static byte[] byteArrayFromLongs_bigEndian(long[] a) {
  ret byteArrayFromLongs_bigEndian(a, 0, l(a));
}

static byte[] byteArrayFromLongs_bigEndian(long[] a, int from, int to) {
  byte[] b = new byte[(to-from)*8];
  for (int i = 0; i < a.length; i++) {
    long s = a[from+i];
    b[i*8] = (byte) (s >> 56);
    b[i*8+1] = (byte) (s >> 48);
    b[i*8+2] = (byte) (s >> 40);
    b[i*8+3] = (byte) (s >> 32);
    b[i*8+4] = (byte) (s >> 24);
    b[i*8+5] = (byte) (s >> 16);
    b[i*8+6] = (byte) (s >> 8);
    b[i*8+7] = (byte) s;
  }
  ret b;
}

Began life as a copy of #1035892