// $Id: filler.c 2445 2007-04-20 01:07:22Z flaterco $
// Data source for overwriting a disk.
// gcc -Wall -Wextra -O2 -static -s -o filler filler.c

#define __STDC_FORMAT_MACROS
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <inttypes.h>
#include <assert.h>
#include <time.h>

void usage () {
  fprintf (stderr, "Usage: filler [0|1|F0|0F|R]\n");
  fprintf (stderr, "  0 = generate zeros\n");
  fprintf (stderr, "  1 = generate ones\n");
  fprintf (stderr, "  F0 = generate character F0\n");
  fprintf (stderr, "  0F = generate character 0F\n");
  fprintf (stderr, "  R = generate cheap pseudorandom bits\n");
  exit (-1);
}

uint32_t pseudorand () {
  // Other than not getting a blatantly repetitive pattern, I don't
  // really care how random it is.  It just needs to be fast.
  // /dev/urandom is too slow.

  // On Linux, the low-order bits of rand() are supposedly as good as
  // the high-order ones (according to man rand).  However, RAND_MAX
  // is 2147483647.  We need one more bit.

  uint32_t r = rand();
  if (rand() & 1)
    r = ~r;
  return r;
}

int main (int argc, char **argv) {
  uintmax_t bcount = 0;

  if (argc != 2)
    usage ();

  if (!strcmp (argv[1], "0")) {
    while (putchar (0) != EOF)
      ++bcount;
  } else if (!strcmp (argv[1], "1")) {
    while (putchar (0xFF) != EOF)
      ++bcount;
  } else if (!strcmp (argv[1], "F0")) {
    while (putchar (0xF0) != EOF)
      ++bcount;
  } else if (!strcmp (argv[1], "0F")) {
    while (putchar (0x0F) != EOF)
      ++bcount;
  } else if (!strcmp (argv[1], "R")) {

    assert (RAND_MAX == 2147483647); // portability be damned.
    assert (sizeof(uint32_t) == 4);
    srand (time(NULL));

    uint32_t word = pseudorand();
    while (fwrite (&word, 4, 1, stdout) == 1) {
      bcount += 4;
      word = pseudorand();
    }

  } else {
    usage ();
  }

  fprintf (stderr, "%" PRIuMAX " bytes written\n", bcount);
  return 0;
}