refactor iNES parser

1 files changed, 9 insertions, 18 deletions

diff --git a/lib/nes/cartridge.cc b/lib/nes/cartridge.cc
index 6a60741..bd8e7d3 100644
--- a/lib/nes/cartridge.cc
+++ b/lib/nes/cartridge.cc
@@ -17,41 +17,32 @@ namespace nes
 		auto res = cartridge{ status::success };
 
 		// Parse header.
-		if (length < 16) { return cartridge{ status::error_invalid_ines_data }; }
-		if (bytes[0] != 'N' || bytes[1] != 'E' || bytes[2] != 'S' || bytes[3] != 0x1A)
+		if (length < header_length) { return cartridge{ status::error_invalid_ines_data }; }
+		auto const h = header{ bytes };
+		if (h.get_magic_0() != 'N' || h.get_magic_1() != 'E' || h.get_magic_2() != 'S' || h.get_magic_3() != 0x1A)
 		{
 			return cartridge{ status::error_invalid_ines_data };
 		}
-		auto const prg_rom_banks = bytes[4];
-		auto const chr_rom_banks = bytes[5];
-		auto const control_1 = bytes[6];
-		auto const control_2 = bytes[7];
-		auto const ram_banks = (bytes[8] != 0) ? bytes[8] : 1u;
-		auto const has_trainer = (control_1 & 0b00000100) != 0;
-		auto const mapper_number = static_cast<std::uint8_t>(
-			(control_1 & 0b11110000) >> 4 |
-			(control_2 & 0b11110000) >> 0);
+		auto const mapper_number = static_cast<std::uint8_t>((h.get_mapper_high() << 4) | (h.get_mapper_low() << 0));
 
 		res.mapper_ = &mapper::get(mapper_number);
-		res.name_table_arrangement_ = (control_1 & 0b00000001) != 0
-			? name_table_arrangement::vertical
-			: name_table_arrangement::horizontal;
+		res.name_table_arrangement_ = h.get_name_table_arrangement();
 
 		// Load program data.
 		auto offset = std::size_t{ 16 };
-		if (has_trainer) { offset += 512; }
+		if (h.get_has_trainer()) { offset += 512; }
 
-		auto const prg_rom_size = prg_rom_banks * prg_rom_bank_size;
+		auto const prg_rom_size = h.get_prg_rom_banks() * prg_rom_bank_size;
 		if (length < offset + prg_rom_size) { return cartridge{ status::error_invalid_ines_data }; }
 		res.prg_rom_ = std::vector(&bytes[offset], &bytes[offset + prg_rom_size]);
 
 		offset += prg_rom_size;
 
-		auto const chr_rom_size = chr_rom_banks * chr_rom_bank_size;
+		auto const chr_rom_size = h.get_chr_rom_banks() * chr_rom_bank_size;
 		if (length < offset + chr_rom_size) { return cartridge{ status::error_invalid_ines_data }; }
 		res.chr_rom_ = std::vector(&bytes[offset], &bytes[offset + chr_rom_size]);
 
-		res.ram_ = std::vector(ram_banks * ram_bank_size, std::uint8_t{ 0 });
+		res.ram_ = std::vector(std::max(h.get_ram_banks(), 1u) * ram_bank_size, std::uint8_t{ 0 });
 
 		if (auto const status = res.get_mapper().validate(res); status != status::success)
 		{