test: migrate stats/base/dists/halfnormal/logpdf to ULP-based assertions

[kgryte]

Resolves a part of #11352.

Description

What is the purpose of this pull request?

This pull request:

• migrates the tests for stats/base/dists/halfnormal/logpdf from relative tolerance testing to ULP difference testing.

Specifically, test/test.logpdf.js, test/test.factory.js, and test/test.native.js are updated to replace the delta/tol computation (previously 40.0 * EPS * abs( expected[ i ] )) with @stdlib/assert/is-almost-same-value, and the now unused @stdlib/math/base/special/abs and @stdlib/constants/float64/eps requires are removed.

The ULP constant used in all three files is 4, which is the measured minimum over the full 1000-case Julia fixture set:

• main.js (JavaScript): maximum observed ULP difference is 4.
• factory.js (JavaScript): maximum observed ULP difference is 4.
• native.js (C): maximum observed ULP difference is 4.

The bound was tightened from a high starting value down to the smallest integer which still passes; at 3 all three files fail two assertions (the worst case being x = 0.2430826624208926, sigma = 0.1403330726611418, where the expected value is 0.23771503646137082 and the returned value is 0.2377150364613707). The full suite was run twice at 4 to confirm the result is deterministic, once with the native add-on built locally so that test.native.js was exercised rather than skipped.

Related Issues

Does this pull request have any related issues?

This pull request has the following related issues:

• [RFC]: Migrate math/base/special packages from relative tolerance testing to ULP difference testing (tracking issue) #11352

Questions

Any questions for reviewers of this pull request?

No.

Other

Any other information relevant to this pull request? This may include screenshots, references, and/or implementation notes.

Only test files are modified; no source, documentation, or benchmark files are touched.

Checklist

Please ensure the following tasks are completed before submitting this pull request.

• Read, understood, and followed the contributing guidelines.

AI Assistance

When authoring the changes proposed in this PR, did you use any kind of AI assistance?

• Yes
• No

If you answered "yes" above, how did you use AI assistance?

• Code generation (e.g., when writing an implementation or fixing a bug)
• Test/benchmark generation
• Documentation (including examples)
• Research and understanding

Disclosure

If you answered "yes" to using AI assistance, please provide a short disclosure indicating how you used AI assistance. This helps reviewers determine how much scrutiny to apply when reviewing your contribution. Example disclosures: "This PR was written primarily by Claude Code." or "I consulted ChatGPT to understand the codebase, but the proposed changes were fully authored manually by myself.".

This PR was authored by Claude Code as part of an automated conversion task. The migration mirrors the idiom established in previously merged conversions (e.g. stats/base/dists/laplace/logpdf), and the ULP bound was determined empirically by measuring the per-fixture ULP difference and verifying that the next smaller bound fails.

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@stdlib-js/reviewers

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Generated by Claude Code

[stdlib-bot]

Coverage Report

Package	Statements	Branches	Functions	Lines
stats/base/dists/halfnormal/logpdf	$\\color{red}305/307$ $\\color{green}+99.35\\%$	$\\color{red}19/20$ $\\color{green}+95.00\\%$	$\\color{green}4/4$ $\\color{green}+100.00\\%$	$\\color{red}305/307$ $\\color{green}+99.35\\%$

The above coverage report was generated for the changes in this PR.