I'm trying to create a game, which I want to always run the same given the same seed. That means that random events - be them what they may - will always be the same for two players using the same seed.
However, given the user's ability to save and load the game, Ruby's Random would reset every time the save loaded, making the whole principle void if two players save and load at different points.
The only solution I have imagined for this is, whenever a save file is loaded, to generate the same number of points as before, and thus getting Ruby's Random to the same state as it was before load. However, to do that I'd need to extend it so a counter is updated every time a random number is generated.
Does anyone know how to do that or has a better way to restore the state of Ruby's Random?
PS: I cannot use an instance of Random (Random.new) and Marshall it. I have to use Ruby's default.
Sounds like Marshal.dump/Marshal.load may be exactly what you want. The Random class documentation explicitly states "Random objects can be marshaled, allowing sequences to be saved and resumed."
You may still have problems with synchronization across games, since different user-based decisions can take you through different logic paths and thus use the sequence of random numbers in entirely different ways.
I'd suggest maybe saving the 'current' data to a file when the user decides to save (or when the program closes) depending on what you prefer.
This can be done using the File class in ruby.
This would mean you'd need to keep track of turns and pass that along with the save data. Or you could loop through the data in the file and find out how many turns have occurred that way I suppose.
So you'd have something like:
def loadGame(loadFile)
loadFile.open
data = loadFile.read
# What you do below here depends on how you decide to store the data in saveGame.
end
def saveGame(saveFile)
saveFile.open
saveFile.puts data
end
Havent really tried the above code so it could be bad syntax or such. It's mainly just the concept I'm trying to get across.
Hopefully that helps?
There are many generators that compute each random number in the sequence from the previous value alone, so if you used one of those you need only save the last random number as part of the state of the game. An example is a basic linear congruential generator, which has the form:
z(n+1) = (az(n) + b) mod c
where a, b and c are typically large (known) constants, and z(0) is the seed.
An arguably better one is the so-called "mulitply-with-carry" method.
Related
A few months back I was tasked with implementing a unique and random code for our web application. The code would have to be user friendly and as small as possible, but still be essentially random (so users couldn't easily predict the next code in the sequence).
It ended up generating values that looked something like this:
Af3nT5Xf2
Unfortunately, I was never satisfied with the implementation. Guid's were out of the question, they were simply too big and difficult for users to type in. I was hoping for something more along the lines of 4 or 5 characters/digits, but our particular implementation would generate noticeably patterned sequences if we encoded to less than 9 characters.
Here's what we ended up doing:
We pulled a unique sequential 32bit id from the database. We then inserted it into the center bits of a 64bit RANDOM integer. We created a lookup table of easily typed and recognized characters (A-Z, a-z, 2-9 skipping easily confused characters such as L,l,1,O,0, etc.). Finally, we used that lookup table to base-54 encode the 64-bit integer. The high bits were random, the low bits were random, but the center bits were sequential.
The final result was a code that was much smaller than a guid and looked random, even though it absolutely wasn't.
I was never satisfied with this particular implementation. What would you guys have done?
Here's how I would do it.
I'd obtain a list of common English words with usage frequency and some grammatical information (like is it a noun or a verb?). I think you can look around the intertubes for some copy. Firefox is open-source and it has a spellchecker... so it must be obtainable somehow.
Then I'd run a filter on it so obscure words are removed and that words which are too long are excluded.
Then my generation algorithm would pick 2 words from the list and concatenate them and add a random 3 digits number.
I can also randomize word selection pattern between verb/nouns like
eatCake778
pickBasket524
rideFlyer113
etc..
the case needn't be camel casing, you can randomize that as well. You can also randomize the placement of the number and the verb/noun.
And since that's a lot of randomizing, Jeff's The Danger of Naïveté is a must-read. Also make sure to study dictionary attacks well in advance.
And after I'd implemented it, I'd run a test to make sure that my algorithms should never collide. If the collision rate was high, then I'd play with the parameters (amount of nouns used, amount of verbs used, length of random number, total number of words, different kinds of casings etc.)
