cellular automata pbm generator

cap.c

/* 
 * Print Cellular Automata output in netpbm format.
 * 
 * All rights reversed.
 * 2012 Remo Giermann <mo@liberejo.d>
 *
 */
#include <stdio.h>
#include <stdlib.h>

#define W 1000

void usage(const char *p)
{
        printf("Usage: %s [-h|--help] [black|white] [rRULE] [wWIDTH] [OUTFILE]\n", p);
        exit(0);
}

void pbm(int *u, size_t w, size_t h, FILE *o, int b, const char *desc)
{
        int x, y;
        fprintf(o, "P1\n# %s\n%u %u\n", desc, w, h);
        for (y=0; y<h; y++) {
                for (x=0; x<w; x++)
                        fprintf(o, "%u ", u[y*w+x]?b:!b);
                putc(10, o);
        }
}

int ca(int *u, size_t w, size_t max, int rule)
{
        int x, t;
        for (t=0; t<max-1; t++) {
                for (x=0; x<w; x++) {
                        int l = x==0? 0: u[t*w+x-1];
                        int c = u[t*w+x];
                        int r = x==w-1? 0: u[t*w+x+1];
                        int n = (l<<2)|(c<<1)|(r<<0);
                        u[(t+1)*w+x] = (rule&(1<<n))>>n;
                }
                if (u[t*w] && u[t*w+w-1]) break;
                fprintf(stderr, "\r%u", t);
        }; putc(10, stderr);
        return t+1;
}

int main(int argc, const char **argv)
{
        int t, *u, b=1, w=W, r=30, h=0;
        FILE *out = stdout;
        char c[32];
        while (--argc > 0) {
                if (strcmp(argv[argc], "-h") == 0 || strcmp(argv[argc], "--help") == 0) 
                        usage(argv[0]);
                else if (strcmp(argv[argc], "black") == 0) b = 0;
                else if (strcmp(argv[argc], "white") == 0) b = 1;
                else if (sscanf(argv[argc], "%c%u", c, &t) == 2 && *c == 'r' || *c == 'w') {
                        if (*c == 'r') r = t;
                        else if (*c == 'w') w = t;
                }
                else if (!(out = fopen(argv[argc], "w"))) {
                        perror(argv[argc]); usage(argv[0]);
                }
        }

        h = w*3/2;
        u = malloc(w*h*sizeof(int));
        u[w/2] = 1;

        sprintf(c, "CA rule %u", r);
        t = ca(u, w, h, r);
        pbm(u, w, t, out, b, c);

        return 0;
}