dnf地下城与勇士:谁能详细讲解一下.gvd格式文件（悬赏分会根据答案的质量增加）

gvd内部首先是64字节的文件头，其中第16个字节处存放字典名称，第40个字节处用3个字节存放(数据块大小+16)，其余字节固定不变。之后就是数据块，在数据块中，首先是2个字节表示单词数量，然后是3个字节表示前缀索引区在数据块中的偏移量，然后是3个字节表示块索引区在数据块中的偏移量，到此为止共72个字节，之后是以下内容：

• 前缀索引区共26*26*5字节，表示的是以a,ab,ac,ad,...zz开头的单词在字典中的位置。每5字节前3个字节表示第一个该前缀的单词在数据块中的偏移量，后2个字节表示单词的序号。

• 块索引区每隔64个单词记录一个位置，每个位置用3个字节表示。假如有n个单词，则该块大小为((n-1)/64+1)*3
  

• 单词区，依次排放按忽略大小写排序的单词，每个单词第1个字节表示该块的大小，后面3个字节表示单词的解释在数据块中的偏移量，后面记录的是单词。单词区结束后跟着两个字节的0xFF

• 解释区， 依次排放每个单词的解释，每个解释以字节0结束
  

Three group velocity dispersion (GVD) compensation schemes, i.e., the post-compensation, precompensation and hybrid-compensation schemes, are discussed with considering polarization mode dispersion (PMD). In the 10- and 40-Gbit/s non-return-zero (NRZ) on-off-key (OOK) systems, three physical factors, Kerr effect, GVD and PMD are considered. The numerical results show that, when the impact of PMD is taken into account, the GVD pre-compensation scheme performs best with more than 1 dB better of average eye-opening penalty (EOP) when input power is up to 10 dBm in the 10-Gbit/s system. However the GVD post-compensation scheme performs best for the case of 40 Gbit/s with input power less than 13 dBm, and GVD pre-compensation will be better if the input power increased beyond this range. The results are different from those already reported under the assumption that the impact of PMD is neglected. Therefore, the research in this paper provide a different insight into the system optimization when PMD, Kerr effect and GVD are considered.