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28 .\" @(#)random.3 8.1 (Berkeley) 6/4/93
39 .Nd non-cryptographic pseudorandom number generator; routines for changing generators
47 .Fn srandom "unsigned int seed"
51 .Fn initstate "unsigned int seed" "char *state" "size_t n"
53 .Fn setstate "char *state"
56 The functions described in this manual page are not secure.
57 Applications which require unpredictable random numbers should use
62 Unless initialized with less than 32 bytes of state, the
65 uses a non-linear additive feedback random number generator employing a
66 default table of size 31 long integers to return successive pseudo-random
67 numbers in the range from 0 to
68 .if t 2\u\s731\s10\d\(mi1.
70 The period of this random number generator is very large, approximately
71 .if t 16\(mu(2\u\s731\s10\d\(mi1).
72 .if n 16*((2**31)\(mi1).
74 If initialized with less than 32 bytes of state,
76 uses the poor-quality 32-bit Park-Miller LCG.
82 functions are analagous to
90 is implicitly initialized as if
92 had been invoked explicitly.
96 routine initializes the state array using random numbers obtained from the
98 This can generate states which are impossible to reproduce by calling
100 because the succeeding terms in the state buffer are no longer derived from the
101 Park-Miller LCG algorithm applied to a fixed seed.
105 routine initializes the provided state array of
107 values and uses it in future
114 the underlying object must be a naturally aligned array of 32-bit values.)
115 The size of the state array (in bytes) is used by
117 to decide how sophisticated a random number generator it should use \(em the
118 more state, the better the random numbers will be.
119 (Current "optimal" values for the amount of state information are
120 8, 32, 64, 128, and 256 bytes; other amounts will be rounded down to
121 the nearest known amount.
122 Using less than 8 bytes will cause an error.)
130 returns a pointer to the previous state information array.
136 to using the provided state.
137 It returns a pointer to the previous state.
139 Once a state array has been initialized, it may be restarted at a
140 different point either by calling
142 (with the desired seed, the state array, and its size) or by calling
145 (with the state array) and
147 (with the desired seed).
148 The advantage of calling both
152 is that the size of the state array does not have to be remembered after
155 With 256 bytes of state information, the period of the random number
156 generator is greater than
157 .if t 2\u\s769\s10\d,
159 which should be sufficient for most purposes.
163 is called with less than 8 bytes of state information, or if
165 detects that the state information has been garbled,
174 functions appeared in