melonDS Pokémon gen 5 save state fixer

fix-pokemon-state.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdint.h>
#include <errno.h>

const char wifi[] = { 'W', 'I', 'F', 'I' };
const char mem_fill[] = { 0xA5, 0xA5, 0x5A, 0x5A };
uint8_t* state;

int main(int argc, char** argv) {
	if (argc > 2) {
		fprintf(stderr, "Usage: %s <state>\n", argv[0]);
		return 1;
	}
	
	FILE* f = fopen(argv[1], "rb");
	if (!f) {
		perror(argv[1]);
		return errno;
	}

	fseek(f, 0, SEEK_END);
	size_t size = ftell(f);
	fseek(f, 0, SEEK_SET);

	state = malloc(size);
	fread(state, size, 1, f);
	fclose(f);

	size_t offset = 0;

	int found = 0;
	while (!found) {
		for (size_t i = offset; i < size; i++) {
			if (memcmp(state + i, wifi, 4) == 0) {
				offset = i;
				break;
			}
		}

		if (offset == 0) {
			fprintf(stderr, "Couldn't find Wi-Fi data.\n");
			return 1;
		}

		size_t mem_offset = 0;
		for (size_t i = offset; i < offset + 32; i++) {
			if (memcmp(state + i, mem_fill, 4) == 0) {
				mem_offset = i;
			}
		}

		if (mem_offset == 0) {
			offset++;
			continue;
		}

		found = 1;
		offset = mem_offset;
	}

	size_t fix_offset = offset + 0x2208;

	if (state[fix_offset] != 1) {
		fprintf(stderr, "Doesn't look like a save state that needs to be fixed. (%08lx == %02x)\n", fix_offset, state[fix_offset]);
		return 1;
	}

	state[fix_offset] = 0x09;

	const char* fixed = ".fixed";
	char* new_name = malloc(strlen(argv[1]) + strlen(fixed));
	sprintf(new_name, "%s%s", argv[1], fixed);

	FILE* new_file = fopen(new_name, "wb");
	if (!new_file) {
		perror(new_name);
		return errno;
	}

	fwrite(state, size, 1, new_file);
	fclose(new_file);
}