Schubfach

A C++ implementation of the Schubfach algorithm - fast and accurate conversion of IEEE-754 double values to decimal strings.

For a faster method see https://github.com/vitaut/zmij.

Usage:

#include "schubfach.h"
#include <stdio.h>

int main() {
  char buf[schubfach::buffer_size];
  schubfach::dtoa(6.62607015e-34, buf);
  puts(buf);
}

Average formatting time from dtoa-benchmark, smaller is better:

Function	Time (ns)	Speedup
ostringstream	880.245	1.00x
sprintf	742.654	1.19x
doubleconv	83.629	10.53x
ryu	37.184	23.67x
schubfach	24.865	35.40x
fmt	22.331	39.42x
dragonbox	20.782	42.36x

The binary size is ~12kiB on an ARM-based macOS:

% c++ -c -Os -DNDEBUG -std=c++20 schubfach.cc
% du -Ah schubfach.o
 12K	schubfach.o

Build time is ~77ms by default and ~95ms with optimizations enabled as measured by

% time c++ -c -std=c++20 schubfach.cc [-O2]

taking the best of 3 runs.