This commit provides an alternative implementation for a float → decimal conversion. It integrates a C implementation of Fabian Loitsch's Grisu-algorithm [[pdf]](http://florian.loitsch.com/publications/dtoa-pldi2010.pdf), extracted from https://github.com/night-shift/fpconv. The relevant files are added in this PR, they are, as is all of https://github.com/night-shift/fpconv, available under a MIT License. As a result, I see a speedup of 900% on Apple Silicon M1 for a float set of benchmarks. floats don't have a single correct string representation: a float like `1000.0` can be represented as "1000", "1e3", "1000.0" (and more). The Grisu algorithm converts floating point numbers to an optimal decimal string representation without loss of precision. As a result, a float that is exactly an integer (like `Float(10)`) will be converted by that algorithm into `"10"`. While technically correct – the JSON format treats floats and integers identically –, this differs from the current behaviour of the `"json"` gem. To address this, the integration checks for that case, and explicitely adds a ".0" suffix in those cases. This is sufficient to meet all existing tests; there is, however, a chance that the current implementation and this implementation occasionally encode floats differently. ``` == Encoding floats (4179311 bytes) ruby 3.4.1 (2024-12-25 revision https://github.com/ruby/json/commit/48d4efcb85) +YJIT +PRISM [arm64-darwin24] Warming up -------------------------------------- json (local) 4.000 i/100ms Calculating ------------------------------------- json (local) 46.046 (± 2.2%) i/s (21.72 ms/i) - 232.000 in 5.039611s Normalize to 2090234 byte == Encoding floats (4179242 bytes) ruby 3.4.1 (2024-12-25 revision https://github.com/ruby/json/commit/48d4efcb85) +YJIT +PRISM [arm64-darwin24] Warming up -------------------------------------- json (2.10.2) 1.000 i/100ms Calculating ------------------------------------- json (2.10.2) 4.614 (± 0.0%) i/s (216.74 ms/i) - 24.000 in 5.201871s ``` These benchmarks are run via a script ([link](https://gist.github.com/radiospiel/04019402726a28b31616df3d0c17bd1c)) which is based on the gem's `benchmark/encoder.rb` file. There are probably better ways to run benchmarks :) My version allows to combine multiple test cases into a single one. The `dumps` benchmark, which covers the JSON files in `benchmark/data/*.json` – with the exception of `canada.json` – , reported a minor speedup within statistical uncertainty. https://github.com/ruby/json/commit/7d77415108