test(p/uint256): add randomize fuzz tests

[jinoosss]

Descriptions

Add comprehensive fuzz tests for uint256 operations to verify correctness through randomized property-based testing.

Changes

New Test Files

Added 6 new test files under contract/r/gnoswap/test/fuzz/:

• uint256_arithmetic_fuzz_params_test.gno - Parameter definitions for arithmetic law tests
• uint256_arithmetic_fuzz_test.gno - Arithmetic property tests (associativity, commutativity, distributivity, identity)
• uint256_fuzz_params_test.gno - Parameter definitions for basic operations
• uint256_fuzz_test.gno - Basic operation tests (Mul, Div, Mod, Add, Sub, overflow checks)
• uint256_math_fuzz_params_test.gno - Parameter definitions for math functions
• uint256_math_fuzz_test.gno - Math function tests (MulDiv, MulDivRoundingUp, DivRoundingUp)

Test Categories

Arithmetic Laws

• Addition/Multiplication associativity and commutativity
• Distributive law: a * (b + c) = a * b + a * c
• Identity laws: a + 0 = a, a * 1 = a, a * 0 = 0
• Subtraction inverse: a - a = 0
• DivMod relation: (a / b) * b + (a % b) = a

Basic Operations

• Mul, MulOverflow
• Div, Mod, DivMod
• Add, AddOverflow
• Sub, SubOverflow

Math Functions

• MulDiv with identity and zero numerator tests
• MulDivRoundingUp with ceiling comparison tests
• DivRoundingUp with exact division and remainder tests

Sparse Multiplication (umul)

• Edge cases: max values, asymmetric operands, zero values, alternating bits
• Commutativity and identity verification

Validation Logic

Each test includes IsValid() predicate functions that accurately predict operation outcomes:

• mulHi() function computes upper 256 bits of 512-bit multiplication for overflow detection
• Overflow/underflow conditions are validated against actual operation results
• Tests panic on invalid states, allowing the fuzz framework to verify prediction accuracy

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud