Correct the FNV-1a 64-bit offset basis and assert known hash outputs

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Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
78/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Active
Tech stack
rust
Domain
compilers, testing-qa

Research direction

Read std/string/hash.wave at the cited initialization and tests/cases/shared/test81.wave at the existing hash check. Run the relevant shared test, then add exact checks for the empty string, a single ASCII byte, and a longer string, verifying the 64-bit bit patterns and intentional modulo-2^64 behavior. Done means the known FNV-1a outputs pass without adding dependencies.

Written by the indexing model from the issue text.

Description

bug good first issue

fnv1a_64 initializes its hash with 1469598103934665603, which differs from the FNV-1a 64-bit offset basis 14695981039346656037 (0xCBF29CE484222325). The empty string already exposes the difference: the loop is skipped, so the function returns the incorrect seed. Nonempty hashes consequently do not interoperate with FNV-1a implementations.

The existing shared/test81 check only requires a nonzero result, which cannot catch a wrong algorithm constant. The correct bit pattern exceeds positive i64, so a fix must also handle unsigned arithmetic/result representation deliberately.

Code evidence:

Acceptance:

  • Use the correct 64-bit offset basis and intentional modulo-2^64 multiplication, preserving the existing public result type unless a separately reviewed API change is needed.
  • Add exact known-output checks for the empty string, a single ASCII byte, and a longer string; compare the 64-bit bit pattern rather than assuming a positive signed result.
  • Keep the implementation dependency-free and note that correcting this bug changes previously computed hashes.

Reference: FNV offset basis values, RFC 9923 section 5. This is a small constant/arithmetic and regression-test contribution.

Audit status: static source inspection against canonical master ea74c2dafc31da876e5561f2d176ba719f5a0458 on 2026-09-10. No compiler build, test execution, implementation change or local reproduction was performed for this report. The examples describe the source-derived behavior to verify when implementing the fix.

Dominant language
Rust
Stars
53
Forks
16
Avg merge
4h 6m
Merged PRs (30d)
44

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