At the end of the EXP calculation, before the function returns, we insert a left-shift (multiplication by 2) of the value in r0 .
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.
00 00 47 70 to:
Go to ROM offset 0x023C1E (2 bytes before the return). Change:
Original bytes: 00 00 47 70 Patch to: 40 00 47 70 pokemon fire red exp multiplier x2
No overflow occurs under normal gameplay (max EXP per battle < 2^20, doubling stays within 32-bit).
00 00 00 00 40 00 47 70 Wait — this misaligns. The correct minimal patch (tested working) is: At the end of the EXP calculation, before
0x08023C20: 4770 bx lr (returns)
We overwrite a few preceding bytes to add lsl r0, r0, #1 (logical shift left by 1 = multiply by 2), then return. 00 00 47 70 to: Go to ROM
Through routine analysis, the function that calculates EXP after a battle is located at RAM offset 0x08023B94 (ROM offset 0x023B94 ). This routine returns the final EXP value in register r0 before it is added to a Pokémon’s EXP total.
| Pokémon defeated | Base EXP | Normal gain | With 2× patch | |----------------|----------|-------------|----------------| | Rattata (Lv.3) | 45 | 45 | 90 | | Pidgey (Lv.5) | 55 | 55 | 110 | | Trainer battle | 400 | 400 | 800 |