README.md

Ryu

This project contains a C and a Java implementation of Ryu, an algorithm to quickly convert floating point numbers to decimal strings. We have tested the code on Ubuntu 17.10, MacOS High Sierra, and Windows 10.

The Java implementations are RyuFloat and RyuDouble under src/main/java/. The C implementation is in the ryu/ directory. Both cover 32 and 64-bit floating point numbers.

All code outside of third_party/ is Copyright Ulf Adams, and may be used in accordance with the Apache 2.0 license. Alternatively, the files in the ryu/ directory may be used in accordance with the Boost 1.0 license.

Building, Testing, Running

We use the Bazel build system (https://bazel.build). We recommend using the latest release, but it should also work with earlier versions. You also need to install Jdk 8 and a C/C++ compiler (gcc or clang on Ubuntu, XCode on MacOS, or MSVC on Windows).

Building with a Custom Compiler

You can select a custom C++ compiler by setting the CC environment variable (e.g., on Ubuntu, run export CC=clang-3.9).

For example, use these steps to build with clang-4.0:

$ export CC=clang-4.0
$ bazel build //ryu

Note that older Bazel versions (< 0.14) did not work with all compilers (https://github.com/bazelbuild/bazel/issues/3977).

Tests

You can run both C and Java tests with

$ bazel test //ryu/... //src/...

Computing Required Lookup Table Sizes

You can compute the required lookup table sizes with:

$ bazel run //src/main/java/info/adams/ryu/analysis:ComputeTableSizes --

Add -v to get slightly more verbose output.

Computing Required Bit Sizes

You can compute the required bit sizes with:

$ bazel run //src/main/java/info/adams/ryu/analysis:ComputeRequiredBitSizes --

Add the -128 and -256 flags to also cover 128- and 256-bit numbers. This could take a while - 128-bit takes ~20 seconds on my machine while 256-bit takes a few hours. Add -v to get very verbose output.

Java: Comparing All Possible 32-bit Values Exhaustively

You can check the slow vs. the fast implementation for all 32-bit floating point numbers using:

$ bazel run //src/main/java/info/adams/ryu/analysis:ExhaustiveFloatComparison

This takes ~60 hours to run to completion on an Intel(R) Core(TM) i7-4770K with 3.50GHz.

Java: Comparing All Possible 64-bit Values Exhaustively

You can check the slow vs. the fast implementation for all 64-bit floating point numbers using:

$ bazel run //src/main/java/info/adams/ryu/analysis:ExtensiveDoubleComparison

However, this takes approximately forever, so you will need to interrupt the program.

Benchmarks

We provide both C and Java benchmark programs.

Enable optimization by adding "-c opt" on the command line:

$ bazel run -c opt //ryu/benchmark --
    Average & Stddev Ryu  Average & Stddev Grisu3
32:   22.515    1.578       90.981   41.455
64:   27.545    1.677       98.981   80.797

$ bazel run //src/main/java/info/adams/ryu/benchmark --
    Average & Stddev Ryu  Average & Stddev Jdk  Average & Stddev Jaffer
32:   56.680    9.127       254.903  170.099
64:   89.751   13.442      1085.596  302.371     1089.535  309.245

Additional parameters can be passed to the benchmark after the -- parameter:

  -32           only run the 32-bit benchmark
  -64           only run the 64-bit benchmark
  -samples=n    run n pseudo-randomly selected numbers
  -iterations=n run each number n times
  -v            generate verbose output in CSV format

If you have gnuplot installed, you can generate plots from the benchmark data with:

$ bazel build --jobs=1 //scripts:{c,java}-{float,double}.pdf

The resulting files are bazel-genfiles/scripts/{c,java}-{float,double}.pdf.

Building without Bazel on Linux / MacOS

You can build and run the C benchmark without using Bazel with the following shell command:

$ gcc -o benchmark -I. -O2 -l stdc++ ryu/*.c ryu/benchmark/benchmark.cc \
    third_party/double-conversion/double-conversion/*.cc \
    third_party/mersenne/*.c
$ ./benchmark

You can build and run the Java benchmark with the following shell command:

$ mkdir out
$ javac -d out \
    -sourcepath src/main/java/:third_party/mersenne_java/java/:third_party/jaffer/java/ \
    src/main/java/info/adams/ryu/benchmark/BenchmarkMain.java
$ java -cp out info.adams.ryu.benchmark.BenchmarkMain

Comparison with Other Implementations

Grisu3

Ryu's output should exactly match Grisu3's output. Our benchmark verifies that the generated numbers are identical.

$ bazel run -c opt //ryu/benchmark -- -64
    Average & Stddev Ryu  Average & Stddev Grisu3
64:   29.806    3.182      103.060   98.717

Jaffer's Implementation

The code given by Jaffer in the original paper does not come with a license declaration. Instead, we're using code found on GitHub, which contains a license declaration by Jaffer. Compared to the original code, this implementation no longer outputs incorrect values for negative numbers.

Differences between Ryu and Jaffer / Jdk implementations

We provide a binary to find differences between Ryu and the Jaffer / Jdk implementations:

$ bazel run //src/main/java/info/adams/ryu/analysis:FindDifferences --

Add the -mode=csv option to get all the discovered differences as a CSV. Use -mode=latex instead to get a latex snippet of the first 20. Use -mode=summary to only print the number of discovered differences (this is the default mode).