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fix rom checksum #272

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Merged
blkerby merged 5 commits into from
Jan 17, 2026
Merged

fix rom checksum #272

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d9e4d6d
fix rom checksum
nn357 Jan 16, 2026
90fe291
update formatting
nn357 Jan 16, 2026
aac4bb0
formatting?
nn357 Jan 16, 2026
4485db4
Update rust/maprando/src/patch.rs
blkerby Jan 17, 2026
4685d9d
Update rust/maprando/src/patch.rs
blkerby Jan 17, 2026
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24 changes: 24 additions & 0 deletions rust/maprando/src/patch.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -3306,6 +3306,27 @@ fn get_other_door_ptr_pair_map(map: &Map) -> HashMap<DoorPtrPair, DoorPtrPair> {
other_door_ptr_pair_map
}

fn fix_snes_checksum(rom: &mut Rom) {
const CHECKSUM_ADDR: usize = 0x7FDC; // LoROM

let data = &mut rom.data;
let mut sum: u32 = 0;

data[CHECKSUM_ADDR..CHECKSUM_ADDR + 2].fill(0xFF); // clear out the checksum
data[CHECKSUM_ADDR + 2..CHECKSUM_ADDR + 4].fill(0x00); // and the compliment

for &b in data.iter() {
sum = sum.wrapping_add(b as u32);
}

let checksum = (sum & 0xFFFF) as u16;
let complement = checksum ^ 0xFFFF;

data[CHECKSUM_ADDR..CHECKSUM_ADDR + 2].copy_from_slice(&complement.to_le_bytes());

data[CHECKSUM_ADDR + 2..CHECKSUM_ADDR + 4].copy_from_slice(&checksum.to_le_bytes());
}

pub fn make_rom(
base_rom: &Rom,
randomizer_settings: &RandomizerSettings,
Expand Down Expand Up @@ -3408,5 +3429,8 @@ pub fn make_rom(
mosaic_themes,
)?;

// ROM Checksum: Do not modify the ROM contents after this point
fix_snes_checksum(patcher.rom);

Ok(rom)
}