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Kaphotics

LGPE Code Reverse Engineering

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Starting a topic related to reverse engineering game code, specific for the switch pkm titles.

Reverse engineering code of Nintendo Switch titles is most commonly done with the Interactive Disassembler (IDA) and the Hex-Rays extension, which converts the assembly code to easier to understand c code. Using SwitchIDAProLoader, you can load the game .nso file which generates the .i64 database used for 'disassembling' the game code.

With the disassembly in hand and a blind understanding of how the code is laid out, finding your bearings within the millions of instructions is hard. It is recommended to search for a sequence of values, such as the list of TM Moves (ordered TM01, TM02, TM03), then branch out from there. Keep in mind that the games were programmed by humans, but the compiler may optimize things into relative gibberish.

Useful hotkeys:

F5 with cursor placed on/within a function = go to function definition
x = cross reference list for selected variable/function
/ = add new comment
n = rename variable/function
escape = go back (e.g. if you go to definition then press escape, this will pop you back out to where you were before peeking).

Here's some hints:

  • byte sequence (68 96 40 39 94 06 00 11 9F 02 08 6B). This will put you in the method that creates the pkm's PID, which is called every time a new Pokémon is generated (sub_71007399B0).
  • Search "Immediate value" for '632' (Shiny Charm item ID). Filter by MOV instruction. The third result=sub_71002F6760 (which is the first that actually uses 632 immediately in a function call) is the wild catch combo shiny rate/IV determination method.
  • Search "Immediate value" for '874' (new Silph Scope item ID). Filter results by MOV instruction again. This will get you the 'has inventory item' function (first=sub_71002BF180 and second result=sub_71002fe3c8).
  • The latter result from above is the main wild spawn function :)
  • sub_7100300B84 (gets the Height group xs/s/normal/l/xl) which is called by the above method, is also used by sub_710082D89C. This method is the 'exp boost' factor which gives bonuses based on throw type/etc.

Feel free to discuss your findings about the game code here!

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