[ruby-core:121844] [Ruby Feature#21308] Replacing the Float#to_s (dtoa.c) implementation with a modern algorithm

Issue #21308 has been updated by nobu (Nobuyoshi Nakada).


The interface of `fpconv_dtoa()` looks quite different from `dtoa()` in missing/dtoa.c.
Rather `grisu2()` itself is closer?

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Feature #21308: Replacing the Float#to_s (dtoa.c) implementation with a modern algorithm
https://bugs.ruby-lang.org/issues/21308#change-112906

* Author: watson1978 (Shizuo Fujita)
* Status: Open
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This is a feature request to replace Ruby's `Float#to_s` implementation with a modern high-performance float-to-string conversion algorithm such as Grisu.

Currently, `Float#to_s` in Ruby uses the BSD-derived implementation in [missing/dtoa.c](https://github.com/ruby/ruby/blob/master/missing/dtoa.c).
Meanwhile, `json` gem  has adopted a Grisu-based implementation in [ruby/json#768](https://github.com/ruby/json/pull/768), it has been improve the performance of float-to-string conversion dramatically.

It appears to have brought about a 10 times improvement in performance.
However, the improvement is limited to the `json` gem.

If we can use the same implementation in `Float#to_s`, it will introduce the improvement in all float-to-string conversion cases.

(In additional, it would be better if an API could be added that could be called directly from the C extension library, it will reduce the overhead of the call.)



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