Seedable RNG?

Does anyone have a seedable Random Number Generator routine in LSL? I'd like a way to generate the same set of "random" numbers every time based off a given seed value.

Hewee Zetkin kindly provided me with this when I asked.

integer SeededRand(string Seed)
{
string Hash = llMD5String(Seed);
integer I1 = (integer)("0x"+llGetSubString(Hash, 0, 7));
integer I2 = (integer)("0x"+llGetSubString(Hash, 8, 15));
integer I3 = (integer)("0x"+llGetSubString(Hash, 16, 23));
integer I4 = (integer)("0x"+llGetSubString(Hash, 24, 31));
return I1^I2^I3^I4;
}

Typed from memory so it may need syntax fixes.

EDIT: Of course, you can stick any other string manipulation you'd like on the Seed if you want to make the generator a little more in depth... As for making it within a specific range, I wouldn't know where to start. XD

EDIT2: It uses MD5String because I needed to generate based on an AV UUID when I asked for a Seedable PsuedoRandom. The same Concept of making integers from MD5String Bits also works for generating strings, though its better to XOR 2 Seed Strings for that.

Caveat: I've translated this from a different programming language - one where floats have a defined precision, and can actually be relied on - so, I'm not completely confident that LSL math is accurate enough to give a true result. However, it superficially seems to work. I leave it to anyone who is interested (and more knowledgeable than me) to test if the numbers pass some kind of pseudo random number test.

In any case, following a script reset, and for a given seed value, it should give you the same numbers each time.

float seed = 0.5; // 0.000000000 to 0.999999999 [1]
integer lo = 1; // 0 - 999999 [1]
integer hi = 10; // 0 - 999999 (must be greater than lo) [1]

// [1] these ranges are what were supported in the 'original' code
// I have no idea if LSL can handle them or not.

integer generate()
{
    integer random;
    integer range = hi - lo + 1;
    seed = (seed * 9821) + 0.211327;
    seed = seed - (integer)seed;
    random = (integer)(range * seed) + lo;
    return random;
}

default
{
    touch_start(integer total_number)
    {
        llOwnerSay((string)generate());
    }
}

(assuming it does work) just don't ask me why it works.

I don't get whats random in there?

Well, what happened when you put the script in a cube and kept clicking it?

Bear in mind that the original request was for: "a way to generate the same set of "random" numbers every time based off a given seed value."

You might also try changing the seed value.

This should provide you with a good fast SRNG that won't loop anytime soon and will be impossible to determine the underlying inputs.

integer srng_int = you_decide;
string srng_str = you_decide;
string srng_secret = you_decide;

integer SRNG()
{
    integer i = srng_int & 31;
    integer j = (integer)("0x"+llGetSubString(srng_str = llMD5String(srng_str + srng_secret, srng_int), i - 7, i);
    srng_int = srng_int ^ j;
    return j;
}

The alg is designed so that it can only loop if the inputs of the MD5 function have been seen before or if the MD5 output collides and the i values match. Further crypt analysis needs to be done to ensure the the floating shift does not expose some number of predictable bits in the result.

srng_secret greatly reduces the probability of the MD5 inputs being guessed. It's value does not need to change.

Note that that logic was intented for the hashing of an input string. You'll need something a little more like Strife's algorithm to generate a sequence of seeded pseudo-random values, though I suppose if you passed a value calculated from the above function's output back to the function it could serve.

I created a Mersenne Twister implementation for LSL which gives good random number distribution, only the top 3 functions are required for it to work, you then simply pick which of the helper functions you want/need and copy/paste them into your script as well.

http://wiki.secondlife.com/wiki/Pseudo_Random_Number_Generator