What is the djb2 hash?

djb2 is a very simple string hash by Daniel J. Bernstein. It starts from the magic constant 5381 and, for each byte, computes hash = hash * 33 + byte. It is fast and surprisingly well-distributed for its size.

Why does djb2 start at 5381?

5381 is the empirically chosen seed Bernstein found gave good distribution. Combined with the multiplier 33, it spreads typical ASCII strings across the 32-bit space with few collisions.

What is the xor variant?

The xor variant (sometimes called djb2a) replaces the addition with XOR, computing hash = hash * 33 ^ byte. It behaves similarly but mixes bits slightly differently; this tool shows both.

Why is multiply-by-33 written as a shift and add?

Classic implementations use ((hash << 5) + hash) because that equals hash * 33 and was faster on older CPUs. The result is identical to a direct multiply by 33.

No. djb2 is a non-cryptographic hash that is trivial to collide deliberately. Use it for hash tables and lightweight fingerprints, never for passwords, tokens or signatures.

djb2 Hash Calculator

Q: Is djb2 secure?

No. djb2 is a non-cryptographic hash that is trivial to collide deliberately. Use it for hash tables and lightweight fingerprints, never for passwords, tokens or signatures.

djb2 is a classic string hash by Daniel J. Bernstein, famous for being tiny yet effective. It appears in countless C codebases and tutorials as the go-to example of a simple hash. This calculator computes both the standard and xor variants of djb2 in your browser.

How it works

djb2 keeps a single 32-bit accumulator:

Initialise hash = 5381.
For each byte c, update hash = hash * 33 + c. Many implementations write the multiply as ((hash << 5) + hash), which equals hash * 33.
The 32-bit accumulator after the last byte is the hash.

The xor variant is identical except step 2 uses hash = hash * 33 ^ c, replacing the addition with a bitwise XOR.

Example

Hashing the string hello with the classic add variant gives 261238937 (decimal), which is 0x0f923099 in hex. The xor variant produces a different value for the same input.

Notes

Both variants are computed with a correct 32-bit overflow multiply so results match reference C code. The choice of 5381 and 33 is empirical, not derived — they simply distribute real-world strings well. djb2 has no cryptographic strength; keep it to hash tables and quick fingerprints. All computation is local.