Random.user {base} | R Documentation |
Function RNGkind
allows a user-coded random number
generator to be supplied. The details are give here.
A user-specified RNG is called from entry points in dynamically-loaded
compiled code. The user must supply the entry point
user_unif_rand
, which takes no arguments and returns a
pointer to a double. The example below will show the general
pattern.
Optionally, the user can supply the entry point user_unif_init
,
which is called with an unsigned int
argument when
RNGkind
(or set.seed
) is called, and is intended
to be used to initialize the user's RNG code. The argument is intended
to be used to set the ``seeds''; it is the seed
argument to
set.seed
or an essentially random seed if RNGkind
is called.
If only these functions are supplied, no information about the
generator's state is recorded in .Random.seed
. Optionally,
functions user_unif_nseed
and user_unif_seedloc
can be
supplied which are called with no arguments and should return pointers
to the number of ``seeds'' and to an integer array of ``seeds''. Calls
to GetRNGstate
and PutRNGstate
will then copy this array
to and from .Random.seed
.
As with all compiled code, mis-specifying these functions can crash R. Do include the `R_ext/Random.h' header file for type checking.
## Marsaglia's conguential PRNG #include <R_ext/Random.h> static Int32 seed; static double res; static int nseed = 1; double * user_unif_rand() { seed = 69069 * seed + 1; res = seed * 2.32830643653869e-10; return &res; } void user_unif_init(Int32 seed_in) { seed = seed_in; } int * user_unif_nseed() { return &nseed; } int * user_unif_seedloc() { return (int *) &seed; }