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

const unsigned int MY_RAND_MAX = ~0;  /* 2 ^ sizeof(unsigned int) - 1 */
const unsigned int HOW_MANY    = 1000000;
const char *FILE_NAME          = "out.rnd";

/*
  Last updated: Thu Aug 4 2005

  This code was written to show how to extract pseudo-random
  numbers in the range [0, 1) from a random file. Each number
  will require sizeof(unsigned int) bytes from the file.

  Should I use just 2 bytes instead? I guess I should.

  The last version should be here:
  http://www.geocities.com/arhuaco/log/src/file2prng.c

  It computes the average of 1000000 (HOW_MANY) numbers.
  The mean should be close to 1/2 in a random sequence.

  You can generate such pseudo-random file with the program rng1.c.
  You can download the source of this generator from:

  http://www.geocities.com/arhuaco/log/src/rng1.c

  Compile with:

  $ gcc file2prng.c  -O2 -o file2prng

  Complete usage example:

  $ wget http://www.geocities.com/arhuaco/log/src/rng1.c
  $ gcc rng1.c -o rng1
  $ ./rng1 172245973
  $ gcc file2prng.c  -O2 -o file2prng
  $ ./file2prng
    average is 0.499691

  TODO: Build a generator that uses a cellular atomaton in memory.
        This is the right way to do it.
*/

long double pseudo_random (FILE *);

int
main(int argc, char *argv[])
{
  FILE *p;
  int i;
  long double sum;

  p = fopen(FILE_NAME, "rb");

  if (!p)
  {
    fprintf(stderr, "I could not open file %s\n", FILE_NAME);
    exit(EXIT_FAILURE);
  }

  sum = 0.0L;

  for (i = 0; i < HOW_MANY; ++i) 
  {
    long double number;

    number = pseudo_random(p);
    /* printf ("%.10Lg\n", number); */

    sum += number;
  }

  printf("average is %Lg\n", sum / HOW_MANY);

  fclose(p);

  return EXIT_SUCCESS;
}

long double
pseudo_random (FILE *p)
{
  unsigned int number;
  int actually_read;

  actually_read = fread(&number, sizeof(unsigned int), 1, p);

  if (actually_read != 1)
  {
    fprintf(stderr, "I coul'd read %d bytes from the stream. Sorry.\n", sizeof(unsigned int));
    exit(EXIT_FAILURE);
  }

  if (number == MY_RAND_MAX) /* Should I use less bits? Perhaps 16? */
    number --;

  return (long double)number / (long double)MY_RAND_MAX;
}