostreams, stof(), stod(), and to_string(). Despite this history, floating-point is far from a solved problem - these functions have ranged from annoyingly to egregiously slow, and application developers and library maintainers alike have found it exceedingly difficult to understand floating-point behavior.

This session will present new and wondrous developments in the area of floating-point conversions. If your serialization code is bottlenecked by floating-point printing, this will accelerate your code by roughly 3x to 30x (yes, times, not percent). You can also improve the human-readability of your output. Along the way, this session will cover the basics of floating-point representations, dispelling common myths like fuzziness and non-determinism.

Specifically, C++17 added 3 pages of Standardese describing the charconv header and its functions from_chars() and to_chars(). This feature has required an unexpectedly large amount of implementation work, taking over a dev-year for MSVC and becoming the last C++17 library feature to ship. Coincidentally, Ulf Adams at Google developed a novel algorithm named Ryu, which is responsible for the amazing speed of to_chars(). This session will focus on how to use charconv and how to understand its many supported formats, with a brief overview of Ryu's techniques.