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#include <stdint.h>
// Copy of Mersenne Twister, originally from Wikipedia
// https://github.com/bmurray7/mersenne-twister-examples
// Define MT19937 constants (32-bit RNG)
enum
{
// Assumes W = 32 (omitting this)
N = 624,
M = 397,
R = 31,
A = 0x9908B0DF,
F = 1812433253,
U = 11,
// Assumes D = 0xFFFFFFFF (omitting this)
S = 7,
B = 0x9D2C5680,
T = 15,
C = 0xEFC60000,
L = 18,
MASK_LOWER = (1ull << R) - 1,
MASK_UPPER = (1ull << R)
};
static uint32_t mt[N];
static uint16_t index;
// Re-init with a given seed
void RandomInit(const uint32_t seed) {
uint32_t i;
mt[0] = seed;
for ( i = 1; i < N; i++) {
mt[i] = (F * (mt[i - 1] ^ (mt[i - 1] >> 30)) + i);
}
index = N;
}
static void Twist() {
uint32_t i, x, xA;
for ( i = 0; i < N; i++) {
x = (mt[i] & MASK_UPPER) + (mt[(i + 1) % N] & MASK_LOWER);
xA = x >> 1;
if (x & 0x1) {
xA ^= A;
}
mt[i] = mt[(i + M) % N] ^ xA;
}
index = 0;
}
// Obtain a 32-bit random number
uint32_t RandomU32() {
uint32_t y;
int i = index;
if (index >= N) {
Twist();
i = index;
}
y = mt[i];
index = i + 1;
y ^= (mt[i] >> U);
y ^= (y << S) & B;
y ^= (y << T) & C;
y ^= (y >> L);
return y;
}
uint64_t RandomU64() {
uint32_t a = RandomU32();
uint32_t b = RandomU32();
return ((uint64_t) a) << 32 | b;
}
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