[pralav-25]

modular_exponential(7, 0, 1) returns 1, while Python's pow(7, 0, 1) returns 0. The zero-exponent identity also needs reduction for negative moduli, which the existing loop otherwise supports.

Initialize the result as 1 % mod and document the nonzero modulus domain. Add a built-in pow oracle across signed bases, zero/positive exponents, and positive/negative moduli, plus a zero-modulus regression.

Validation: 721 tests pass; 480 documentation examples pass (one existing skip); repository Ruff checks pass.

Prepared with AI assistance and verified locally against the stated oracles.

Summary by CodeRabbit

• Bug Fixes

  • Modular exponentiation now matches Python’s pow behavior for positive and negative nonzero moduli, including when the exponent is zero.
  • Using a zero modulus with an exponent of zero continues to raise ZeroDivisionError.

• Tests

  • Added coverage comparing results with Python’s pow across selected bases, exponents, and moduli.

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⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Advanced

Run ID: 35a37b93-a2ec-4893-b8d6-7aa2853b828d

📥 Commits

Reviewing files that changed from the base of the PR and between bd1d152 and 840e0ea.

📒 Files selected for processing (2)

• algorithms/math/modular_exponential.py
• tests/test_modular_exponential_boundaries.py

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📝 Walkthrough

Walkthrough

The modular exponential function now initializes its result as 1 % mod and documents that the modulus must be nonzero. New tests compare selected cases with Python’s three-argument pow and check the zero-modulus exception.

Changes

Modular exponential behavior

Layer / File(s)	Summary
Normalize results and test boundaries algorithms/math/modular_exponential.py, tests/test_modular_exponential_boundaries.py	The function starts with 1 % mod, and its documentation specifies nonzero positive or negative moduli. Tests compare selected inputs with pow and check that modulus zero raises ZeroDivisionError.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix

Merge Risk: ⚪ Minimal · up to 840e0

The change aligns the zero-exponent result with Python’s modular pow behavior for nonzero moduli and tests the zero-modulus exception. No concrete merge-blocking risk is evident.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 33.33% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 3 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: correcting the zero-exponent result for unit and negative moduli.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create a new PR

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