fix broken pow

[thedavidmeister]

Motivation

Solution

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Summary by CodeRabbit

• New Features

  • No user-facing features added.

• Bug Fixes

  • Improved stability in power-related decimal operations by adding a safeguard to prevent overflow in rare high-scale scenarios.

• Tests

  • Added a new case covering large coefficients with negative exponents in power calculations.

• Chores

  • Updated benchmark and gas snapshots, reflecting revised performance metrics across multiple DecimalFloat operations.

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Pre-merge checks and finishing touches

✅ 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 “fix broken pow” directly references the key functional change of adding a guard and test coverage around the pow implementation, concisely summarizing the primary intent of the pull request.
Docstring Coverage	✅ Passed	No functions found in the changes. Docstring coverage check skipped.

✨ Finishing touches

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📜 Recent review details

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📥 Commits

Reviewing files that changed from the base of the PR and between 47fde80 and 3787a68.

📒 Files selected for processing (3)

• .gas-snapshot (5 hunks)
• src/lib/implementation/LibDecimalFloatImplementation.sol (1 hunks)
• test/src/lib/LibDecimalFloat.pow.t.sol (1 hunks)

🧰 Additional context used

🧠 Learnings (10)

📚 Learning: 2025-09-09T15:11:31.003Z

Learnt from: thedavidmeister
PR: rainlanguage/rain.math.float#130
File: src/lib/implementation/LibDecimalFloatImplementation.sol:320-330
Timestamp: 2025-09-09T15:11:31.003Z
Learning: In LibDecimalFloatImplementation.sol div function, returning zero when underflowExponentBy > 76 is intentional "non-error underflow" behavior rather than reverting. This graceful handling is the main goal of the changes.

Applied to files:

• src/lib/implementation/LibDecimalFloatImplementation.sol

📚 Learning: 2025-09-30T15:09:39.446Z

Learnt from: thedavidmeister
PR: rainlanguage/rain.math.float#144
File: src/lib/parse/LibParseDecimalFloat.sol:88-111
Timestamp: 2025-09-30T15:09:39.446Z
Learning: In src/lib/parse/LibParseDecimalFloat.sol, the fractional rescaling path (around lines 88-111) executes at most once per parseDecimalFloatInline call within an if-else branch, not in a loop, so there are no repeated 10**scale operations to optimize with a lookup table.

Applied to files:

• src/lib/implementation/LibDecimalFloatImplementation.sol

📚 Learning: 2025-09-28T13:28:35.814Z

Learnt from: thedavidmeister
PR: rainlanguage/rain.math.float#144
File: test/src/lib/LibDecimalFloat.pow.t.sol:40-61
Timestamp: 2025-09-28T13:28:35.814Z
Learning: In test/src/lib/LibDecimalFloat.pow.t.sol, the diffLimit tolerance (currently 8.6%) represents a conservative worst-case bound to accommodate precision limitations of table lookup interpolation for fractional exponents in the pow function. The exponentiation-by-squaring approach used for integer parts achieves much tighter precision, but the tolerance must account for the less precise table-based calculations used for fractional exponents.

Applied to files:

• src/lib/implementation/LibDecimalFloatImplementation.sol
• test/src/lib/LibDecimalFloat.pow.t.sol
• .gas-snapshot

📚 Learning: 2025-09-30T20:11:57.768Z

Learnt from: thedavidmeister
PR: rainlanguage/rain.math.float#144
File: src/lib/implementation/LibDecimalFloatImplementation.sol:708-732
Timestamp: 2025-09-30T20:11:57.768Z
Learning: In src/lib/implementation/LibDecimalFloatImplementation.sol, the `lookupLogTableVal` internal function intentionally omits bounds checking for gas optimization because all calling functions perform the necessary validation before invocation (e.g., checking against LOG_MANTISSA_LAST_INDEX in log10).

Applied to files:

• src/lib/implementation/LibDecimalFloatImplementation.sol
• .gas-snapshot

📚 Learning: 2025-09-28T12:52:45.815Z

Learnt from: thedavidmeister
PR: rainlanguage/rain.math.float#144
File: src/lib/LibDecimalFloat.sol:671-686
Timestamp: 2025-09-28T12:52:45.815Z
Learning: In LibDecimalFloat.sol, the pow function has always rejected negative bases and reverted with an error. Prior to recent changes, it used a different error type, but the fundamental policy of not allowing negative bases (except when b == 0) has been consistently maintained across the codebase's history.

