docs: public static long[] truncateI(long[] v, int len) {
      final int zap = (v.length * Long.SIZE) - len;
      final int zapWords = (zap >>> LONG_LOG2_SIZE);
      final int zapbits = zap & LONG_LOG2_MASK;
      Arrays.fill(v, v.length - zapWords, v.length, 0);
      if(zapbits > 0) {
        v[v.length - zapWords - 1] &= (LONG_ALL_BITS >>> zapbits);
      }
      return v;
    }