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

#define	BUFSIZE		(4096 * 1024)
#define	BUFSIZE_HALF	(BUFSIZE / 2)

static unsigned char	in_buffer[BUFSIZE];
static unsigned char	out_buffer[BUFSIZE_HALF];

int	main(int argc, char *argv[])
{
	FILE	*fp;
	int	i;

	if (argc < 3) {
		printf("%s [infile] [outfile]\n", argv[0]);
		goto fin0;
	}

	fp = fopen(argv[1], "r");
	if (fp == NULL) {
		printf("file open error (%s)\n", argv[1]);
		goto fin0;
	}
	memset(in_buffer, ~0, sizeof(in_buffer));
	fread(in_buffer, 1, sizeof(in_buffer), fp);
	fclose(fp);

	for (i = 0; i < sizeof(out_buffer); i += 2) {
		out_buffer[i + 0] = in_buffer[i];
		out_buffer[i + 1] = in_buffer[i + BUFSIZE_HALF];
	}

	fp = fopen(argv[2], "w");
	if (fp == NULL) {
		printf("file open error (%s)\n", argv[2]);
		goto fin0;
	}
	fwrite(out_buffer, sizeof(out_buffer), 1, fp);
	fclose(fp);

fin0:
	return 0;
}