Simplest Hash Functions

Tiny, stupid, fast

A recent blog post resurfaced on Hacker News arguing for the cheerful minimalism of "stupid" hash functions — the kind you can write on a cocktail napkin and run on a microcontroller. The author sketches tiny variants (think additions, skips, a rotate here and there) and names one implementation "rapidhash." They rate it "AAA" for the scream it will elicit from a cryptographer; it has been reported that the post warns there is no safety guarantee for production use and that adversarial inputs could easily trigger catastrophic collisions and HashDoS.

When the trade-offs make sense

But the post isn't trolling; it's practical. If your inputs are static, vetted, or come from constrained domains (song lyrics, compiler symbols, retrocomputing projects), a pared-down hash can save cycles and energy. Need a hash within 20 ticks? Fine. Want to sample or skip bytes to reduce work? Go ahead. The author even shows experiments: an addition-based hash on blog-paragraph text allegedly produced bit probabilities within ±3% of 50% and tolerable bit correlations, because long, unstructured inputs can camouflage many theoretical flaws.

Caveats and cultural context

This is not a call to ignore standards. The point is pedagogical and economical: stripping hashes to the bare minimum exposes how expensive hash tables really are and nudges you to pick the right data structure instead of concatenating keys like ${x},${y}. Think of it as the "fast-and-loose" cousin of SHA-256 — useful in niche, controlled settings, laughably unsafe in adversarial ones.

The takeaway

So: clever, concise, and occasionally beautiful — but risky. If you're building anything user-facing or exposed to hostile inputs, stick to well-studied hashes. If you're optimizing an embedded device, emulating 1980s hardware, or benchmarking how little you can get away with, these simplest hashes are worth a look. Who knew being economical could also be an act of design?

Sources: purplesyringa.moe, Hacker News