[elektro] Véletlen az álvéletlennel

[Gál Zsolt]

//X ABC Algorithm Random Number Generator for 8-Bit Devices:
//This is a small PRNG, experimentally verified to have at least a 50
million byte period
//by generating 50 million bytes and observing that there were no
overapping sequences and repeats.
//This generator passes serial correlation, entropy , Monte Carlo Pi value,
arithmetic mean,
//And many other statistical tests. This generator may have a period of up
to 2^32, but this has
//not been verified.
//
// By XORing 3 bytes into the a,b, and c registers, you can add in entropy
from
//an external source easily.
//
//This generator is free to use, but is not suitable for cryptography due
to its short period(by //cryptographic standards) and simple construction.
No attempt was made to make this generator
// suitable for cryptographic use.
//
//Due to the use of a constant counter, the generator should be resistant
to latching up.
//A significant performance gain is had in that the x variable is nly ever
incremented.
//
//Only 4 bytes of ram are needed for the internal state, and generating a
byte requires 3 XORs , //2 ADDs, one bit shift right , and one increment.
Difficult or slow operations like multiply, etc
//were avoided for maximum speed on ultra low power devices.


init_rng(s1,s2,s3) //Can also be used to seed the rng with more entropy
during use.
{
//XOR new entropy into key state
a ^=s1;
b ^=s2;
c ^=s3;

x++;
a = (a^c^x);
b = (b+a);
c = (c+(b>>1)^a);
}

unsigned char randomize()
{
x++;               //x is incremented every round and is not affected by
any other variable
a = (a^c^x);       //note the mix of addition and XOR
b = (b+a);         //And the use of very few instructions
c = (c+(b>>1)^a);  //the right shift is to ensure that high-order bits from
b can affect
return(c)          //low order bits of other variables
}

2016. március 14. 21:09 Horvath Janos írta, <winnerbt at fibermail.hu>:

> Sziasztok!
> Random módon beleszaladtam egy álvéletlen problémába.
> Van olyan uC amiben HW módon van a hétköznapi
> shiftregiszteres+visszacsatolásos álvéletlen generátor?
> Persze egy komparátor nem ártana még mellé.
> A kimenet analóg lenne a végén.
> (O.k. SW-ből meg tudom csinálni, de az lassú.)
> JAni
> 21:08
>
> -----------------------------------------
>           elektro[-flame|-etc]
>



-- 
~~~~~~~~~~~~~~~~
http://galzsolt.zzl.org