How To Find Offets Of Data In Compressed ROMs

[Deleted]

Today I am going to teach you how to find data in a compressed ROM, in other words, any ROM other than the Debug ROM.

Requirements:
Any Zelda ROM other than the Debug ROM.
A Hex Editor
UoT*
Zelda Resource Extractor* (Comes with UoT)
Pen and Paper/Notepad

*Only needed if you're finding something other than a Map/Scene.

I will be using Majora's Mask (U) as an example.

Step 1 - Finding a file you want to find in the ROM.

Maps/Scenes:
First, go here:
www.64.vg/wiki/index.php?title=Zelda_64_Scene_Listings
And write down the offsets of the Map/Scene you want to find.*
These are its uncompressed offsets.
*if you are using OoT v1.0 (U), write down the compressed offsets, and go straight to step 3.

Other Data
Extract the ROM you are using, with ZRE.
Open the files in UoT until you find one you want to find in the ROM.
Write down the name of the file, this is its uncompressed offset in the ROM.

Step 2 - Finding the compressed offset in the ROM.

Go to
Search > Find...
And type in the uncompressed offset of your data.

Do not try to go to the uncompressed offset, as in most cases it doesn't even exist, and it will not be what you are looking for if it does.

You should get results from your search that look like:

xx xx xx xx : yy yy yy yy | aa aa aa aa : bb bb bb bb

Where
xx xx xx xx : yy yy yy yy
Is the uncompressed start and end offsets of the data.

And
aa aa aa aa : bb bb bb bb
Is the compressed start and end offsets of the data.

Now write down what aa aa aa aa is, and bb bb bb bb, for reference.

Example:



You can see in the picture, I searched for 02E5C000, which is the uncompressed starting offset of South Clock Town.

My results:

xx xx xx xx

yy yy yy yy

[/color][/td][td]aa aa aa aa[/td][td]bb bb bb bb[/color][/td][/tr][tr][td]02 E5 C0 00[/td][td]02 E6 F8 B0[/td][td]01 E6 1E 30[/td][td]01 E6 8E 10[/td][/tr][/table]

Step 3 - Finding the Data.

Simple. Just go
Address > Go To...
And type in the value you wrote down for aa aa aa aa.

Example:



And there you have it, you have found your compressed data!

I hope you found this useful. ;D
It was a bit of a pain to write, because I accidentally deleted it all and had to start again.
I figured this out and wrote it all by myself.

Here are some useful Map offsets (compressed) for Majora's Mask (U):
01E61E30 - South Clock Town
01E46670 - North Clock Town
01E367F0 - East Clock Town
01E1D740 - West Clock Town

[snotskie]

oooohhhhhhhhh
now i get it
this is what i was always having trouble with when i tried to mod, it wouldnt write to the right offset, if it was righting at all

[spinout]

Protip - Don't try to hack Yaz0 blocks.
Use a Yaz0 decoder to decompress the map, and use a Yaz0 encoder to re-compress it. Or, use ZDec to decompress your ROM file.

[Deleted]

True, but it helps to know where they are if you're extracting them manually, and so you can insert them back in at the same point if you've edited them and re-comressed them.

[spinout]

...I thought that was assumed with my post, because if you are to decompress a resource file (map, scene, object, actor etc) you have to know it's [physical] offset

[Deleted]

Lol I think I misunderstood.
You couldn't try to hack it anyway if you don't first know where it is.
My post doesn't make much sense after yours now I re-read them.

Lol I have hacked a Yaz0 block before, sometimes it seems ok and works but sometimes it can do crazy things to the map, like for some reason all the textures disappeared one time.
I only just found a Yaz0 encoder though, and I'm still yet to test it out.

[Axel]

Thank You! I tried doing this once. I ended up Corrupting my Rom. I had to get a New one from Ash.