Convert Sinclair ZX Spectrum images to Portable Bitmap format

zxtopbm.c

/* Convert Sinclair ZX Spectrum images to Portable Bitmap format
 * by William McBrine <wmcbrine@gmail.com>
 * October 16, 2005
 * Placed in the public domain
 *
 * This does only a monochrome conversion -- color is more complex. I'll 
 * call that one "zxtoppm", when I write it.
 */

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

#define SCREENSIZE 6144

int main(int argc, char **argv)
{
    FILE *inp;
    unsigned char rawbits[SCREENSIZE];
    unsigned blockloop, lineloop, rowloop;
    size_t result;

    if (argc > 1) {
        inp = fopen(argv[1], "rb");
        if (!inp)
            return EXIT_FAILURE;
    } else
        inp = stdin;

    result = fread(rawbits, SCREENSIZE, 1, inp);

    if (!result)
        return EXIT_FAILURE;

    if (argc > 1)
        fclose(inp);
    
    printf("P4\n256 192\n");

    for (blockloop = 0; blockloop < 3; blockloop++)
        for (lineloop = 0; lineloop < 8; lineloop++)
            for (rowloop = 0; rowloop < 8; rowloop++)
                fwrite(rawbits + (blockloop << 11) +
                       (lineloop << 5) + (rowloop << 8),
                       32, 1, stdout);

    return EXIT_SUCCESS;
}