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#include "Python.h"
#include <stdint.h>
/**
* @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
*/
uint32_t lfsr113(uint64_t **state)
{
// NOTE: This function *must* be the same as in the R package
uint64_t z1, z2, z3, z4;
uint64_t 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((uint32_t) 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(uint32_t seed, uint64_t **state)
{
// NOTE: This function *must* be the same as in the R package
uint64_t 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(uint64_t)*4);
}
(*state)[0] = z1;
(*state)[1] = z2;
(*state)[2] = z3;
(*state)[3] = z4;
}
/*
*
* Start of Python code
*
*/
static PyObject *_syncrng_seed(PyObject *self, PyObject *args)
{
uint32_t seed;
uint64_t *state = NULL;
PyObject *dblObj;
if (!PyArg_ParseTuple(args, "O", &dblObj))
return NULL;
seed = (uint32_t) PyLong_AsLong(dblObj);
lfsr113_seed(seed, &state);
PyObject *pystate = Py_BuildValue("[d, d, d, d, d]",
(double) state[0],
(double) state[1],
(double) state[2],
(double) state[3],
-1.0);
free(state);
return pystate;
}
static PyObject *_syncrng_rand(PyObject *self, PyObject *args)
{
int i;
uint32_t rand;
uint64_t *localstate = malloc(sizeof(uint64_t) * 4);
PyObject *listObj;
PyObject *dblObj;
if (!PyArg_ParseTuple(args, "O!", &PyList_Type, &listObj))
return NULL;
for (i=0; i<4; i++) {
dblObj = PyList_GetItem(listObj, i);
localstate[i] = (uint64_t) PyFloat_AS_DOUBLE(dblObj);
}
rand = lfsr113(&localstate);
PyObject *pystate = Py_BuildValue("[d, d, d, d, d]",
(double) localstate[0],
(double) localstate[1],
(double) localstate[2],
(double) localstate[3],
(double) 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}
};
static struct PyModuleDef moduledef = {
PyModuleDef_HEAD_INIT,
"_syncrng",
"Python interface to SyncRNG",
-1,
SyncRNGMethods,
NULL,
NULL,
NULL,
NULL
};
static PyObject *
moduleinit(void)
{
PyObject *m;
m = PyModule_Create(&moduledef);
return m;
}
PyMODINIT_FUNC
PyInit__syncrng(void)
{
return moduleinit();
}
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