1RANDOM(3) Linux Programmer's Manual RANDOM(3)
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6 random, srandom, initstate, setstate - random number generator
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9 #include <stdlib.h>
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11 long int random(void);
12 void srandom(unsigned int seed);
13 char *initstate(unsigned int seed, char *state, size_t n);
14 char *setstate(char *state);
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17 The random() function uses a non-linear additive feedback random number
18 generator employing a default table of size 31 long integers to return
19 successive pseudo-random numbers in the range from 0 to RAND_MAX. The
20 period of this random number generator is very large, approximately
21 16*((2**31)-1).
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23 The srandom() function sets its argument as the seed for a new sequence
24 of pseudo-random integers to be returned by random(). These sequences
25 are repeatable by calling srandom() with the same seed value. If no
26 seed value is provided, the random() function is automatically seeded
27 with a value of 1.
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29 The initstate() function allows a state array state to be initialized
30 for use by random(). The size of the state array n is used by init‐
31 state() to decide how sophisticated a random number generator it should
32 use — the larger the state array, the better the random numbers will
33 be. seed is the seed for the initialization, which specifies a start‐
34 ing point for the random number sequence, and provides for restarting
35 at the same point.
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37 The setstate() function changes the state array used by the random()
38 function. The state array state is used for random number generation
39 until the next call to initstate() or setstate(). state must first
40 have been initialized using initstate() or be the result of a previous
41 call of setstate().
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44 The random() function returns a value between 0 and RAND_MAX. The
45 srandom() function returns no value. The initstate() and setstate()
46 functions return a pointer to the previous state array, or NULL on
47 error.
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50 EINVAL A state array of less than 8 bytes was specified to initstate().
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53 Current "optimal" values for the size of the state array n are 8, 32,
54 64, 128, and 256 bytes; other amounts will be rounded down to the near‐
55 est known amount. Using less than 8 bytes will cause an error.
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58 4.3BSD, POSIX.1-2001.
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61 rand(3), srand(3)
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65GNU 2000-08-20 RANDOM(3)