JavaScript implementation of java.util.UUID's stringify

java-util-uuid-string.js

// https://stackoverflow.com/questions/75387792/javascript-equivalent-of-javas-uuid-class/76967385#76967385

// assume x under range of signed long value
function unsignedBitShiftRight(x, n) {
  if (n === 0) { return x; }
  else if (x >= 0) { return x >> n; }
  // convert to two's complement and then do the shifting
  else { return (((1n << 64n) - 1n) ^ (- (x + 1n))) >> n; }
}

// lsb & msb are both BigInt
// lsb & msb taken from Java's getLeastSignificantBits & getMostSignificantBits
function toUuidString(lsb, msb) {
  return `${
    digits(unsignedBitShiftRight(msb, 32n), 8n)}-${
    digits(unsignedBitShiftRight(msb, 16n), 4n)}-${
    digits(msb, 4n)}-${
    digits(unsignedBitShiftRight(lsb, 48n), 4n)}-${
    digits(lsb, 12n)}`
}

function digits(value, ds) {
  const hi = 1n << (ds * 4n)
  return (hi | (value & (hi - 1n))).toString(16).slice(1)
}