We overwrite a few preceding bytes to add lsl r0, r0, #1 (logical shift left by 1 = multiply by 2), then return.
Original bytes: 00 00 47 70 Patch to: 40 00 47 70 pokemon fire red exp multiplier x2
00 00 47 70 to:
1. Objective To modify the game code of Pokémon Fire Red (USA, Rev 1) so that any experience points (EXP) earned after a battle are automatically doubled before being added to a Pokémon’s total EXP. We overwrite a few preceding bytes to add
0x08023C20: 4770 bx lr (returns)
00 00 00 00 40 00 47 70 Wait — this misaligns. The correct minimal patch (tested working) is: pokemon fire red exp multiplier x2