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28 .\" @(#)random.3 8.1 (Berkeley) 6/4/93
40 .Nd non-cryptographic pseudorandom number generator; routines for changing generators
48 .Fn srandom "unsigned int seed"
52 .Fn initstate "unsigned int seed" "char *state" "size_t n"
54 .Fn setstate "char *state"
57 The functions described in this manual page are not secure.
58 Applications which require unpredictable random numbers should use
63 Unless initialized with less than 32 bytes of state, the
66 uses a non-linear additive feedback random number generator employing a
67 default table of size 31 long integers to return successive pseudo-random
68 numbers in the range from 0 to
69 .if t 2\u\s731\s10\d\(mi1.
71 The period of this random number generator is very large, approximately
72 .if t 16\(mu(2\u\s731\s10\d\(mi1).
73 .if n 16*((2**31)\(mi1).
75 If initialized with less than 32 bytes of state,
77 uses the poor-quality 32-bit Park-Miller LCG.
83 functions are analagous to
91 is implicitly initialized as if
93 had been invoked explicitly.
97 routine initializes the state array using random numbers obtained from the
99 This can generate states which are impossible to reproduce by calling
101 because the succeeding terms in the state buffer are no longer derived from the
102 Park-Miller LCG algorithm applied to a fixed seed.
106 routine initializes the provided state array of
108 values and uses it in future
115 the underlying object must be a naturally aligned array of 32-bit values.)
116 The size of the state array (in bytes) is used by
118 to decide how sophisticated a random number generator it should use \(em the
119 more state, the better the random numbers will be.
120 (Current "optimal" values for the amount of state information are
121 8, 32, 64, 128, and 256 bytes; other amounts will be rounded down to
122 the nearest known amount.
123 Using less than 8 bytes will cause an error.)
131 returns a pointer to the previous state information array.
137 to using the provided state.
138 It returns a pointer to the previous state.
140 Once a state array has been initialized, it may be restarted at a
141 different point either by calling
143 (with the desired seed, the state array, and its size) or by calling
146 (with the state array) and
148 (with the desired seed).
149 The advantage of calling both
153 is that the size of the state array does not have to be remembered after
156 With 256 bytes of state information, the period of the random number
157 generator is greater than
158 .if t 2\u\s769\s10\d,
160 which should be sufficient for most purposes.
164 is called with less than 8 bytes of state information, or if
166 detects that the state information has been garbled,
175 functions appeared in