// rand.c: Minimalistic random Byte generator. A quicker and dirtier replacement
// for /dev/urandom, because script alternatives like
// while true; do date +%s%N > date.tmp; sha512sum date.tmp >> foo.bar0; done
// with about 100 kB/s and
// while true; do echo $RANDOM >> foo.bar1; done
// with about 500 kB/s are much slower than /dev/urandom, which has about 3 MB/s
// with a 32 Bit kernel and 6 MB/s with a 64 Bit kernel.
// And for production of equally distributed bytes the filtering of the random numbers
// (for the first example) and conversion to binary is missing.
// An alternative is 
// openssl rand -out foo.bar2 100000000000000
// with a speed of about 20 MB/s.
//
// Compile this program e. g. with 
// cc -Wall -O3 -lm -o rand rand.c
//
// Example usage: 
// ./rand > file.bin
// Speed: About 50 MByte/s with a 2.2 GHz CPU and a HDD with 50 MB/s.
// Tuning with a printf which uses more than one Byte or using a union
// did not work; it did not get faster.
//
// Dr. Rolf Freitag 2009, License: GPL, Version 1.0

#include <stdlib.h>
#include <stdio.h>
#include <time.h>
#include <math.h>
#include <unistd.h>
#include <sys/types.h>

int main()
{
  int i = time(NULL);
  srand( (getuid() << 15) ^(getppid() << 10) ^(getpid() << 5) ^((int)sqrt(i)));
  for(;;)
  {
    i^=rand();
    printf("%c",(char)i);
    printf("%c",(char)(i>>8));
  }
  return 0;
}