random(3M)																random(3M)

NAME
random(), srandom(), initstate(), setstate() - generate a pseudorandom number
SYNOPSIS
DESCRIPTION
The and functions are random-number generators that have virtually the same calling sequence and initialization properties as the and func- tions, but produce sequences that are more random. The low 12 bits generated by the function go through a cyclic pattern, while all the bits generated by the function are usable. For example, produces a random binary value. The function uses a nonlinear additive feedback random-number generator employing a default state array size of 31 long integers to return successive pseudorandom numbers in the range from 0 to The period of this random-number generator is approximately 16 x The size of the state array determines the period of the random-number generator. Increasing the state array size increases the period. With 256 bytes of state information, the period of the random-number generator is greater than Like the function, the function produces by default a sequence of numbers that can be duplicated by calling the function with a value of 1 as the seed. The function initializes the current state array using the value of seed. The and functions handle restarting and changing random-number generators. The function allows a state array, pointed to by the state argument, to be initialized for future use. The size argument, which specifies the size in bytes of the state array, is used by the func- tion to decide how sophisticated a random-number generator to use; the larger the state array, the more random the numbers. Values for the amount of state information are 8, 32, 64, 128, and 256 bytes. Amounts less than 8 bytes return a NULL pointer, while other amounts are rounded down to the nearest known value. The seed argument specifies a starting point for the random-number sequence and provides for restarting at the same point. The function returns a pointer to the previous state information array. Once a state has been initialized, the function allows switching between state arrays. The array defined by the state argument is used for further random-number generation until the function is called or the function is called again. The function returns a pointer to the pre- vious state array. After initialization, a state array can be restarted at a different point in one of two ways: The function can be used, with the desired seed, state array, and size of the array. The function, with the desired state, can be used, followed by the function with the desired seed. The advantage of using both of these functions is that the size of the state array does not have to be saved once it is initialized.
RETURN VALUE
The function returns the generated pseudorandom number. The function returns no value. Upon successful completion, the and functions return a pointer to the previous state array. Otherwise, a NULL pointer is returned.
ERRORS
If the function detects that the state information has been damaged, error messages are written to standard error.
SEE ALSO
drand48(3C), rand(3C), random(7).
STANDARDS CONFORMANCE
random(3M)

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