Topic: [Removed Bounty] PrimeCoin CUDA miner (Read 8699 times)

This bounty is coming close to being claimed--I can smell it! https://bitcointalksearch.org/topic/xpm-cuda-enabled-qt-client-miner-for-primecoins-source-code-inside-wip-258982

Fixed that for you. FPGA FTW!

Coding directly in low-level CUDA or OpenCL will get the best performance, but perhaps a more quick-and-dirty approach is possible via middleware and code morphing.   

There are a number of CUDA/OpenCL translators and abstraction layers available, allowing development at a higher level.   

Thanks for the BTC!  The explanations on ≡ are correct.  It's just a fancy equals sign for modular arithmetic.

As for the divisibility requirement, it is not just the block depth (not sure if that was what you were asking).  If it were then it would be trivial to start working on the prime chain for the 75,000th block far ahead of time and everyone would be looking for the exact same primes at the same time, meaning the fastest computer would always win.  It is also not just the hex of the block, I don't think, as that would open it up to someone trying to manipulate the block to have the correct hex to allow a precomputed chain of primes to be accepted.  As I understand it you essentially perform a single Bitcoin-style proof of work hash on the block you're looking at and then instead of checking to see if that number is less than a difficulty target as you would do in Bitcoin you search for numbers divisible by it.  I'm not sure the exact order that everything has to go into this hash, but I know that it includes the previous block's hash, the time, the Merkle Root of the transactions, an arbitrary nonce, and likely other data.

Looking at the data associated with a few blocks it would appear that the specific hash that is used is not the current block's "hash" that is used to identify it; I think that hash includes data about the prime chain, which means it can't be used as a requirement for what the primes are.  Looking at block 54321, for example, the prime origin is 4981759032498050152560261402218509159687271713794968969555671831618386493918345 8194973000.  The primorial used here appears to be 2*3*5*7*11*13*17*19*23 (since it is not divisible by the next prime number, 29).  That means the hash was most likely 2233042693160946897388635236176982778377126850264183238825907717991339881869979 00, or 7887e497dbc303fd77e86f8c2ce7c73d96d039643ab695c311987fc2a16f6bfc48 in hex.  If one were to take the (most likely SHA256) hash of parts of the block in a prescribed order then they should get that number.  however, troublingly, that number is 67 hex digits long, which is 268 bits; it appears that I've either made an arithmetic error or that I've misunderstood the procedure. 

As an aside, not the security that this divisibility requirement brings:  the hash value above was approximated by Wolfram Alpha as about 2.2 * the number of atoms in the visible universe.  It is effectively impossible to work on a block out of sequence by guessing a valid origin, as you would be guessing until the heat death of the universe. 

Btw, ill also chip in some btc if we can get this implemented into BFGMiner... https://github.com/luke-jr/bfgminer/tree/prime

The nice thing about using bignums is that you don't have to convert them to decimal - since the internal representation of bignums is in a base of a power of 2 (usually the "digit" size of bignums is 1 or 2 bytes), and the hash is already in that format, we don't have to convert it to decimal. Unless you want a human-readable representation, the number is stored as raw bytes.

e.g. If the prevhash is 0x000...0053, it is internally represented as {0x00, 0x00, ..., 0x53} (or in the opposite order). We can then use this to construct a bignum without converting it into its decimal representation 83.


'≡' means "congruent". In this case it refers to modular congruence - if x ≡ y (mod z), it means that they both have the same remainder mod z. E.g. 3^4 ≡ 1 (mod 5) because 3^4=81 and 1 have the same remainder (1) mod 5.

For now, this thread is only for a CUDA-based miner, however I recommend if you would like to see an OCL one that you put that bounty in its own thread, I might contribute a Bitcoin to that one as well.

I vote for OpenCL, beacause I don't have nor going to buy NVidia, will put another 5BTC to bounty if it's designed for ATI Raedon GPUs.

What currently is the operation that takes up the most time? Is it the testing of primality, or the building of the sieve, or something else altogether?

I think I have a pretty good understanding of the algorithm from a mathematics standpoint.  I don't know CUDA (or OpenCL, which I would suggest--it runs on both NVidia and AMD with reasonably comparable performance) and I don't know the getwork protocol, but I can give some insight into the mathematics, at least.

