fix(math): correct Math.acosh for large finite inputs

[HiteshShonak]

This Pull Request fixes/closes #5229.

It changes the following:

• When the input is finite and greater than 1/√f64::EPSILON (67_108_864.0), fall back to n.ln() + LN_2 instead of calling f64::acosh() directly, avoiding an internal x² overflow that produces Infinity. Threshold follows the Boost math library convention.
• Add regression tests for Math.acosh(1e308) and Math.acosh(Number.MAX_VALUE).

Testing:

cargo test -p boa_engine math -- --nocapture

Spec reference: https://tc39.es/ecma262/#sec-math.acosh

[Copilot]

Pull request overview

This PR fixes Math.acosh returning Infinity for very large finite inputs by avoiding an overflow inside Rust’s f64::acosh() implementation, and adds regression tests to cover the affected cases.

Changes:

• Add a large-input fast path in Math.acosh for finite n > 1e154 using ln(n) + LN_2.
• Add regression tests for Math.acosh(1e308) and Math.acosh(Number.MAX_VALUE).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
core/engine/src/builtins/math/mod.rs	Adds a large-finite-input fallback to avoid f64::acosh() overflow.
core/engine/src/builtins/math/tests.rs	Adds regression coverage for large finite inputs that previously produced Infinity.

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[github-actions]

Test262 conformance changes

Test result	main count	PR count	difference
Total	52,963	52,963	0
Passed	50,545	50,545	0
Ignored	1,426	1,426	0
Failed	992	992	0
Panics	2	2	0
Conformance	95.43%	95.43%	0.00%

Tested main commit: 66a1cd268ce6006918032b5d0f98d3a63c81b188
Tested PR commit: 6efedce72fce1a7976c19fba9cdb4f8f38950b9e
Compare commits: 66a1cd2...6efedce

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 59.84%. Comparing base (6ddc2b4) to head (6efedce).
⚠️ Report is 917 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #5230       +/-   ##
===========================================
+ Coverage   47.24%   59.84%   +12.60%     
===========================================
  Files         476      582      +106     
  Lines       46892    63459    +16567     
===========================================
+ Hits        22154    37979    +15825     
- Misses      24738    25480      +742     

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[jedel1043]

Would it be better to follow the bounds established by the Boost library?
https://www.boost.org/doc/libs/latest/libs/math/doc/html/math_toolkit/inv_hyper/acosh.html

It documents that the ln approximation is valid for numbers bigger than 1/√epsilon

[HiteshShonak]

Would it be better to follow the bounds established by the Boost library? https://www.boost.org/doc/libs/latest/libs/math/doc/html/math_toolkit/inv_hyper/acosh.html

It documents that the ln approximation is valid for numbers bigger than 1/√epsilon

updated to use 1/sqrt(epsilon) matching the Boost threshold, thanks for the reference

[jedel1043]

Looks great! Thanks!