hadoop - 了解 Hadoop VIntWritable 压缩

Question

我知道这有点丢人，但我不了解 VIntWritable 和 VLongWritable 中的压缩技术。有人可以详细说明 WritableUtils.java 中的示例
代码片段吗

 public static void writeVLong(DataOutput stream, long i) throws IOException {
    if (i >= -112 && i <= 127) {
      stream.writeByte((byte)i);
      return;
    }

    int len = -112;
    if (i < 0) {
      i ^= -1L; // take one's complement'
      len = -120;
    }

    long tmp = i;
    while (tmp != 0) {
      tmp = tmp >> 8;
      len--;
    }

    stream.writeByte((byte)len);

    len = (len < -120) ? -(len + 120) : -(len + 112);

    for (int idx = len; idx != 0; idx--) {
      int shiftbits = (idx - 1) * 8;
      long mask = 0xFFL << shiftbits;
      stream.writeByte((byte)((i & mask) >> shiftbits));
    }
  }