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#ifdef TARGETPYTHON
#include "Python.h"
#endif
#ifndef TARGETPYTHON
#define STRICT_R_HEADERS
#include <stdio.h>
#include <stdlib.h>
#include <R.h>
#include <Rinternals.h>
#endif
/**
* @brief Generate a single random number using the capped Tausworthe RNG
*
* @details
* This generates random numbers according to the process described in [1]. As
* an additional step, the resulting random number is capped to 0xFFFFFFFF
* using a bitwise and. This is done to yield the range [0, 2^32-1]. On
* return, the state variables are updated.
*
* [1]: @article{l1996maximally,
* title={Maximally equidistributed combined Tausworthe generators},
* author={L’ecuyer, Pierre},
* journal={Mathematics of Computation of the American Mathematical
* Society},
* volume={65},
* number={213},
* pages={203--213},
* year={1996}
* }
*
* @param[in,out] state pointer to current state array
*
* @return a generated random number
*/
unsigned long lfsr113(unsigned long **state)
{
unsigned long z1, z2, z3, z4, b;
z1 = (*state)[0];
z2 = (*state)[1];
z3 = (*state)[2];
z4 = (*state)[3];
b = (((z1 << 6) ^ z1) >> 13);
z1 = (((z1 & 4294967294) << 18) ^ b);
b = (((z2 << 2) ^ z2) >> 27);
z2 = (((z2 & 4294967288) << 2) ^ b);
b = (((z3 << 13) ^ z3) >> 21);
z3 = (((z3 & 4294967280) << 7) ^ b);
b = (((z4 << 3) ^ z4) >> 12);
z4 = (((z4 & 4294967168) << 13) ^ b);
b = (z1 ^ z2 ^ z3 ^ z4);
(*state)[0] = z1;
(*state)[1] = z2;
(*state)[2] = z3;
(*state)[3] = z4;
b = b & 0xFFFFFFFF;
return(b);
}
/**
* @brief Seed the Tausworthe RNG using a seed value
*
* @details
* This function seeds the state array using a supplied seed value. As noted
* in [1] (see lfsr113()), the values of z1, z2, z3, and z4 should be larger
* than 1, 7, 15, and 127 respectively.
*
* @param[in] seed user supplied seed value for the RNG
* @param[out] state state of the RNG
*/
void lfsr113_seed(unsigned long seed, unsigned long **state)
{
unsigned long z1 = 2,
z2 = 8,
z3 = 16,
z4 = 128;
z1 = (z1 * (seed + 1));
z2 = (z2 * (seed + 1));
z3 = (z3 * (seed + 1));
z4 = (z4 * (seed + 1));
z1 = (z1 > 1) ? z1 : z1 + 1;
z2 = (z2 > 7) ? z2 : z2 + 7;
z3 = (z3 > 15) ? z3 : z3 + 15;
z4 = (z4 > 127) ? z4 : z4 + 127;
if (*state == NULL) {
(*state) = malloc(sizeof(unsigned long)*4);
}
(*state)[0] = z1;
(*state)[1] = z2;
(*state)[2] = z3;
(*state)[3] = z4;
}
#ifdef TARGETPYTHON
/*
*
* Start of Python code
*
*/
static PyObject *syncrng_seed(PyObject *self, PyObject *args)
{
unsigned long seed, *state = NULL;
if (!PyArg_ParseTuple(args, "k", &seed))
return NULL;
lfsr113_seed(seed, &state);
PyObject *pystate = Py_BuildValue("[k, k, k, k]",
state[0], state[1], state[2], state[3]);
free(state);
return pystate;
}
static PyObject *syncrng_rand(PyObject *self, PyObject *args)
{
unsigned long i, value, numints, *localstate;
PyObject *listObj;
PyObject *intObj;
if (!PyArg_ParseTuple(args, "O!", &PyList_Type, &listObj))
return NULL;
// we're just assuming you would never pass more than 4 values
localstate = malloc(sizeof(unsigned long)*5);
numints = PyList_Size(listObj);
for (i=0; i<numints; i++) {
intObj = PyList_GetItem(listObj, i);
value = (unsigned long) PyLong_AsLong(intObj);
localstate[i] = value;
}
unsigned long rand = lfsr113(&localstate);
localstate[4] = rand;
PyObject *pystate = Py_BuildValue("[k, k, k, k, k]",
localstate[0], localstate[1], localstate[2],
localstate[3], rand);
free(localstate);
return pystate;
}
static PyMethodDef SyncRNGMethods[] = {
{"seed", syncrng_seed, METH_VARARGS,
"Seed the RNG."},
{"rand", syncrng_rand, METH_VARARGS,
"Generate a single random integer using SyncRNG."},
{NULL, NULL, 0, NULL}
};
PyMODINIT_FUNC initsyncrng(void)
{
PyObject *m = Py_InitModule3("syncrng", SyncRNGMethods,
"Python interface to SyncRNG");
if (m == NULL)
return;
}
#endif
#ifndef TARGETPYTHON
/*
*
* Start of R code
*
*/
SEXP R_syncrng_seed(SEXP seed)
{
int i;
double *pseed = REAL(seed),
*pstate = NULL;
unsigned long useed = (unsigned long) *pseed;
unsigned long *state = NULL;
lfsr113_seed(useed, &state);
SEXP Rstate = PROTECT(allocVector(REALSXP, 5));
pstate = REAL(Rstate);
for (i=0; i<4; i++) {
pstate[i] = (double) state[i];
}
pstate[4] = -1.0;
free(state);
UNPROTECT(1);
return Rstate;
}
SEXP R_syncrng_rand(SEXP state)
{
unsigned long *localstate = malloc(sizeof(unsigned long)*4);
double *pstate = REAL(state);
int i;
for (i=0; i<4; i++) {
localstate[i] = (unsigned long) pstate[i];
}
unsigned long rand = lfsr113(&localstate);
SEXP Rstate = PROTECT(allocVector(REALSXP, 5));
pstate = REAL(Rstate);
for (i=0; i<4; i++) {
pstate[i] = (double) localstate[i];
}
pstate[4] = (double) rand;
UNPROTECT(1);
free(localstate);
return Rstate;
}
/*
*
* End of R code
*
*/
#endif
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