emu_nes/rom.c

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

#include "rom.h"

void
parse_rom(const uint8_t *data, size_t data_len, struct rom *rom)
{
	size_t prg_rom_offset = 16;
	size_t chr_rom_offset = 0;

	if (data_len < 16) {
		fprintf(stderr, "Invalid ROM: size less than 16 bytes\n");
		exit(1);
	}

	if (data[0] != 'N' || data[1] != 'E' || data[2] != 'S' || data[3] != 0x1A) {
		fprintf(stderr, "Invalid ROM: not in iNES format\n");
		exit(1);
	}

	/* trainer data present */
	if (data[6] & (1 << 2))
		prg_rom_offset += 512;

	rom->prg_rom_size = data[4] * 0x4000;
	rom->prg_rom = calloc(rom->prg_rom_size, 1);
	memcpy(rom->prg_rom, data + prg_rom_offset, rom->prg_rom_size);

	rom->chr_rom_size = data[5] * 0x2000;
	if (rom->chr_rom_size > 0) {
		rom->chr_rom = calloc(rom->chr_rom_size, 1);
		chr_rom_offset = prg_rom_offset + rom->prg_rom_size;
		memcpy(rom->chr_rom, data + chr_rom_offset, rom->chr_rom_size);
	}

	if ((data[6] & (1 << 3)) != 0)
		rom->mirror = M_FOUR;
	else if ((data[6] & 1) == 1)
		rom->mirror = M_VERTICAL;
	else if ((data[6] & 1) == 0)
		rom->mirror = M_HORIZONTAL;

	rom->mapper = (data[6] & (0xF << 4)) >> 4;
	rom->mapper |= data[7] & (0xF << 4);
}

void
free_rom(struct rom *rom)
{
	free(rom->prg_rom);
	if (rom->chr_rom_size > 0)
		free(rom->chr_rom);
}