GenerateRandomSearch

Perfect Hash Generator

When the set of keys is known ahead of time and never changes — reserved words, column names, a fixed set of commands — a hash can be found that gives every one of them its own slot. No chains, no probing, no comparison after the lookup beyond confirming the key. The search is a search: try multipliers until one happens to separate every key. For a few dozen keys it usually takes only a handful of tries.

What this generator does

Tries random multipliers and shifts against your key list until one sends every key to a different slot, then shows the parameters and the finished table.

How to use this tool

  1. Paste your keys, one per line.
  2. Search, and read the multiplier and shift that separate them.
  3. Ask for no spare slots if you want the table exactly as large as the list.
  4. Copy the table out to build your lookup.

Understanding the controls

Keys
One per line, from two up to four hundred. Blank lines and repeats are ignored rather than counted, since a repeat is the same key twice.
No spare slots
Makes the table exactly as large as the key list. Such a hash is harder to find and leaves nowhere to add a key later, but wastes no space.

Common use cases

  • A lookup table for a fixed set of keywords or commands
  • Speeding up a parser that keeps comparing strings
  • Building a switch over field names without a chain of comparisons
  • Demonstrating what makes a hash function good or bad
  • A compact table for an embedded target with no room for chains

How this generator works

The hash is the usual multiply-and-mix over the characters, with the multiplier and shift drawn at random until a set of parameters happens to separate every key. Before the result is shown, every key is hashed again from the stored parameters and checked for a repeat, checked against the slot the table claims, and checked to be inside the table at all.

Randomness and fairness

The multiplier and shift come from the browser's secure generator, so searching twice with the same keys usually gives different parameters. Both are equally valid.

For how randomness is produced across the whole site, see how Generate Random works.

Limitations and good to know

  • It only holds for the exact key list given. Add a key and the hash may collide, so it must be found again.
  • Keys are read as text and compared exactly, including case and spacing.
  • The search is random rather than clever, so a very long list with no spare slots may not settle.
  • The hash shown is a simple multiply-and-mix, not a cryptographic one, and must not be used where a hash needs to resist attack.

Privacy and your data

Your keys never leave your browser: the search runs on the page and nothing is transmitted or stored.

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