calculate the crc32 of a wxString

SuperPat · Post by **SuperPat** » Sun Mar 05, 2006 12:25 pm

Hello,

How to calculate the crc32 string of a wxString?

Post by **Jorg** » Sun Mar 05, 2006 1:03 pm

Not that hard. You can start with a 32 bits begin hash (you will have to find a hastable) and then do the following:

- Fetch byte
- Shift byte into 32 bits from the left
- XOR with previous hash
- Set new hash as previous one

And continue to do this until you have shifted all bytes in there. You end up with a CRC32 hash you can use to test if your data is changed or not.

There are better ways, I think for more certaintly changed contents arte spotted. you should use a MD5 checksum. This one is more powerful.

- Jorgen

priyank_bolia · Post by **priyank_bolia** » Mon Mar 06, 2006 6:20 am

Jorg wrote: - Shift byte (8 bits) into 32 bits from the left

Post by **Jorg** » Mon Mar 06, 2006 7:56 am

Hi,

Isn't that what I wrote? Anyway, if it was unclear thanks for clarifiying for me

It was written around 10:00 dutch time so I am pretty impressed with my own clarification at that hour

- Jorgen

priyank_bolia · Post by **priyank_bolia** » Mon Mar 06, 2006 8:46 am

For me it sounds like, that you want to shift 8 bits byte 32 bits left, that makes the value 0. May be I am wrong, but that what I make it out of the text.
NB: English is not the first language for me and many members here.

Post by **upCASE** » Mon Mar 06, 2006 8:55 am

Hi!
If you need a quick solution, wxChecksums (http://wxchecksums.sourceforge.net/mainpage_en.html) has support for CRC32, MD5 and SFV.

Post by **Jorg** » Mon Mar 06, 2006 8:59 am

Ahh ok. No that's not what I meant.

Good call upCASE

I still believe MD5 is better then CRC32. But it all depends on where you are going to use it for, or what the performance will be.

- Jorgen

Post by **upCASE** » Mon Mar 06, 2006 9:09 am

Jorg wrote:Good call upCASE I still believe MD5 is better then CRC32. But it all depends on where you are going to use it for, or what the performance will be.

Yes, it really depends as CRC and MD5 are more or less completely different. CRC, as the name suggest, is a cyclic redundancy algo, whereas MD5 is a hashing algo.
With CRC32 you can identify bit errors and (if I'm not mistaken) correct one bit erros. With MD5 this is not possible. But MD5 is more "secure".

priyank_bolia · Post by **priyank_bolia** » Mon Mar 06, 2006 9:11 am

Quick note that its under GPL license, one more dll