The first thing to understand is that if the block hash is H then H, 2H, 3H, 4H, etc are all valid origins, and that H-1, 2H-1, 4H-1, 8H-1, etc. makes a valid Cunningham chain (if all of those numbers are prime and the chain is long enough; this is for a Cunningham chain of the first kind.  For the second kind replace the "-" with "+".  Most of the math here will assume Cunningham chains of the First kind, but it is identicle for chains of the Second kind.  If H ± 1, 2H ± 1, ... are all prime (i.e. a chain of the first and second) then the chain is a bi-twin chain).  That means that when you are eliminating composite origins you are also eliminating numbers that could appear later in the chain.  This will become useful later.

Another thing to notice is that H, 2H, 3H, 4H, etc. are very unlikely to be prime.  If you look at the probability that a random number on the order of 2^256 is prime then it is about 1 in 177; that makes the probability that 8 randomly chosen numbers are all primes about 1 in 1 quintillion--impractically low.  That probability is greatly improved by using a "primorial" number--the product of many small primes.  If you take pRimorial= R = H * 2 * 3 * 5 * 7 * .... * 47 (the first 15 prime numbers; quick tests on my own code suggest that this is about ideal, although some tweaking and testing is in order) then you increase the size of the number you are testing, but you also make the numbers much more likely to be prime.  Thus if you look at R-1, 2R -1, etc then you know that each of those numbers is not divisible by 2, 3, 5, ... , 47 because they are 1 less than (or greater than, if you are looking for Cunningham chains of the Second kind) a multiple of each of those numbers.  This means that the smallest factor NR ± 1 can have is 53, where N is any integer.

From here you execute the Sieve.  The standard Sieve of Eratosthenes is very straightforward, but it is designed to be executed starting at 1 and then continuing over the small, consecutive integers, such as is shown on the GIF on the Wikipedia page.  We are not interested in consecutive numbers, and they are far from small, so a change must be adopted.  This change requires knowledge of modular arithmetic.  To execute the sieve we first take a small prime number (starting with 53 if our primorial ended with 47) and take R (mod 53).  If (and only if) R ≡ 0 (mod 53) then R is divisible by 53, and all future R will be divisible by 53.  In that case, no NR-1 will be divisible by 53 and none should be eliminated.

In every other case, R ≡ r (mod 53), where 0 < r < 53.  If you have found that r = 1 then that shows that R-1 ≡ 0 (mod 53) and is therefore not prime (and cannot be a member of a Cunningham Chain of the first kind).  If r = 52 then R+1 ≡ 0 (mod 53) and is therefore not prime.  If r is any other number then you have to search.  Since r is relatively prime to 53 (i.e. gcd(r,53) = 1) it can be shown that N * r (mod 53) will cycle through every number less than 53.  Thanks to modular arithmetic, N * r ≡ N * R (mod 53), so you can search for the N for which N₁ * r ≡ 1 (mod 53) and for which N₂ * r ≡ 52 (mod 53).  You can eliminate N₁R - 1 as a candidate for chains of the first kind, and you can eliminate N₂R + 1 as a candidate for chains of the second kind.

The power of finding this N is that you then know that if N * r ≡ 1 (mod 53) then (53 + N) * r ≡ 1 (mod 53) since N * r is cyclic with a period of 53.  Thus, you can quickly go through, just like in the classic form of the sieve of Eratosthenes, and eliminate every 53rd N.  You would then repeat this process for subsequent prime numbers (59, 61, 67, ...), until sieving against another prime number is not worth it--it takes too long and removes too few numbers.

The next thing you can do to eliminate candidates is to look for clusters (you can actually do this while sieving if you want, but I have separated it since it is a separate topic).  Since the goal is to find chains of (currently) 8 primes it makes no sense to waste time performing a long primality test on a chain of numbers that have passed the sieve that is 7 or fewer long.  Thus, you can look through the sieve for chains in the form N-1, 2N-1, 4N-1, ... 128N-1 where all of those numbers have no small factors (which would have been found in the sieve).  When you find these, they are passed to the formal (probable) primality tests.

The main test used in this step is the Fermat Primality Test, based on Fermat's Little Theorem.  It states that a^P-1 ≡ 1 (mod P) for all prime P.  (It does not state that if that identity holds true then P is prime, but in practice prime numbers are far more likely than "Fermat liars").  For the reference client "a" is chosen to be 2, since 1 is trivially a Fermat Liar for every composite P and since a larger "a" would take more time for no benefit.  To perform the operation it is best to use "fast modular exponentiation," which is shown in pseudocode in the Modular Exponentiation Wikipedia page.

