#7zx official archive

That 'testing' is faster implies that at least one step, most likely writing data to disk, is skipped.

#7zx official archive

I strongly expect that this is the way it works, because writing everything to disk simply to test an archive seems insane and would be no faster than a 'real' decompression of the data. You follow exactly the same steps as you would for decompression, but you just throw away the data without writing it to disk. Job done.īy doing it this way 'testing' the archive becomes a free operation. If you do the check before writing you can effectively stream the archive through the decompressor, through your error checking algorithm, then out to disk and assume that the disk subsystem knows what it's doing. I'm assuming in this case that disk reading and writing are the slowest part of the process. With a large archive or on a memory constrained system this could double the time taken to decompress a file which would be unacceptable. Otherwise you are wasting precious resources reading from the archive, writing it to disk, then re-reading the on-disk data to do error checking. In decompressing a file it makes a lot of sense, from an efficiency perspective, to do the error checking before writing data to disk. In order to verify that the data in an archive is correct when extracting it every file or block of data will have a CRC or error detection code associated with it.