_bigint helpers #11

youknowone · 2026-01-11T12:23:36Z

Summary by CodeRabbit

New Features
- Extended math module with arbitrary-precision versions of standard mathematical operations through an optional feature gate.
Documentation
- Added compatibility guidance note documenting the library's alignment with Python's math module interface.
Refactor
- Improved internal module organization and dependencies.

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coderabbitai · 2026-01-11T12:23:45Z

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📥 Commits

Reviewing files that changed from the base of the PR and between aa6112d and ab02686.

📒 Files selected for processing (4)

README.md
src/math.rs
src/math/bigint.rs
src/math/integer.rs

📝 Walkthrough

Walkthrough

This pull request adds BigInt-based mathematical utilities to RustPython's math module, including functions for permutation, combination, and logarithm calculations. New functions are gated behind a "_bigint" feature flag. Documentation is updated with a compatibility note. Integration changes to existing modules are also introduced.

Changes

Cohort / File(s)	Summary
Documentation `README.md`	Added "Important Note" section clarifying library compatibility with Python's math module but not mathematical correctness
Module and API Exposure `src/math.rs`	Conditionally compiles and re-exports new bigint module and functions (`comb_bigint`, `ldexp_bigint`, `log_bigint`, `log2_bigint`, `log10_bigint`, `perm_bigint`) when "_bigint" feature is enabled
BigInt Implementation `src/math/bigint.rs`	New module providing 6 BigInt-based mathematical functions with divide-and-conquer algorithms for permutation/combination, logarithm calculations with frexp-like fallback for large values, and ldexp with overflow/underflow handling; includes comprehensive tests with property-based testing against Python math results
Module Integration `src/math/integer.rs`	Visibility change: `perm_comb_small` elevated from private to `pub(super)`; removed unused internal `perm_comb` helper function; updated imports to reference `super::bigint`

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~45 minutes

Poem

🐰 A BigInt feast we celebrate today,
With logarithms dancing in every way,
Permutations and combinations bloom,
While Python's math finds new room,
Our burrow of numbers grows!

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title '_bigint helpers' directly references the main feature being introduced: a new internal _bigint module with helper functions (comb_bigint, ldexp_bigint, log_bigint, log2_bigint, log10_bigint, perm_bigint).
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

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coderabbitai

Actionable comments posted: 1

🤖 Fix all issues with AI agents

In @src/math/bigint.rs:
- Around line 104-133: In log_bigint replace the direct f64 .ln() calls with the
CPython-wrapper functions: call crate::m::log(x) instead of x.ln() when
computing log_n (after frexp_bigint returns x) and use crate::m::log(b) (or
crate::m::log(b) for the base) instead of b.ln() in the base-division branch;
update references inside the log_bigint function so log_n is computed via
crate::m::log(x) + std::f64::consts::LN_2 * (e as f64) and the final value is
divided by crate::m::log(b).

📜 Review details

Configuration used: defaults

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between f95c66d and aa6112d.

📒 Files selected for processing (4)

README.md
src/math.rs
src/math/bigint.rs
src/math/integer.rs

🧰 Additional context used

📓 Path-based instructions (3)

src/math/**/*.rs

📄 CodeRabbit inference engine (AGENTS.md)

src/math/**/*.rs: Use existing CPython helper equivalents: FUNC1 → math_1(x, func, can_overflow), FUNC2 → math_2(x, y, func), m_log/m_log10/m_log2 in exponential.rs. If CPython uses a helper, use the corresponding Rust helper.
Use crate::mul_add(a, b, c) instead of a * b + c for expressions of the form a * b + c or c + a * b to match CPython's FMA (fused multiply-add) behavior on platforms like macOS where it's enabled.

Files:

src/math/bigint.rs
src/math/integer.rs

src/**/*.rs

📄 CodeRabbit inference engine (AGENTS.md)

Error handling: Return Result directly with Err(crate::Error::EDOM) or Err(crate::Error::ERANGE) instead of using set_errno. Only valid set_errno call is set_errno(0) to clear errno before libm calls.

Files:

src/math/bigint.rs
src/math.rs
src/math/integer.rs

src/math.rs

📄 CodeRabbit inference engine (AGENTS.md)

Create missing helpers if CPython has a helper we don't have yet, such as math_1_fn for Rust function pointers or special case handlers for specific functions.

Files:

src/math.rs

🧠 Learnings (11)

📓 Common learnings

Learnt from: CR
Repo: RustPython/pymath PR: 0
File: AGENTS.md:0-0
Timestamp: 2026-01-10T13:40:01.981Z
Learning: Applies to src/math/**/*.rs : Use existing CPython helper equivalents: FUNC1 → math_1(x, func, can_overflow), FUNC2 → math_2(x, y, func), m_log/m_log10/m_log2 in exponential.rs. If CPython uses a helper, use the corresponding Rust helper.

Learnt from: CR
Repo: RustPython/pymath PR: 0
File: AGENTS.md:0-0
Timestamp: 2026-01-10T13:40:01.981Z
Learning: Applies to src/math.rs : Create missing helpers if CPython has a helper we don't have yet, such as math_1_fn for Rust function pointers or special case handlers for specific functions.

Learnt from: CR
Repo: RustPython/pymath PR: 0
File: AGENTS.md:0-0
Timestamp: 2026-01-10T13:40:01.981Z
Learning: Applies to src/cmath/**/*.rs : Use mul_add in cmath functions for expressions like 1.0 + x * x, cross-product calculations (mul_add(s1.re, s2.im, -(s2.re * s1.im))), and squared terms to achieve bit-exact matching with CPython.