文件CRC计算工具代码，可对目录下所有文件进行计算，计算结果保存在文件中。同时使用内存映射文件加快文件处理速度.可作为工具使用.-File CRC code calculation tools, all the files directory can be calculated, the results stored in the file. Also uses memory mapped files to speed up file processing. Can be used as too