MurmurHash2 in TypeScript

murmur2.ts

/* eslint-disable no-fallthrough */

// Inspired by: https://github.com/levitation/murmurhash-js

export default function murmur2(data: string, seed: number = 0): number {
  // 'm' and 'r' are mixing constants generated offline.
  // They're not really 'magic', they just happen to work well.

  // const m = 0x5bd1e995;
  // const r = 24;

  let k,
    i = 0,
    len = data.length,
    nBlocks = len >>> 2;

  // Initialize the hash to a 'random' value

  seed ^= len;

  // Mix 4 bytes at a time into the hash

  for (; nBlocks--; ++i) {
    k =
      (data.charCodeAt(i) & 0xff) |
      ((data.charCodeAt(++i) & 0xff) << 8) |
      ((data.charCodeAt(++i) & 0xff) << 16) |
      ((data.charCodeAt(++i) & 0xff) << 24);

    k = /* Math.imul(k, m): */ ((k * 0x5bd1) << 16) + k * 0xe995;
    k ^= /* k >>> r: */ k >>> 24;

    seed =
      /* Math.imul(seed, m): */ (((seed * 0x5bd1) << 16) + seed * 0xe995) ^
      /* Math.imul(k, m): */ (((k * 0x5bd1) << 16) + k * 0xe995);
  }

  // Handle the last few bytes of the input array

  switch (len & 3) {
    case 3:
      seed ^= (data.charCodeAt(i + 2) & 0xff) << 16;
    case 2:
      seed ^= (data.charCodeAt(i + 1) & 0xff) << 8;
    case 1:
      seed ^= data.charCodeAt(i) & 0xff;
      seed = /* Math.imul(seed, m): */ ((seed * 0x5bd1) << 16) + seed * 0xe995;
  }

  // Do a few final mixes of the hash to ensure the last few
  // bytes are well-incorporated.

  seed ^= seed >>> 13;
  seed = /* Math.imul(seed, m): */ ((seed * 0x5bd1) << 16) + seed * 0xe995;

  return (seed ^ (seed >>> 15)) >>> 0;
}