murmur2.js

const encoder = new TextEncoder()

// bufferLength must be a multiple of 4 to satisfy Int32Array constraints
let bufferLength = 2 * 1024
let buffer = new ArrayBuffer(bufferLength)
let uint8View = new Uint8Array(buffer)
let int32View = new Int32Array(buffer)

export function murmur2(str) {
  if (str.length > bufferLength) {
    // buffer.resize() is only available in recent browsers, so we re-allocate
    // a new and views
    bufferLength = str.length + (4 - str.length % 4)
    buffer = new ArrayBuffer(bufferLength)

    uint8View = new Uint8Array(buffer)
    int32View = new Int32Array(buffer)
  }

  const length = encoder.encodeInto(str, uint8View).written;

  // '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;

  // Initialize the hash
  let h = 0

  // Mix 4 bytes at a time into the hash

  let i = 0
  let len = length
  for (; len >= 4; i++, len -= 4) {
    let k = int32View[i]

    k = Math.imul(k, m)
    k ^= k >>> r
    k = Math.imul(k, m)

    h = Math.imul(h, m)
    h ^= k
  }

  // Handle the last few bytes of the input array

  switch (len) {
    case 3:
      h ^= (uint8View[i * 4 + 2] & 0xff) << 16
    case 2:
      h ^= (uint8View[i * 4 + 1] & 0xff) << 8
    case 1:
      h ^= uint8View[i * 4] & 0xff
      h = Math.imul(h, m)
  }

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

  h ^= h >>> 13
  h = Math.imul(h, m)
  h = (h ^ (h >>> 15)) >>> 0

  return h.toString(36)
}