In .NET you can use the RNGCryptoServiceProvider method GetBytes() which will "fill an array of bytes with a cryptographically strong sequence of random values" (from ms documentation).
byte[] randomBytes = new byte[4];
RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider();
rng.GetBytes(randomBytes);
You can increase the lengh of the byte array and pluck out the character values you want to allow.
In C#, I have used the 'System.IO.Path.GetRandomFileName() : String' method... but I was generating salt for debug file names. This method returns stuff that looks like your first example, except with a random '.xyz' file extension too.
If you're in .NET and just want a simpler (but not 'nicer' looking) solution, I would say this is it... you could remove the random file extension if you like.
At the time of this writing, this question's title is:
How can I generate a unique, small, random, and user-friendly key?
To that, I should note that it's not possible in general to create a random value that's also unique, at least if each random value is generated independently of any other. In addition, there are many things you should ask yourself if you want to generate unique identifiers (which come from my section on unique random identifiers):
Can the application easily check identifiers for uniqueness within the desired scope and range (e.g., check whether a file or database record with that identifier already exists)?
Can the application tolerate the risk of generating the same identifier for different resources?
Do identifiers have to be hard to guess, be simply "random-looking", or be neither?
Do identifiers have to be typed in or otherwise relayed by end users?
Is the resource an identifier identifies available to anyone who knows that identifier (even without being logged in or authorized in some way)?
Do identifiers have to be memorable?
In your case, you have several conflicting goals: You want identifiers that are—
unique,
easy to type by end users (including small), and
hard to guess (including random).
Important points you don't mention in the question include:
How will the key be used?
Are other users allowed to access the resource identified by the key, whenever they know the key? If not, then additional access control or a longer key length will be necessary.
Can your application tolerate the risk of duplicate keys? If so, then the keys can be completely randomly generated (such as by a cryptographic RNG). If not, then your goal will be harder to achieve, especially for keys intended for security purposes.
Note that I don't go into the issue of formatting a unique value into a "user-friendly key". There are many ways to do so, and they all come down to mapping unique values one-to-one with "user-friendly keys" — if the input value was unique, the "user-friendly key" will likewise be unique.
If by user friendly, you mean that a user could type the answer in then I think you would want to look in a different direction. I've seen and done implementations for initial random passwords that pick random words and numbers as an easier and less error prone string.
If though you're looking for a way to encode a random code in the URL string which is an issue I've dealt with for awhile then I what I have done is use 64-bit encoded GUIDs.
You could load your list of words as chakrit suggested into a data table or xml file with a unique sequential key. When getting your random word, use a random number generator to determine what words to fetch by their key. If you concatenate 2 of them, I don't think you need to include the numbers in the string unless "true randomness" is part of the goal.
I know that the "how to generate random number" in solidity is a very common question. However, after reading the great majority of answers I did not find one to fit my case.
A short description of what I want to do is: I have a list of objects that each have a unique id, a number. I need to produce a list that contains 25% of those objects, randomly selected each time the function is called. The person calling the function cannot be depended on to provide input that will somehow influence predictably the resulting list.
The only answer I found that gives a secure random number was Here. However, it depends on input coming from the participants and it is meant to address a gambling scenario. I cannot use it in my implementation.
All other cases mention that the number generated is going to be predictable, and even some of those depend on a singular input to produce a single random number. Once again, does not help me.
Summarising, I need a function that will give me multiple, non-predictable, random numbers.
Thanks for any help.
Here is an option:
function rand()
public
view
returns(uint256)
{
uint256 seed = uint256(keccak256(abi.encodePacked(
block.timestamp + block.difficulty +
((uint256(keccak256(abi.encodePacked(block.coinbase)))) / (now)) +
block.gaslimit +
((uint256(keccak256(abi.encodePacked(msg.sender)))) / (now)) +
block.number
)));
return (seed - ((seed / 1000) * 1000));
}
It generates a random number between 0-999, and basically it's impossible to predict it (It has been used by some famous Dapps like Fomo3D).
Smart Contracts are deterministic, so, basically every functions are predictable - if we know input, we will be and we should be know output. And you cannot get random number without any input - almost every language generates "pseudo random number" using clock. This means, you will not get random number in blockchain using simple method.
There are many interesting methods to generate random number using Smart Contract - using DAO, Oracle, etc. - but they all have some trade-offs.
