Skip to content

Fix: Math:gen_rngのseedにnumを与え、options.algorithmにchacha20を指定した或いは何も指定しなかった場合、seed & 255を内部的にseedとしてしまう問題を修正。 #1019

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom
Open
MineCake147E wants to merge 8 commits into
base: master
Choose a base branch
from
Open

Fix: Math:gen_rngのseedにnumを与え、options.algorithmにchacha20を指定した或いは何も指定しなかった場合、seed & 255を内部的にseedとしてしまう問題を修正。 #1019

MineCake147E wants to merge 8 commits into from
+47 −9

Conversation

@MineCake147E
Copy link
Contributor

@MineCake147E MineCake147E commented Dec 28, 2025

What

#731 を実装した際、Float64ArrayをUint8Array() constructorの第一引数に指定した場合の仕様の理解が間違っており、numで与えられたシード値が意図せず& 255されてしまっていました。
本修正では、TypedArray.prototype.bufferを取る事により、#731 の実装時に意図したように、numberの内部表現をそのままseedとして使用することにより、3.0と3.0000000000000004で異なる出力を得られるようになります。
これにより、全く同じseedでも、修正前と修正後で出力が変わります。
また、本修正後も旧来の動作を再現できるよう、関数Math:gen_rngのoptions.chacha20NumberSeedLegacyBehaviour(デフォルト:false)にtrueを指定した場合、修正前の動作をする機能を追加しました。

<: (Math:gen_rng(0)(0, 4503599627370495)).to_hex()
<: (Math:gen_rng(0.000001)(0, 4503599627370495)).to_hex()
<: (Math:gen_rng(256.000001)(0, 4503599627370495)).to_hex()

Before:

"b3f8c68b3d7e0"
"b3f8c68b3d7e0"
"b3f8c68b3d7e0"
(null)

After:

"53b92953000f2"
"29f33b8f9931b"
"1ed54e7a15574"
(null)

Why

某Playの出力が複数日連続で同一となった事により発覚。
algorithmにrc4を指定した場合と挙動が大きく異なるため。

Additional info (optional)

Workaround for versions before this fix

  • seedを与える前に.to_str()等でstringに変換する

@codecov-commenter
Copy link

codecov-commenter commented Dec 28, 2025 •
edited
Loading

⚠️ Please install the 'codecov app svg image' to ensure uploads and comments are reliably processed by Codecov.

Codecov Report

❌ Patch coverage is 81.81818% with 2 lines in your changes missing coverage. Please review.

Files with missing lines Patch % Lines
src/utils/random/genrng.ts 80.00% 2 Missing ⚠️
❗ Your organization needs to install the Codecov GitHub app to enable full functionality.
Files with missing lines Coverage Δ
src/interpreter/lib/math.ts 64.64% <100.00%> (ø)
src/utils/random/genrng.ts 57.44% <80.00%> (+5.36%) ⬆️

... and 29 files with indirect coverage changes

🚀 New features to boost your workflow:
  • ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
  • 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

takejohn
takejohn requested changes Jan 12, 2026
View reviewed changes
takejohn
takejohn reviewed Jan 12, 2026
View reviewed changes
@MineCake147E MineCake147E requested a review from takejohn January 13, 2026 08:35
takejohn
takejohn requested changes Jan 13, 2026
View reviewed changes
@MineCake147E @takejohn
Update unreleased/chacha20-seed-unexpected-rounding-fix.md
0447b04 
Co-authored-by: Take-John <takejohn@takejohn.jp>
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment

Reviewers

@takejohn takejohn takejohn requested changes

Assignees

No one assigned

Labels

None yet

Projects

None yet

Milestone

No milestone

Development

Successfully merging this pull request may close these issues.

3 participants

@MineCake147E @codecov-commenter @takejohn