Seedable PRNG

From Second Life Wiki
Jump to: navigation, search

See also: llFrand, llListRandomize, Pseudo-random_Number_Generator

Note: The 32bit_Hash example presents just the conversion to integer from llMD5String.

md5 based seedable PRNG

It's not the fastest thing but it doesn't seem to have much if any output skew, and I couldn't detect any periodicity in the first 100,000 cycles.

//new md5 based seedable PRNG
//By: Gigs Taggart
//Released under BSD License.
//http://www.opensource.org/licenses/bsd-license.php
 
integer gSeed=0; 
string gLastHash;
 
prng_seed(integer seed)
{
    gSeed=seed;
}
 
integer prng_get()
{
    gLastHash=llMD5String(gLastHash, gSeed); 
    //the bitwise thingy gets rid of negative numbers
    return (integer)("0x" + llGetSubString(gLastHash, 0, 7)) & 0x7FFFFFFF;
}
 
default
{
    state_entry()
    {
        prng_seed(2007031901);
 
        string line;
        integer index;
 
        line = "";
        for (index = 0; index < 9; ++index)
        {
           line += " " + (string) prng_get();
        }
        llOwnerSay(line);
 
        line = "";
        for (index = 0; index < 30; ++index)
        {
           line += " " + (string) (1 + (prng_get() % 6));
        }
        llOwnerSay(line);
 
        llOwnerSay("OK");
    }
}