CHD CDs are not reproducible between 2048B/2352B sector images that convey the same information

[chungy]

MAME version

0.269

System information

n/a

INI configuration details

n/a

Emulated system/software

n/a

Incorrect behaviour

In CD-ROM images, sync, address, EDC, and ECC subchannels are normally constructed from well-known methods and MODE1 discs that do not perform any tricks should be reconstructable to the original physical format image from a 2048B sector ("cooked") image. This is the case for the vast majority of MODE1 discs without physical DRM applied to them.

The bin2ecm utility is an example program that takes advantage of this fact to offer high compressability to 2352B sector ("raw") images: https://github.com/chungy/cmdpack/blob/master/bin2ecm.txt

Expected behaviour

I believe that since CHDs are supposed to represent CD-ROMs, the input of 2048B sector images should end up with the same CHD as a 2352B sector image conveying the same data without any subchannel manipulation.

Steps to reproduce

Here is an image for demonstration purposes:

test.zip

If you create a CHD in the two ways, chdman createcd -i test.toc ... and chdman createcd -i test.iso ..., you get distinct CHDs with different SHA1s. If you mount or burn test.iso and use cdrdao read-cd --device /dev/srN --read-raw --datafile new.dat new.toc, you will notice the new.dat will match with identical data as in the test archive. The subchannel data is not manipulated and can be reproduced exactly, hence proving its identity with the "cooked" image.

Additional details

No response