The rapidhash algorithm is notable for being general purpose, with unusually low latency relative to its quality metrics. Classic algorithms are severely broke

The rapidhash algorithm is notable for being general purpose, with unusually low latency relative to its quality metrics. Classic algorithms are severely broken for many trivial key sets and therefore are not general purpose. However, they may work great for your specific key set and this is something you can test for if you know the properties of your key set. The point of a general purpose hash function is that you can use it with unknown or unknowable key distributions with some degree of assurance that the distribution of hashes is unlikely to be biased in some way. Something else to keep in mind is that those old algorithms are really slow. Modern algorithms explicitly take advantage of the parallelism and width of modern CPU cores. Larger internal hash state allows higher throughput and quality but also increases latency and I-cache footprint, so there is a tension in the design. As I mentioned in another post, if the properties of your key set are well-defined and bounded, it can often make sense to design a hash function that is only high-performance and high-quality for that key set. Most people don’t know how to do this effectively so they mostly stick with general-purpose hash functions, one latency-optimized and one throughput-optimized.