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

#define W 4096
#define H 4096

uint32_t p[H][W];

#define RGBA_LE(R, G, B, A) ((R)|((G)<<8)|((B)<<16)|((A)<<24))
#define RGBA_BE(R, G, B, A) (((R)<<24)|((G)<<16)|((B)<<8)|(A))
#define RGBA RGBA_LE
#define RGB(R, G, B) RGBA(R, G, B, 255)

int err_stdout(void) {
	if (ferror(stdout))
		perror(NULL);
	else
		fprintf(stderr, "unexpected error on stdout\n");
	return 1;
}

// not ideal random number generator
#define RANDOM(N) (random()%(N))

void shuf_uint32_t(uint32_t *p, size_t n) {
	uint32_t *i = p;
	uint32_t tmp;
	if (n < 2)
		return;
	while (n) {
		size_t r = RANDOM(n);
		tmp = i[r];
		i[r] = i[0];
		i[0] = tmp;
		++i, --n;
	}
}

int main()
{
	int rv;
	rv = printf(
		"P7\n"
		"WIDTH %d\n"
		"HEIGHT %d\n"
		"DEPTH 4\n"
		"MAXVAL 255\n"
		"TUPLTYPE RGB_ALPHA\n"
		"ENDHDR\n",
		W, H
	);
	if (rv < 0)
		return err_stdout();
	uint32_t i = 255<<24;
	for (int y=0; y<H; ++y) {
		for (int x=0; x<W; ++x) {
			p[y][x] = i++;
		}
	}
	shuf_uint32_t(&p[0][0], W*H);
	rv = fwrite(p, sizeof(p), 1, stdout);
	if (rv != 1)
		return err_stdout();
	return 0;
}