What's the internal state size and output range of mrg32k3a?

Question

This is Pierre L'Ecuyer's PRNG. I know its period is $2^{191}$, but I don't know what is its internal state size. What is it?

Answer 1

The answer is based on the given period construction from your link.

You have to store the two modulus

• $m_1 = 2^{32} − 209 = 4294967087$ and
• $m_2 = 2^{32} − 22853 = 4294944443,$

and the internal states are;

• $s_{1,n} = \{x_{1,n},x_{1,n+1}, x_{1,n+1} \}$ and
• $s_{2,n} = \{x_{2,n},x_{2,n+1}, x_{2,n+1} \}$.

The $z_n = (x_{1,n}- x_{2,n}) \bmod m_1$, evolves with this $x_{1,n}$ and $x_{2,n}$ where each requrrence relation for $x_{1,n}$ and $x_{2,n}$ is taken module $m_1$ and $m_2$, respectively;

$$x_{1,n} = (1403580 \times x_{1,n-2} - 810728 \times x_{1,n-3} ) \bmod m_1,$$ $$x_{2,n} = (527612 \times x_{2,n-2} -1370589 \times x_{2,n-3} ) \bmod m_2$$

Therefore you need to store 3 moduli $m_1$ and 3 moduli $m_2$ internal states.

The $m_1$ and $m_2$ is very close to $2^{32}$, so we can say that you need;

• 6 unsigned 32-bit integers for the internal states.
• For the modulus, you will also need 2 unsigned 32-bit integers.

the range is $m_1$ since the $z_n$ is taken $\mod m_1$.

Yes; the state for all practical purposes is $8 \cdot 32=256$-bit.