/*
* Initialize a Mersenne Twist PRNG from a 32-bit seed, using
* Matsumoto and Nishimura's newer reference implementation (Jan. 9,
* 2002).
*/
void mts_seed32new(
mt_state* state, /* State vector to initialize */
uint32_t seed) /* 32-bit seed to start from */
{
int i; /* Loop index */
uint32_t nextval; /* Next value being calculated */
/*
* Fill the state vector using Knuth's PRNG. Be sure to mask down
* to 32 bits in case we're running on a machine with 64-bit
* ints.
*/
state->statevec[MT_STATE_SIZE - 1] = seed & 0xffffffffUL;
for (i = MT_STATE_SIZE - 2; i >= 0; i--)
{
nextval = state->statevec[i + 1] >> KNUTH_SHIFT;
nextval ^= state->statevec[i + 1];
nextval *= KNUTH_MULTIPLIER_NEW;
nextval += (MT_STATE_SIZE - 1) - i;
state->statevec[i] = nextval & 0xffffffffUL;
}
state->stateptr = MT_STATE_SIZE;
mts_mark_initialized(state);
/*
* Matsumoto and Nishimura's implementation refreshes the PRNG
* immediately after running the Knuth algorithm. This is
* probably a good thing, since Knuth's PRNG doesn't generate very
* good numbers.
*/
mts_refresh(state);
}
/*
* Save state to a file. The save format is compatible with Richard
* J. Wagner's format, although the details are different. Returns NZ
* if the save succeeded. Produces one very long line containing 625
* numbers.
*/
int mts_savestate(
FILE* statefile, /* File to save to */
mt_state* state) /* State to be saved */
{
int i; /* Next word to save */
if (!state->initialized)
mts_seed32(state, DEFAULT_SEED32_OLD);
/*
* Ensure the state pointer is valid.
*/
if (state->stateptr < 0 || state->stateptr > MT_STATE_SIZE)
{
fprintf(stderr,
"Mtwist internal: Trying to write invalid state pointer %d\n",
state->stateptr);
mts_refresh(state);
}
for (i = MT_STATE_SIZE; --i >= 0; )
{
if (fprintf(statefile, "%" PRIu32 " ", state->statevec[i]) < 0)
return 0;
}
if (fprintf(statefile, "%d\n", state->stateptr) < 0)
return 0;
return 1;
}
/*
* Initialize a Mersenne Twist PRNG from a 32-bit seed.
*
* According to Matsumoto and Nishimura's paper, the seed array needs to be
* filled with nonzero values. (My own interpretation is that there needs
* to be at least one nonzero value). They suggest using Knuth's PRNG from
* Line 25, Table 1, p.102, "The Art of Computer Programming," Vol. 2 (2nd
* ed.), 1981. I find that rather odd, since that particular PRNG is
* sensitive to having an initial seed of zero (there are many other PRNGs
* out there that have an additive component, so that a seed of zero does
* not generate a repeating-zero sequence). However, one thing I learned
* from reading Knuth is that you shouldn't second-guess mathematicians
* about PRNGs. Also, by following M & N's approach, we will be compatible
* with other implementations. So I'm going to stick with their version,
* with the single addition that a zero seed will be changed to their
* default seed.
*/
void mts_seed32(
mt_state* state, /* State vector to initialize */
uint32_t seed) /* 32-bit seed to start from */
{
int i; /* Loop index */
if (seed == 0)
seed = DEFAULT_SEED32_OLD;
/*
* Fill the state vector using Knuth's PRNG. Be sure to mask down
* to 32 bits in case we're running on a machine with 64-bit
* ints.
*/
state->statevec[MT_STATE_SIZE - 1] = seed & 0xffffffff;
for (i = MT_STATE_SIZE - 2; i >= 0; i--)
state->statevec[i] =
(KNUTH_MULTIPLIER_OLD * state->statevec[i + 1]) & 0xffffffff;
state->stateptr = MT_STATE_SIZE;
mts_mark_initialized(state);
/*
* Matsumoto and Nishimura's implementation refreshes the PRNG
* immediately after running the Knuth algorithm. This is
* probably a good thing, since Knuth's PRNG doesn't generate very
* good numbers.
*/
mts_refresh(state);
}
void mts_seed32new(
mt_state* state,
uint32_t seed)
{
int i;
uint32_t nextval;
state->statevec[MT_STATE_SIZE - 1] = seed & 0xffffffffUL;
for (i = MT_STATE_SIZE - 2; i >= 0; i--)
{
nextval = state->statevec[i + 1] >> KNUTH_SHIFT;
nextval ^= state->statevec[i + 1];
nextval *= KNUTH_MULTIPLIER_NEW;
nextval += (MT_STATE_SIZE - 1) - i;
state->statevec[i] = nextval & 0xffffffffUL;
}
state->stateptr = MT_STATE_SIZE;
mts_mark_initialized(state);
mts_refresh(state);
}
