16-bit ROM merger

merger.c

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <stddef.h>

int main(int argc, char *argv[])
{
	const size_t	bufsize = 4096;
	uint8_t			buf_a[bufsize];
	uint8_t			buf_b[bufsize];
	uint8_t			buf_c[bufsize * 2];

	if (argc != 4) {
		fprintf(stderr, "usage: merged <msb_file> <lsb_file> <out_file>\n");
		return EXIT_FAILURE;
	}

	int	a = open(argv[1], O_RDONLY);
	if (a < 0) {
		fprintf(stderr, "couldn't open MSB file\n");
		return EXIT_FAILURE;
	}
	int b = open(argv[2], O_RDONLY);
	if (b < 0) {
		fprintf(stderr, "couldn't open LSB file\n");
		return EXIT_FAILURE;
	}
	int c = open(argv[3], O_RDWR | O_CREAT, 0644);
	if (c < 0) {
		fprintf(stderr, "couldn't open output file\n");
		return EXIT_FAILURE;
	}

	while (1) {
		ssize_t n_a, n_b;
		if ((n_a = read(a, &buf_a, bufsize)) <= 0) break;
		if ((n_b = read(b, &buf_b, bufsize)) != n_a) break;

		uint8_t *p = buf_c;
		for (int i = 0; i < n_a; ++i) {
			*p++ = buf_a[i];
			*p++ = buf_b[i];
		}
		write(c, &buf_c, bufsize * 2);
	}

	close(a);
	close(b);
	close(c);
}

This program can re-combine the separate 8-bit ROMs found in some old 16-bit gear into a single file for subsequent analysis.