So in conclusion, There is no method you are looking for. You need to sacrifice something.
:(
100% randomness is definitely impossible on Ethereum. The reason for that is that when distributed nodes are building from the scratch the blockchain they will build the state by running every single transaction ever created on the blockchain, and all of them have to achieve the exact same final status. In order to do that randomness is totally forbidden from the Ethereum Virtual Machine, since otherwise each execution of the exact same code would potentially yield a different result, which would make impossible to reach a common final status among all participants of the network.
That being said, there are projects like RanDAO that pretend to create trustable pseudorandomness on the blockchain.
In any case, there are approaches to achieve pseudandomness, being two of the most important ones commit-reveal techniques and using an oracle (or a combination of both).
As an example that just occurred to me: you could use Oraclize to call from time to time to a trusted external JSON API that returns pseudorandom numbers and verify on the contract that the call has truly been performed.
Of course the downside of these methods is that you and/or your users will have to spend more gas executing the smart contracts, but it's in my opinion a fair price for the huge benefits in security.
I'm creating a game where I want to create random worlds and give the player the option of having the same world made again by entering the same seed...
So... How can I do this? It will generate the same set of numbers, but not the same every time you call for the random function...
Do I have to make function of sorts based on the seed manually?
In GameMaker Studio and GameMaker 8.1 there is a function:
random_set_seed(seed)
Here you can enter your seed.
Then random(x) gives the same n-th result per game run.
random(100)
randomize() // This doesn't change rand[0] or rand[1]
random_set_seed(20) // because of this
rand[0]=random(100)
rand[1]=random(100)
Randomizer functions either use mathematical formulas which seem to give out random numbers or just look at an already calculated array of seemingly random numbers and return them in order. In most languages, there is a function which will look at the computer's clock and will use this value as a first value for the mathematical formula or as a starting index in the pseudorandom array. In GameMaker, you can use randomize() to do that. Only call that once when the game launches and you'll get different results on every execution.
If you want the opposite, that is you want to be able to regenerate the same seemingly random sequence, you can instead set the seed manually with random_set_seed(value). The value passed needs to be a number. Then you can give that seed to the player.
So if you want to generate a random level on the first time and later be able to replay the same level, you need to do in order:
Call randomize to set a random seed.
Call random_get_seed which will return the current seed.
Call random and the likes to generate a level.
When the player wants to use the same seed as before, call random_set_seed and pass it the seed.
Warning: By using those functions, you are putting your trust in GM's randomizing functions. These are platform dependent, and the functions might change in a later version of GM. If you want your seeds to work across all platforms and versions of your game, you might want to work on your own randomizing functions.
I hope it's not too obvious a question: is there a random number generation algorithm that doesn't depend on previously returned values, so that I can get (for example) the 50th number in the sequence, without computing the previous 49?
The reason is that I am making roguelike that will be persistent (so that I can recreate the exact same level from the same seed), but to compute certain features of each level, I don't want to have to "compute" all previous features just to get the random number generator to the correct "state" of having been used, for example, 100 times so far. I would like to be able to query the 101st random number without determining previous values so that the program can create level features separately.
You can encrypt ordinary sequence number [1..N] with any cipher,
and by this way - generate unique pseudorandom value for each SeqNo.
If you use a linear congruential random number generator, it is trivial to compute the $n$-th element generated from a given seed. But it is probably easier just to stash away the state at the "interesting" points of the game.
OTOH, if you want to "restart" the game at a certain point, you'll presumably want to be able to recreate the dungeon's features, but (due to different player actions) the RNG usage will be different from then on. I.e., if started at the same point, if I shoot twice at a monster the RNG will be used more times than if I just run away; the next item generated will get different values. Perhaps what you really want is several independent random number streams, and saving the states as needed?
There are lots of roguelike games around, mostly open source. Some are limited/small (from "build a game in a day" sort of competitions), and might make a good starting point for you. Why start your own, and not hack on an existing one?
I'm writing a web app similar to wtfimages.com in that one visitor should never (or rarely) see the same thing twice, but different visitors can see the same thing. Ideally, this would span visits, so that when Bob comes back tomorrow he doesn't see today's things again either.
