The recent introduction of Rain, a new non-cryptographic hash function, has sparked an interesting debate within the developer community about the role and necessity of cryptographic-ish hash functions in modern software development. While Rain boasts impressive performance metrics as the fastest 128-bit and 256-bit non-cryptographic hash function, the discussion reveals deeper questions about hash function design and implementation choices.
Key Features of Rain:
- Fastest 128-bit and 256-bit non-cryptographic hash
- Under 140 lines of code
- Passes all SMHasher3 tests
- Supports multiple output sizes: 64, 128, and 256 bits
- Prime-based mixing function for strong avalanche properties
Performance vs. Security Trade-offs
The community discussion highlights a fundamental question about hash function design: what's the value proposition of a hash function that sits between fully cryptographic and purely non-cryptographic implementations? Several developers point out that while cryptographic hashes are computationally more expensive, they're often fast enough for most applications. However, others argue that there are specific use cases where performance-optimized non-cryptographic hashes make sense.
Real-world Applications
One particularly insightful comment from the community explains practical applications:
There are applications where hashes are used as identifiers, where it would be impossible to use the original data to resolve possible collisions. One example would be in RTTI (Run Time Type Information), when you want to check if two objects are instances of the same type... If there is a collision, then the program behavior is undefined, so it is ideal to minimize probability of collision.
Technical Innovation
Rain's development process reveals interesting insights into hash function design. The function uses carefully selected prime numbers based on their avalanche qualities under multiply modulo operations. This selection process required several days of computation on modern hardware to identify primes that provided optimal bit-flip probability across the widest possible range of bits.
Benchmark Controversy
The community has raised concerns about the validity of the published benchmarks, particularly noting that the current measurements appear to be dominated by startup time rather than actual hash computation. This highlights the importance of proper benchmark methodology in evaluating hash function performance.
Performance Comparison (C++ vs WASM):
- C++ implementation consistently outperforms WASM
- Performance gap ranges from 4x to 23x faster
- Largest performance difference observed with 1,000,000 byte input (23x)
- Smallest performance difference with 100,000,000 byte input (4x)
Future Considerations
The discussion reveals ongoing debates about hash function selection in major projects, including Git's content-addressable storage system and programming language implementations. While Rain shows promise in certain applications, the community emphasizes the importance of choosing the right tool for specific use cases rather than adopting a one-size-fits-all approach.
Reference: Rain: A Fast, General-Purpose Non-Cryptographic Hash Function