// $Id: filler.cc 3733 2010-08-10 23:31:29Z flaterco $
// Data source for overwriting a disk.
// g++ -Wall -Wextra -O2 -static -s -o filler filler.cc

#define __STDC_FORMAT_MACROS
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <inttypes.h>
#include <cassert>
#include <vector>
#include <boost/random.hpp>

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);
}

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")) {

    // The goal is to generate terabytes of nonrepeating pseudorandom data at
    // or above the speed at which it can be written to a hard drive.
    // /dev/urandom is too slow (5.9 MB/s on a 3.6 GHz P4).  random() has a
    // period of approximately 16 * ((2^31) - 1) and generates 31 bits per
    // invocation, so you get at most 133 GB before it repeats.  This one has
    // a period of approximately 2^2300000, generates 48 bits per invocation,
    // and produces about 21 MB/s on a 3.6 GHz P4 (still too slow).  It uses
    // at least 356 kB of memory for state.

    static const uint32_t seedSize = 44497 * 2;
    std::vector<uint32_t> seed (seedSize);
    FILE *fp = fopen ("/dev/urandom", "r");
    assert (fp);
    assert (fread (&(seed[0]), sizeof(uint32_t), seedSize, fp) == seedSize);
    fclose (fp);
    std::vector<uint32_t>::iterator itref (seed.begin());
    boost::lagged_fibonacci44497 boostFibRng (itref, seed.end());
    boost::uniform_int<uint64_t> boostFibDist (0ULL, 0xFFFFFFFFFFFFULL);
    boost::variate_generator<boost::lagged_fibonacci44497&,
      boost::uniform_int<uint64_t> > pseudorand (boostFibRng, boostFibDist);

    uint64_t word = pseudorand();
    while (fwrite (&word, 6, 1, stdout) == 1) {
      bcount += 6;
      word = pseudorand();
    }

  } else {
    usage ();
  }

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