# `ExDataSketch.DataSketches.Murmur3`
[🔗](https://github.com/thanos/ex_data_sketch/blob/main/lib/ex_data_sketch/data_sketches/murmur3.ex#L1)

Minimal MurmurHash3_x64_128 implementation for DataSketches seed hash computation.

This module implements only the subset of MurmurHash3 needed to compute the
16-bit seed hash used by Apache DataSketches for compatibility verification.
The seed hash identifies which hash function/seed was used to create a sketch,
preventing merges between incompatible sketches.

## Seed Hash Computation

The seed hash is computed as:
1. Hash the 8-byte little-endian encoding of the seed using MurmurHash3_x64_128
   with hash seed 0.
2. Take the lower 16 bits of the first 64-bit output word.

For the default DataSketches seed of 9001, this produces a fixed constant.

# `seed_hash`

```elixir
@spec seed_hash(non_neg_integer()) :: non_neg_integer()
```

Computes the DataSketches seed hash for a given seed value.

Returns a 16-bit unsigned integer matching the value produced by
`org.apache.datasketches.common.Util.computeSeedHash(seed)` in Java.
The computation hashes the seed as a little-endian u64 using MurmurHash3_x64_128
with hash seed 0, then takes the lower 16 bits of the first output word.

## Examples

    iex> h = ExDataSketch.DataSketches.Murmur3.seed_hash(9001)
    iex> is_integer(h) and h >= 0 and h <= 0xFFFF
    true

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*Consult [api-reference.md](api-reference.md) for complete listing*