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

#define	PIXEL	4

struct yjk {
	int16_t	y;
	int16_t	j;
	int16_t	k;
} __attribute__((packed));

static	void	avgjk(struct yjk *yjk, int pixels)
{
	int	i, j, k;

	j = 0;
	k = 0;
	for (i = 0; i < pixels; i++) {
		j += (int16_t)le16toh(yjk[i].j);
		k += (int16_t)le16toh(yjk[i].k);
	}

	j /= pixels;
	k /= pixels;

	for (i = 0; i < pixels; i++) {
		yjk[i].j = le16toh((int16_t)j);
		yjk[i].k = le16toh((int16_t)k);
	}
}

static	void	clampyjk(struct yjk *yjk, int pixels)
{
	int	i;

	for (i = 0; i < pixels; i++) {
		yjk[i].y &= ~0x3f;
		yjk[i].j &= ~0x1f;
		yjk[i].k &= ~0x1f;
	}
}

static	void	filter(FILE *fpi, FILE *fpo)
{
	struct	yjk	yjk[PIXEL];

	while (1) {
		if (fread(yjk, 1, sizeof(yjk), fpi) < sizeof(yjk)) break;

		avgjk(yjk, PIXEL);
		clampyjk(yjk, PIXEL);

		if (fwrite(yjk, sizeof(yjk), 1, fpo) < 1) {
			fprintf(stderr, "filter: file write error\n");
			break;
		}
	}
}

int	main(int argc, char *argv[])
{
	FILE	*fpi, *fpo;

	if (argc < 2) {
		fprintf(stderr, "usage: %s [(infile)] [(outfile)]\n", argv[0]);
		goto fin0;
	}

	if (argc < 2 || !strcmp(argv[1], "-")) {
		fpi = stdin;
	} else {
		fpi = fopen(argv[1], "r");
		if (fpi == NULL) {
			fprintf(stderr, "file open error (in)\n");
			goto fin0;
		}
	}

	if (argc < 3 || !strcmp(argv[2], "-")) {
		fpo = stdout;
	} else {
		fpo = fopen(argv[2], "w");
		if (fpo == NULL) {
			fprintf(stderr, "file open error (out)\n");
			goto fin1;
		}
	}

	filter(fpi, fpo);

//fin2:
	if (fpo != stdout) fclose(fpo);
fin1:
	if (fpi != stdin) fclose(fpi);
fin0:
	return 0;
}