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arc4rand, arc4random, random, read_random, srandom - supply pseudo-random



      arc4rand, arc4random, random, read_random, srandom - supply pseudo-random


      #include <sys/libkern.h>
      srandom(u_long seed);
      arc4rand(void *ptr, u_int length, int reseed);
      #include <sys/random.h>
      read_random(void *buffer, int count);


      The random() function will by default produce a sequence of numbers that
      can be duplicated by calling srandom() with ‘1’ as the seed.  The
      srandom() function may be called with any arbitrary seed value to get
      slightly more unpredictable numbers.  It is important to remember that
      the random() function is entirely predictable, and is therefore not of
      use where knowledge of the sequence of numbers may be of benefit to an
      The arc4rand() function will return very good quality random numbers,
      slightly better suited for security-related purposes.  The random numbers
      from arc4rand() are seeded from the entropy device if it is available.
      Automatic reseeds happen after a certain timeinterval and after a certain
      number of bytes have been delivered.  A forced reseed can be forced by
      passing a non-zero value in the reseed argument.
      The read_random() function is used to return entropy directly from the
      entropy device if it has been loaded.  If the entropy device is not
      loaded, then the buffer is filled with output generated by random().  The
      buffer is filled with no more than count bytes.  It is advised that
      read_random() is not used; instead use arc4rand()
      All the bits generated by random(), arc4rand() and read_random() are
      usable.  For example, ‘random()&01’ will produce a random binary value.
      The arc4random() is a convenience function which calls arc4rand() to
      return a 32 bit pseudo-random integer.
      The random() function uses a non-linear additive feedback random number
      generator employing a default table of size 31 long integers to return
      successive pseudo-random numbers in the range from 0 to (2**31)−1.  The
      period of this random number generator is very large, approximately
      The arc4rand() function uses the RC4 algorithm to generate successive
      pseudo-random bytes.  The arc4random() function uses arc4rand() to gener‐
      ate pseudo-random numbers in the range from 0 to (2**32)−1.
      The read_random() function returns the number of bytes placed in buffer.


      Dan Moschuk wrote arc4random().
      Mark R V Murray wrote read_random().


Based on BSD UNIX
FreeBSD is an advanced operating system for x86 compatible (including Pentium and Athlon), amd64 compatible (including Opteron, Athlon64, and EM64T), UltraSPARC, IA-64, PC-98 and ARM architectures. It is derived from BSD, the version of UNIX developed at the University of California, Berkeley. It is developed and maintained by a large team of individuals. Additional platforms are in various stages of development.