// Generate random images from a DAG quadtree.
// Except this is doing the iteration inside-out, with a very interesting effect
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
enum { n_levels = 9, n_nodes = 8 };
static unsigned char tree[n_levels][n_nodes][4];
/* static unsigned char palette[256][3]; */
static void
randomize()
{
fread(tree, sizeof(tree), 1, stdin);
/* for (size_t ii = 0; ii < sizeof(tree); ii++) */
/* ((char*)tree)[ii] = random(); */
/* for (size_t ii = 0; ii < sizeof(palette); ii++) */
/* ((char*)palette)[ii] = random(); */
}
static int
pixel(int zorder)
{
int nn = 0;
for (int ii = 0; ii < n_levels; ii++)
nn = tree[ii][nn & (n_nodes - 1)][zorder >> 2 * ii & 3];
return nn;
}
// Copied and pasted from Hacker's Delight:
// Perfect outer shuffle coded as swaps [GLS] (30 Brisc instructions).
unsigned shuffle2(unsigned x) {
unsigned t;
t = (x ^ (x >> 8)) & 0x0000FF00; x = x ^ t ^ (t << 8);
t = (x ^ (x >> 4)) & 0x00F000F0; x = x ^ t ^ (t << 4);
t = (x ^ (x >> 2)) & 0x0C0C0C0C; x = x ^ t ^ (t << 2);
t = (x ^ (x >> 1)) & 0x22222222; x = x ^ t ^ (t << 1);
return x;
}
static void
generate_ppm()
{
printf("P6\n%d %d\n255\n", 1 << n_levels, 1 << n_levels);
for (int yy = 0; yy < 1 << n_levels; yy++)
for (int xx = 0; xx < 1 << n_levels; xx++) {
int pix = pixel(shuffle2(yy << 16 | xx));
putchar(pix); putchar(pix); putchar(pix);
/* fwrite(&palette[pix], 3, 1, stdout); */
}
}
int
main(int argc, char **argv)
{
srandom((argc == 1) ? getpid() : atoi(argv[1]));
randomize();
generate_ppm();
return 0;
}
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