/*
* Initialize a Mersenne Twist RNG from a 624-int seed.
*
* The 32-bit seeding routine given by Matsumoto and Nishimura has the
* drawback that there are only 2^32 different PRNG sequences that can be
* generated by calling that function. This function solves that problem by
* allowing a full 624*32-bit state to be given. (Note that 31 bits of the
* given state are ignored; see the paper for details.)
*
* Since an all-zero state would cause the PRNG to cycle, we detect
* that case and abort the program (silently, since there is no
* portable way to produce a message in both C and C++ environments).
* An alternative would be to artificially force the state to some
* known nonzero value. However, I feel that if the user is providing
* a full state, it's a bug to provide all zeros and we we shouldn't
* conceal the bug by generating apparently correct output.
*/
void mts_seedfull(
mt_state* state, /* State vector to initialize */
uint32_t seeds[MT_STATE_SIZE])
/* Seed array to start from */
{
int had_nz = 0; /* NZ if at least one NZ seen */
int i; /* Loop index */
for (i = 0; i < MT_STATE_SIZE; i++)
{
if (seeds[i] != 0)
had_nz = 1;
state->statevec[MT_STATE_SIZE - i - 1] = seeds[i];
}
if (!had_nz)
{
/*
* It would be nice to abort with a message. Unfortunately, fprintf
* isn't compatible with all implementations of C++. In the
* interest of C++ compatibility, therefore, we will simply abort
* silently. It will unfortunately be up to a programmer to run
* under a debugger (or examine the core dump) to discover the cause
* of the abort.
*/
/* abort(); */
return;
}
state->stateptr = MT_STATE_SIZE;
mts_mark_initialized(state);
}
/*
* 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);
}
/*
* 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);
}
/*
* Load state from a file. Returns NZ if the load succeeded.
*/
int mts_loadstate(
FILE* statefile, /* File to load from */
mt_state* state) /* State to be loaded */
{
int i; /* Next word to load */
/*
* Set the state to "uninitialized" in case the load fails.
*/
state->initialized = state->stateptr = 0;
for (i = MT_STATE_SIZE; --i >= 0; )
{
if (fscanf(statefile, "%" SCNu32, &state->statevec[i]) != 1)
return 0;
}
if (fscanf(statefile, "%d", &state->stateptr) != 1)
return 0;
/*
* The only validity checking we can do is to insist that the
* state pointer be valid.
*/
if (state->stateptr < 0 || state->stateptr > MT_STATE_SIZE)
{
state->stateptr = 0;
return 0;
}
mts_mark_initialized(state);
return 1;
}
int cvar_revalidate_handle(void *cvar_handle)
{
handle_t *h = (handle_t *) cvar_handle;
mts_mark_initialized(&h->state);
return 0;
}
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);
}
