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 Post subject: ColecoVision romlib CRC32 Format
PostPosted: Wed Apr 23, 2008 10:32 am 

Joined: Wed Apr 23, 2008 10:10 am
Posts: 6
I have a number of roms that I would like to add to the romlib.ini file but am struggling to understand how the current decimal CRC32's have been calculated, for example:

1. The existing romlib.ini has 2010 - The Graphic Action Game listed with a CRC32 of -982144975. Using a CRC32 program I have determined that the CRC32 of my 2010 rom file is c575a831 (my rom is definately the same as the one expected because the MD5's match up). Now if I use the Window's calculator or Excel to convert from HEX to DEC then this gives a decimal CRC32 of 3312822321. Not a match!

2. Another example, where the romlib.ini has a positve decimal CRC, works for me. For Alphabet Zoo the romlib CRC32 = 1341869708. The CRC32 for my rom file is 4ffb4e8c which converts in Excel to 1341869708. A match.

So how should I convert my hex CRC32's to decimal CRC32's to match how the studio software uses them? How important is the CRC32 to the studio software? Why does it not just use the MD5 which is a much more reliable measure?

Out of interest what does the FORMAT = 0 line do? What happens if I change the format to 1, 2 etc. ?

Many thanks for any help.


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 Post subject: Re: ColecoVision romlib CRC32 Format
PostPosted: Thu Apr 24, 2008 10:56 am 
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Joined: Tue Aug 05, 2003 9:55 am
Posts: 1035
Location: Cleveland, Ohio
ikrananka wrote:
2. Another example, where the romlib.ini has a positve decimal CRC, works for me. For Alphabet Zoo the romlib CRC32 = 1341869708. The CRC32 for my rom file is 4ffb4e8c which converts in Excel to 1341869708. A match.


The CRC32s are calculated as unsigned 32-bit values but the ini file library for some reason stores them as signed integers. I am not sure of the exact method used in conversion, but it should be the same one used by the windows registry to store signed integers.

You can add rom images to the library from the studio software as well, just load the rom into a workbook, assign it a name and then right-click and use the add to library option.

Quote:
How important is the CRC32 to the studio software? Why does it not just use the MD5 which is a much more reliable measure?


I believe I added MD5 after CRC32 because there was less chance of a collision, but left CRC32 in place anyway so the old ini files from the first version would still be compatible.

Quote:
Out of interest what does the FORMAT = 0 line do? What happens if I change the format to 1, 2 etc. ?


For Colecovision roms the format is always zero, it is only used otherwise in the 5200 romlib.ini.

Steve


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 Post subject: Re: ColecoVision romlib CRC32 Format
PostPosted: Thu Apr 24, 2008 12:00 pm 

Joined: Wed Apr 23, 2008 10:10 am
Posts: 6
classics wrote:
The CRC32s are calculated as unsigned 32-bit values but the ini file library for some reason stores them as signed integers. I am not sure of the exact method used in conversion, but it should be the same one used by the windows registry to store signed integers.

You can add rom images to the library from the studio software as well, just load the rom into a workbook, assign it a name and then right-click and use the add to library option.


Looks like the standard Excel functions and the Windows calculator can't do signed integer conversions. Using a signed 32-bit integer conversion works - thanks for pointing me in the right direction. I'll probably just add the new roms through the studio software - much easier anyway :D

Thanks for the info on the other parts of the ini file structure - I'm a curious guy.


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