NES Header Checker

header-check.c

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

#include "ines-header.h"

#define max(a,b) \
	({ __typeof__ (a) _a = (a); \
		__typeof__ (b) _b = (b); \
		_a > _b ? _a : _b; })

static const char magic[4] = { 0x4E, 0x45, 0x53, 0x1A };

const char * toBool(unsigned char val) {
	return val ? "Yes" : "No";
}

const char * getArrangement(unsigned char low, unsigned char high) {
	char val = (high << 1) | low;

	switch (val) {
	case 0: return "Vertical Arrangement / Horizontal Mirroring";
	case 1: return "Horizontal Arrangement / Vertical Mirroring";
	case 2: return "2x2 (4 Page) Grid (No Mirroring)";
	default: return "UNKNOWN (Bad Value)";
	}
}

const char getMapper(unsigned char low, unsigned char high) {
	return (high << 4) | low;
}

const char * getTVSystem(unsigned char system) {
	return system ? "PAL" : "NTSC";
}

int main(int argc, const char **argv) {
	if (argc != 2) {
		fprintf(stderr, "usage: %s <.NES rom or header binary>\n", argv[0]);
		return 1;
	}

	FILE *file = fopen(argv[1], "rb");
	if (!file) {
		fprintf(stderr, "could not open file");
		return 1;
	}

	INESHeader header;

	size_t count = fread(&header, 1, sizeof(header), file);
	if (count != sizeof(header)) {
		fclose(file);
		fprintf(stderr, "could not read file; is it 16 bytes long?\n");
		return 2;
	}

	fclose(file);

	if (memcmp(&header.magic, &magic, 4) != 0) {
		fprintf(stderr, "given file has an invalid magic number\n");
		return 3;
	}

	printf(
		"Mapper:\t\t%03d\n"
		"TV System:\t%s\n"
		"PRG ROM size:\t%dKb (%d 16Kb banks)\n"
		"PRG RAM size:\t%dKb (%d 8Kb banks)\n"
		"CHR ROM size:\t%dKb (%d 8Kb banks)\n"
		"Arrangement:\t%s\n"
		"Trainer?:\t%s\n"
		"Battery RAM?\t%s\n"
		"iNES2 Header?\t%s\n"
		"Playchoice-10?\t%s\n"
		"VSUnisystem?\t%s\n",

		getMapper(header.mapperLow, header.mapperHigh),
		getTVSystem(header.tvSystem),
		header.prgRomSize * 16, header.prgRomSize,
		max(1, header.prgRamSize) * 8, max(1, header.prgRamSize),
		header.chrRomSize * 8, header.chrRomSize,
		getArrangement(header.arrangementLow, header.arrangementHigh),
		toBool(header.hasTrainer),
		toBool(header.hasBatteryRam),
		toBool(header.ines2Header),
		toBool(header.playchoice10),
		toBool(header.vsUnisystem));

	return 0;
}

index-header.h

typedef struct __attribute__((packed)) {
	unsigned char magic[4];
	unsigned char prgRomSize;
	unsigned char chrRomSize;

	unsigned char arrangementLow : 1;
	unsigned char hasBatteryRam : 1;
	unsigned char hasTrainer : 1;
	unsigned char arrangementHigh : 1;
	unsigned char mapperLow : 4;

	unsigned char vsUnisystem : 1;
	unsigned char playchoice10 : 1;
	unsigned char ines2Header : 2;
	unsigned char mapperHigh : 4;

	unsigned char prgRamSize;

	unsigned char tvSystem : 1;
	unsigned char reserved : 7;

	unsigned char reservedZeroFill[6];
} INESHeader;