generate crc value for file(s) ?

elektron · 07-09-2004, 04:05 AM

Quote:

Originally posted by Dark_Helmet

elektron:
Take that code and run with it

Just a pointer: I noticed you swapped some things around a bit; All those "return X" statements for unexpected error conditions were to give a non-zero exit result for the program (just to follow traditional *nix guidelines). In your computeCRC32 function, you return 0 on those same error conditions. The only problem I see is that value gets assigned to the crc value. In theory, 0x00000000 is a valid CRC 32 value. It might be rare (specifically a 1 in about 4 billion chance), but in such a case, you wouldn't be able to distinguish whether it's a legitimate CRC or an error.

sure. the functions return an unsigned long value, which doesn't necesarily support returning negative numbers and as you point out zero and positive numbers are possible crc values. i don't code c to often. in python i could just raise an exception on an error. but i digress, this will of course need to be addressed.

Quote:

Also, you have a slight memory leak... Here's the sequence:
1. The malloc() in generateCRC32() goes off without a hitch
2. Suppose the open() call fails (returns -1)
In that scenario, you return from the generateCRC32() without freeing the memory for file_buffer. If the user supplied more than one filename on the command line, the possibility exists that you could chew through memory quickly.

this is a good point, there is a possibility of that, and it can be remedied easily. coming from more of a scripting background, it's easy to forget to check for such things in a c program. thank you ^_^

elektron · 07-09-2004, 07:10 AM

both of the aforementioned bugs should be fixed and avail at : http://kremlor.net/projects/crc32/

Apostasy · 07-09-2004, 01:15 PM

corruption is not really viable.. seeing how calcchecksum app is giving me the values that correspond to the filenames.. so that is what i'm currently using for files which i do not know the values of.
as for the 'container' format i mentioned.. an .ogm or .mkv video file usually has a video track.. multiple audio tracks (languages) and subtitle text files all in one file.. it is even possible to have multiple video tracks in the same file... although i have not yet seen that yet in any of my files. a compatible media player can switch subs or audio tracks at the users command.. much like watching a dvd in your livingroom. if an avi is also a container format forgive me,, i didn't know that.

bbiaf.. must try that new code

<EDIT>
[root@boojie Puni Puni Poemy]# crc32 Puni.Puni.Poemy.01.Poemi.Is.In.A.Bad.Mood.\[AXP.DVDRip\].\[Dual.Audio\].\[7A9F8C2A\].ogm
Puni.Puni.Poemy.01.Poemi.Is.In.A.Bad.Mood.[AXP.DVDRip].[Dual.Audio].[7A9F8C2A].ogm 0x7A9F8C2A

success! </EDIT>