fix: avoid overflow in stats/base/dists/wald/logpdf

[Planeshifter]

Description

What is the purpose of this pull request?

This pull request:

• provides follow-up fixes for commits merged to develop between 2026-08-18 17:33 PDT (fd16a2f) and 2026-08-19 05:08 PDT (dd78acd). An automated review of the 25 commits in that window (style-guide compliance audit plus two independent bug scans over the union diff) surfaced one validated, high-signal issue.

stats/base/dists/wald/logpdf

• Fixes a numerical overflow in 47b5192: the exponent term (lambda*v*v)/(mu*mu*x) overflows before dividing, so logpdf(1.0, 1e155, 1.0) returns NaN and logpdf(1e155, 1.0, 1.0) returns -Infinity instead of finite values, violating the documented NaN-only-on-invalid-input contract. Reassociated as ((lambda/x)*(v/mu))*(v/mu) in lib/main.js:97, lib/factory.js:83, and src/main.c:57; all 100 Julia fixtures still pass at 2 ULP.

Related Issues

Does this pull request have any related issues?

No.

Questions

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No.

Other

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Validation performed on the commit window:

• Style-guide compliance audit (two independent passes) of all changed code against docs/style-guides and established reference packages (e.g., the new stats/base/dists/wald/* packages against stats/base/dists/wald/cdf and stats/base/dists/lognormal/*): no violations found.
• Bug scan (two independent passes) of the union diff: verified the Wald quantile/logcdf/logpdf/stdev formulas and documented example values numerically, JS↔C parity, and the fromIndex index-resolution logic in blas/ext/base/ndarray/dfirst-index-less-than. Only the overflow above survived validation.
• Deliberately excluded: subjective concerns, style preferences not required by the style guides, and anything requiring changes outside the window's diff to validate.

The fix was verified by reproducing the failure on the shipped code, re-running the reassociated implementation, and confirming all 100 Julia fixture cases pass at the tests' 2-ULP tolerance for both logpdf and logpdf.factory.

Checklist

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• Read, understood, and followed the contributing guidelines.

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This PR was produced by a scheduled automated commit-review run using Claude Code: agents reviewed the last 24 hours of commits merged to develop, and the fix in this PR was generated and validated by Claude Code. A human maintainer will audit before marking ready for review.

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Generated by Claude Code

[stdlib-bot]

Coverage Report

Package	Statements	Branches	Functions	Lines
stats/base/dists/wald/logpdf	$\\color{green}327/327$ $\\color{green}+100.00\\%$	$\\color{green}33/33$ $\\color{green}+100.00\\%$	$\\color{green}4/4$ $\\color{green}+100.00\\%$	$\\color{green}327/327$ $\\color{green}+100.00\\%$

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