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RANDOM(3)	       FreeBSD Library Functions Manual		     RANDOM(3)

NAME
     random, srandom, srandomdev, initstate, setstate -- non-cryptographic
     pseudorandom number generator; routines for changing generators

LIBRARY
     Standard C	Library	(libc, -lc)

SYNOPSIS
     #include <stdlib.h>

     long
     random(void);

     void
     srandom(unsigned int seed);

     void
     srandomdev(void);

     char *
     initstate(unsigned	int seed, char *state, size_t n);

     char *
     setstate(char *state);

DESCRIPTION
     The functions described in	this manual page are not secure.  Applications
     which require unpredictable random	numbers	should use arc4random(3) in-
     stead.

     Unless initialized	with less than 32 bytes	of state, the random() func-
     tion uses a non-linear additive feedback random number generator employ-
     ing 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 ran-
     dom number	generator is very large, approximately 16*((2**31)-1).

     If	initialized with less than 32 bytes of state, random() uses the	poor-
     quality 32-bit Park-Miller	LCG.

     The random() and srandom()	functions are analagous	to rand(3) and
     srand(3).

     Like rand(3), random() is implicitly initialized as if srandom(1) had
     been invoked explicitly.

     The srandomdev() routine initializes the state array using	random numbers
     obtained from the kernel.	This can generate states which are impossible
     to	reproduce by calling srandom(),	because	the succeeding terms in	the
     state buffer are no longer	derived	from the Park-Miller LCG algorithm ap-
     plied to a	fixed seed.

     The initstate() routine initializes the provided state array of uint32_t
     values and	uses it	in future random() invocations.	 (Despite the char *
     type of state, the	underlying object must be a naturally aligned array of
     32-bit values.)  The size of the state array (in bytes) is	used by
     initstate() to decide how sophisticated a random number generator it
     should use	-- the more state, the better the random numbers will be.
     (Current "optimal"	values for the amount of state information are 8, 32,
     64, 128, and 256 bytes; other amounts will	be rounded down	to the nearest
     known amount.  Using less than 8 bytes will cause an error.)  The seed is
     used as in	srandom().  The	initstate() function returns a pointer to the
     previous state information	array.

     The setstate() routine switches random() to using the provided state.  It
     returns a pointer to the previous state.

     Once a state array	has been initialized, it may be	restarted at a differ-
     ent point either by calling initstate() (with the desired seed, the state
     array, and	its size) or by	calling	both setstate()	(with the state	array)
     and srandom() (with the desired seed).  The advantage of calling both
     setstate()	and srandom() is that the size of the state array does not
     have to be	remembered after it is initialized.

     With 256 bytes of state information, the period of	the random number gen-
     erator is greater than 2**69 which	should be sufficient for most pur-
     poses.

DIAGNOSTICS
     If	initstate() is called with less	than 8 bytes of	state information, or
     if	setstate() detects that	the state information has been garbled,	NULL
     is	returned.

SEE ALSO
     arc4random(3), lrand48(3),	rand(3), random(4)

HISTORY
     These functions appeared in 4.2BSD.

AUTHORS
     Earl T. Cohen

FreeBSD	13.0		       February	1, 2020			  FreeBSD 13.0

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | DIAGNOSTICS | SEE ALSO | HISTORY | AUTHORS

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