Applied to files:

• src/lib/implementation/LibDecimalFloatImplementation.sol
• test/src/lib/LibDecimalFloat.pow.t.sol

📚 Learning: 2025-08-29T10:38:26.353Z

Learnt from: thedavidmeister
PR: rainlanguage/rain.math.float#115
File: src/lib/implementation/LibDecimalFloatImplementation.sol:593-601
Timestamp: 2025-08-29T10:38:26.353Z
Learning: In Solidity, int256(1) when passed through the maximize function in LibDecimalFloatImplementation.sol produces exactly (1e76, -76), not an approximation. This means the special case for signedCoefficient == 1e76 in log10 correctly handles powers of 10 like log10(1).

Applied to files:

• src/lib/implementation/LibDecimalFloatImplementation.sol

📚 Learning: 2025-08-29T10:38:26.353Z

Learnt from: thedavidmeister
PR: rainlanguage/rain.math.float#115
File: src/lib/implementation/LibDecimalFloatImplementation.sol:593-601
Timestamp: 2025-08-29T10:38:26.353Z
Learning: The maximize function in LibDecimalFloatImplementation.sol produces exact results for simple integer values like 1. maximize(1, 0) yields exactly (1e76, -76) with no precision loss, and the log10 special case for signedCoefficient == 1e76 correctly handles this.

Applied to files:

• src/lib/implementation/LibDecimalFloatImplementation.sol

📚 Learning: 2025-09-10T19:20:35.927Z

Learnt from: thedavidmeister
PR: rainlanguage/rain.math.float#135
File: test/src/lib/LibDecimalFloat.pow.t.sol:160-161
Timestamp: 2025-09-10T19:20:35.927Z
Learning: In test/src/lib/LibDecimalFloat.pow.t.sol, the comment "we do not try" in the context of "The round trip should not error so we do not try" refers to not using try/catch constructs around the powExternal call, contrasting with previous versions that used nested try/catch blocks.

Applied to files:

• test/src/lib/LibDecimalFloat.pow.t.sol

📚 Learning: 2025-08-21T18:03:40.347Z

Learnt from: thedavidmeister
PR: rainlanguage/rain.math.float#107
File: test/lib/LibDecimalFloatSlow.sol:37-45
Timestamp: 2025-08-21T18:03:40.347Z
Learning: In test/lib/LibDecimalFloatSlow.sol, the "slow" implementation is intentionally different from the production implementation to serve as an independent reference for fuzzing tests. The goal is to have two different approaches (expensive loops vs optimized jumps) that produce equivalent results, not identical implementations.

Applied to files:

• .gas-snapshot

📚 Learning: 2025-08-29T14:54:24.240Z

Learnt from: thedavidmeister
PR: rainlanguage/rain.math.float#115
File: test/src/lib/LibDecimalFloat.decimal.t.sol:122-126
Timestamp: 2025-08-29T14:54:24.240Z
Learning: In test/src/lib/LibDecimalFloat.decimal.t.sol, the fromFixedDecimalLossy function converts uint256(type(int256).max) losslessly because the boundary check is `value > uint256(type(int256).max)`, not `>=`. Values exactly equal to type(int256).max still take the lossless conversion path.

Applied to files:

• .gas-snapshot

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🔇 Additional comments (2)

src/lib/implementation/LibDecimalFloatImplementation.sol (1)

891-895: Overflow guard keeps interpolation safe

Nice catch on the idx > 4 && scale == 1e76 path—scaling both scale and mantissaCoefficient by 1/10 pulls idx * scale back under the int256 ceiling while preserving the relative position for interpolation. This should eliminate the overflow without disturbing accuracy.

test/src/lib/LibDecimalFloat.pow.t.sol (1)

73-73: Regression case looks great

This extra checkPow hits the high-magnitude/negative-exponent combo that exposed the overflow, so we’ll keep coverage on the fix going forward.

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