[ruby-core:121829] [Ruby Feature#21308] Replacing the Float#to_s (dtoa.c) implementation with a modern algorithm

[ruby-core:121829] [Ruby Feature#21308] Replacing the Float#to_s (dtoa.c) implementation with a modern algorithm

[watson1978 (Shizuo Fujita) via ruby-core]

Issue #21308 has been reported by watson1978 (Shizuo Fujita).

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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

* Author: watson1978 (Shizuo Fujita)
* Status: Open
----------------------------------------
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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[ruby-core:121844] [Ruby Feature#21308] Replacing the Float#to_s (dtoa.c) implementation with a modern algorithm

[nobu (Nobuyoshi Nakada) via ruby-core]

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?

----------------------------------------
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
----------------------------------------
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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[ruby-core:122041] [Ruby Feature#21308] Replacing the Float#to_s (dtoa.c) implementation with a modern algorithm

[radiospiel (Enrico Thierbach) via ruby-core]

Issue #21308 has been updated by radiospiel (Enrico Thierbach).


The change in https://github.com/ruby/json/pull/768 was an easy win, because the previous implementation was calling into question`Float#to_s` via `rb_funcall`. The overhead of doing so is so extreme, that any implementation that would skirt that would show a massive improvement already.

In fact, a first attempt using dtoa.c already showed a 600% or so performance improvement on a clinical example. 

I then decided that maybe this would also be a great moment to look at alternative implementations, since the flexibility provided by dtoa.c is not necessary in the context of the json gem. Other motivational factors have been:

- dtoa generates output right to left (IIRC), but, at least for an integration with the json gem, generating left to right saves a memcpy, which would add a 5-10% overhead;
- more modern algorithms are readily available.

I believe integrating a more modern implementation in the ruby runtime certainly is benefitial, but the gains are not as massive as @watson1978 hopes to achieve here, unfortunately.
 

----------------------------------------
Feature #21308: Replacing the Float#to_s (dtoa.c) implementation with a modern algorithm
https://bugs.ruby-lang.org/issues/21308#change-113190

* Author: watson1978 (Shizuo Fujita)
* Status: Open
----------------------------------------
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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