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/* -*- Mode: C++ -*- */
/* This is public-domain Mersenne Twister code,
* attributed to Michael Brundage. Thanks!
* http://www.qbrundage.com/michaelb/pubs/essays/random_number_generation.html
*/
#undef MT_LEN
#undef MT_IA
class MTRandom {
public:
enum Constants {
MT_LEN = 624,
MT_IA = 397
};
static const uint32_t TEST_SEED1;
static const uint32_t UPPER_MASK;
static const uint32_t LOWER_MASK;
static const uint32_t MATRIX_A;
MTRandom() {
Init(TEST_SEED1);
}
explicit MTRandom(uint32_t seed) {
Init(seed);
}
uint32_t Rand32 () {
uint32_t y;
static unsigned long mag01[2] = {
0 , MATRIX_A
};
if (mt_index_ >= MT_LEN) {
int kk;
for (kk = 0; kk < MT_LEN - MT_IA; kk++) {
y = (mt_buffer_[kk] & UPPER_MASK) | (mt_buffer_[kk + 1] & LOWER_MASK);
mt_buffer_[kk] = mt_buffer_[kk + MT_IA] ^ (y >> 1) ^ mag01[y & 0x1UL];
}
for (;kk < MT_LEN - 1; kk++) {
y = (mt_buffer_[kk] & UPPER_MASK) | (mt_buffer_[kk + 1] & LOWER_MASK);
mt_buffer_[kk] = mt_buffer_[kk + (MT_IA - MT_LEN)] ^ (y >> 1) ^ mag01[y & 0x1UL];
}
y = (mt_buffer_[MT_LEN - 1] & UPPER_MASK) | (mt_buffer_[0] & LOWER_MASK);
mt_buffer_[MT_LEN - 1] = mt_buffer_[MT_IA - 1] ^ (y >> 1) ^ mag01[y & 0x1UL];
mt_index_ = 0;
}
y = mt_buffer_[mt_index_++];
y ^= (y >> 11);
y ^= (y << 7) & 0x9d2c5680UL;
y ^= (y << 15) & 0xefc60000UL;
y ^= (y >> 18);
return y;
}
uint32_t ExpRand32(uint32_t mean) {
double mean_d = mean;
double erand = log (1.0 / (Rand32() / (double)UINT32_MAX));
uint32_t x = (uint32_t) (mean_d * erand + 0.5);
return x;
}
uint64_t Rand64() {
return ((uint64_t)Rand32() << 32) | Rand32();
}
uint64_t ExpRand64(uint64_t mean) {
double mean_d = mean;
double erand = log (1.0 / (Rand64() / (double)UINT32_MAX));
uint64_t x = (uint64_t) (mean_d * erand + 0.5);
return x;
}
template <typename T>
T Rand() {
switch (sizeof(T)) {
case sizeof(uint32_t):
return Rand32();
case sizeof(uint64_t):
return Rand64();
default:
cerr << "Invalid sizeof T" << endl;
abort();
}
}
template <typename T>
T ExpRand(T mean) {
switch (sizeof(T)) {
case sizeof(uint32_t):
return ExpRand32(mean);
case sizeof(uint64_t):
return ExpRand64(mean);
default:
cerr << "Invalid sizeof T" << endl;
abort();
}
}
private:
void Init(uint32_t seed) {
mt_buffer_[0] = seed;
mt_index_ = MT_LEN;
for (int i = 1; i < MT_LEN; i++) {
/* See Knuth TAOCP Vol2. 3rd Ed. P.106 for multiplier. */
/* In the previous versions, MSBs of the seed affect */
/* only MSBs of the array mt[]. */
/* 2002/01/09 modified by Makoto Matsumoto */
mt_buffer_[i] =
(1812433253UL * (mt_buffer_[i-1] ^ (mt_buffer_[i-1] >> 30)) + i);
}
}
int mt_index_;
uint32_t mt_buffer_[MT_LEN];
};
const uint32_t MTRandom::TEST_SEED1 = 5489UL;
const uint32_t MTRandom::UPPER_MASK = 0x80000000;
const uint32_t MTRandom::LOWER_MASK = 0x7FFFFFFF;
const uint32_t MTRandom::MATRIX_A = 0x9908B0DF;
class MTRandom8 {
public:
MTRandom8(MTRandom *rand)
: rand_(rand) {
}
uint8_t Rand8() {
uint32_t r = rand_->Rand32();
// TODO: make this use a single byte at a time?
return (r & 0xff) ^ (r >> 7) ^ (r >> 15) ^ (r >> 21);
}
private:
MTRandom *rand_;
};
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