Three first guesses:
have enough unique things that it's unlikely any user will draw enough items to repeat
actually track each user somehow and log what he has seen
have client-side Javascript request things by id according to a pseudorandom sequence seeded with something unique to the visitor and session (e.g., IP and time)
Edit: So the question is, which of these three is the best solution? Is there a better one?
Note: I suspect this question is the web 2.0 equivalent of "how do I implement strcpy?", where everybody worth his salt knows K&R's idiomatic while(*s++ = *t++) ; solution. If that's the case, please point me to the web 2.0 K&R, because this specific question is immaterial. I just wanted a a "join the 21st century" project to learn CGI scripting with Python and AJAX with jQuery.
The simplest implementation I can think of would be to make a circular linked list, and then start individual users at random offsets in the linked list. You are guaranteed that they will see every image there is to see before they will see any image twice.
Technically, it only needs to be a linked list in a conceptual sense. For example, you could just use the database identifiers of the various items and wrap around once you've hit the last one.
There are complexity problems with other solutions. For example, if you want it to be a different order for each person, that requires permuting the elements in some way. But then you have to store that permutation, so as to guarantee that people see things in different orders. That's going to take up a lot of space. It will also require you to update everybody's permutations if you add or remove an image to the list of things to see, which is yet more work.
A compromise solution that still allows you to guarantee a person sees every image before they see any image twice while still varying things among people might be something like this:
Using some hash function H (say, MD5), take the hash of each image, and store the image with a filename equal to the digest (e.g. 194db8c5[...].jpg).
Decide on a number N. This will be the number of different paths that a randomly selected person could take to traverse all the images. For example, if you pick N = 10, each person will take one of 10 possible distinct journeys through the images. Don't pick an N larger than the digest size of H (for MD5, this is 16; for SHA-1, it's 64).
Make N different permutations of the image list, with the ith such permutation being generated by rotating the characters in each file name i characters to the left, and then sorting all the entries. (For example, a file originally named abcdef with i == 4 will become efabcd. Now sort all the files that have been transformed in this way, and you have a distinct list.)
Randomly assign to each user a number r from 0 .. N - 1 inclusive. They now see the images in the ordering specified by r.
Ultimately, this seems like a lot of work. I'd say just suck it up and make it random, accept that people will occasionally see the same image again, and move on.
Personally I would just store a cookie on the user's machine which holds all the ID's of what he's seen. That way you can keep the 'randomness' and not have to show the items in sequential order as John Feminella's otherwise great solution suggests.
Applying the cookie data in an SQL query would also be trivial: say that you have a comma separated ID's in the cookie, you can just do this (in PHP):
"SELECT image FROM images WHERE id NOT IN(".$_COOKIE['myData'].") ORDER BY RAND() LIMIT 1"
Note that this is just an simple example, you should of course escape the cookie data properly and there might be more efficient ways to select a random entry from a table.
Using a cookie also makes it possible to start off where the user left off the previous time. And cookie sizes won't probably be an issue, you can hold a lot of ID's in 4KB which is (usually) the maximum size of cookie files.
EDIT
If your cookie data looks like this:
$_COOKIE['myData'] == '1,6,19,200,70,16';
You can safely use that data in a SQL query with:
$ids = array_map('mysql_real_escape_string', explode(',', $_COOKIE['myData']));
$query = "SELECT image FROM images WHERE id NOT IN('".implode("', '", $ids)."') ORDER BY RAND() LIMIT 1"
What this will do is that it splits the ID string into individual ID's, then runs mysql_real_escape_string to each of them, then implodes them with quotes so that the query becomes:
$query == "SELECT image FROM images WHERE id NOT IN('1', '6', '19', '200', '70', '16') ORDER BY RAND() LIMIT 1"
So $_COOKIE[] variables are just like any other variable, and you must do same precautions for them as with other data.
You have 2 class of solutions:
state-less
state-full
You need to pick one: (#1) is of course not guaranteed (i.e. probability of showing same image to user is variable) whilst (#2) allows you guarantees (depending on the implementation of course).
Here is another suggestion you might want to consider:
Maintain state on the Client-Side through HTML5 localstorage (when available): the value of this option will only continue to increase as Web Browsers with HTML5 support increases.