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The
function uses a non-linear additive feedback random number generator employing
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 random number
generator is very large, approximately 16*((2**31)-1). The have (almost)
the same calling sequence and initialization properties as The difference
is that produces a much less random sequence -- in fact, the low dozen bits
generated by rand go through a cyclic pattern. All the bits generated by
are usable. For example, will produce a random binary value. Unlike
does not return the old seed; the reason for this is that the amount of
state information used is much more than a single word. (Two other routines
are provided to deal with restarting/changing random number generators).
Like however, will by default produce a sequence of numbers that can
be duplicated by calling with as the seed. The routine allows a state
array, passed in as an argument, to be initialized for future use. The
size of the state array (in bytes) is used by 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 for the initialization (which specifies a starting point
for the random number sequence, and provides for restarting at the same
point) is also an argument. The function returns a pointer to the previous
state information array. Once a state has been initialized, the routine
provides for rapid switching between states. The function returns a pointer
to the previous state array; its argument state array is used for further
random number generation until the next call to or Once a state array
has been initialized, it may be restarted at a different point either by
calling (with the desired seed, the state array, and its size) or by calling
both (with the state array) and (with the desired seed). The advantage
of calling both and 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 generator is greater than 2**69 which should
be sufficient for most purposes.
Earl T. Cohen
If is called
with less than 8 bytes of state information, or if detects that the state
information has been garbled, error messages are printed on the standard
error output.
These functions appeared in
About 2/3
the speed of
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