Hi folks. Since I started at GD, I’ve been away from the blog, but here’s a format I’ve been working on for a while: IPS, or International Patching Specification.
My last entry about ROM hacking only discussed what a person does to make a hack. But with a mind for distribution, no hack would ever legally pass muster without some sort of patching scheme. This involves a format that facilitates patching, and software applications that can make and apply such patches.
A patch file contains only changes to a file. Suppose you have version A and version B of a file: the patch, once applied to A, will “transform” A into B, provided you have version A to begin with.
The most common type of patch file used in ROM hacks is IPS, and for good reason:
1) It’s common.
2) It’s simple.
3) It works well with small binaries.
A number of utilities exist to apply patches, such as IPSWin.exe. It applies patch files with IPS extensions to whole ROMs or other files. Generally speaking, you cannot distribute the whole ROMs legally to another person, but you can distribute the patch, which contains only changes you’ve made personally.
There is a lot of legal gray area here. But I’m not concerned with that–and neither should you. What concerned me was that I never found many utilities that could make IPS files in the way I wanted.
I went to work on BARfly and made a new I.F. called IPS.BAR. This file actually has three functions rolled into one:
1) It characterizes patch records of an existing IPS file.
2) It allows you to patch a file using version A of a file and an IPS file.
3) It allows you to make an IPS from version A and version B of a file.
It’s #3 that is most useful to me. I had to give it some thought, because there are some nuances to making a patch have a small size. Run-length encoding is supported in IPS, so I took advantage of that whenever possible.
When testing it out, I was shocked to discover that in some cases, IPS.BAR generated patch files nearly half the size of some of the originals I’ve found online!
Anyway, I’m satisfied with the utility, and I encourage anyone who wants to learn about IPS to check out the new file on my website. Download it here: http://www.chriskallen.com/barfly/IPS_Patch_File.bar.
I will note that the instructions are not that straightforward because they involve some copying, pasting, and deleting. This is because BARfly’s original charter was to characterize data formats. Its utility in performing more complex file operations is limited as a result. I will be changing this soon, of course. Having a schema have diverse file inputs and file outputs raises the “BAR” significantly–pun intended.