The second test used is the Euler Lagrange Lifchitz test (a brief reading of the code suggests that it is not actually used, but it is implemented.  You can skip this paragraph and not lose much).  It states that if P is prime and P ≡ 1 (mod 4) then 2P + 1 is prime if and only if 2^P + 1 ≡ 0 (mod 2P + 1).  There are other forms as well:  if P ≡ 3 (mod 4) then 2P + 1 is prime if and only if 2^P - 1 ≡ 0 (mod 2P +1).  There are forms for 2P-1 as well; if P ≡ 1 (mod 4) then you use 2^P-1 - 1 ≡ 0 (mod 2P - 1); otherwise it's 2^P-1 + 1 ≡ 0 (mod 2P -1).  These are not much, if any, faster than just using the Fermat primality test--they all rely on a single modular exponentiation, and in all cases the base is 2, and both the exponent and the modulus are on the order of P.  Lifchitz mentions a way to look for Cunningham chains of the second kind "in cluster" by taking 2^n_i-1-1-1 ≡ 0 (mod n * n₁ * n₂ * ... * n_i) where n_i = 2n_i-1-1.  This test only looks for one kind of chain, though, and requires that n ≡ 1 (mod 4).  Also, it is a much more expensive modular exponentiation since the modulus is the product of 8 or more large numbers.

When a prime chain is found that is at least as long as floor(difficulty) (e.g. at least 8 when the difficulty is 8.9) it is necessary to calculate the fractional difficulty.  I haven't verified this in the source code, but in the design paper he takes r = (2^P-1 (mod P) ) as the Fermat remainder, then defines the fractional length as (P - r) / P.  P, in all of this, is the number that would have been next in the chain.  I'm not sure which half of a bi-twin chain has to be used (note that a bi-twin chain can have an odd length if the two Cunningham chains it is made up of differ in length by 1).  If the integer chain length plus the fractional length is greater than the difficulty, it is a valid share.

I hope this has been easy enough to follow, while still being informative.  If anyone has questions I'll try to answer them.  Note that my understanding is based partially on looking at the code but also largely on my own insights; I've likely missed something major, but there is a slim chance that I've offered an improvement on what's already being done simply from coming at it from a different persepctive.  If you feel this satisfies part of your bounty for money, I can receive donations at 1FbWVR3LpGoWp5rc4SJc3cHo42ALrYhcxC.  Not really doing this for the bounty, though.  I just want to be as much help as possible towards making GPU mining a reality, to help neutralize the botnet and massive VPS farm threats. 

Look at CheckPrimeProofOfWork in prime.cpp.

Stellar, sent your 0.25 BTC Cheers!!

the prime chain is linked to the block header hash by requiring that its origin be divisible by the block header hash.
p_k/r is used to measure the difficulty of the chain. r is the Fermat test remainder of the next number in chain p_k
d = k + (p_k- r)/p_k  

k is the prime chain length. d = difficulty if p_k passes probable primality tests then it should be considered as a chain of higher integral length.

my BTC addy is 13YGmE2CCAxWpAhqQSm5NVz9pU7Q4B22jm
thanks

Looks like you know what's up, so I'm gonna grill you for some more information, and if you can provide it you'll be the new owner of a shiny Bitcoin.

2.) I thought that the block hash was used as some factor of either start of chain +1 or start of chain -1 (or in a bi-twin chain, the average between the two first values?). Was this something else that served the purpose of not allowing the same prime chain to be used multiple times?

3.) "getblocktemplate" provides this, which parts are relevant, and how are they relevant, to mining?
{
    "version" : 2,
    "previousblockhash" : "7072f0272b3e38536e072c94e340b7c7824a71989f6e9f3112ce30d6be5ae525",
    "transactions" : [
    ],
    "coinbaseaux" : {
        "flags" : "062f503253482f"
    },
    "coinbasevalue" : 1249000000,
    "target" : "0000000000000000000000000000000000000000000000007118620000000000",
    "mintime" : 1374023934,
    "mutable" : [
        "time",
        "transactions",
        "prevblock"
    ],
    "noncerange" : "00000000ffffffff",
    "sigoplimit" : 20000,
    "sizelimit" : 1000000,
    "curtime" : 1374024884,
    "bits" : "08f11862",
    "height" : 55422
}

Mainly because from what I understand CUDA is more fit to this purpose, as well as it serving as a nice way to get the NVidia players into cryptos as well.

Could you explain this a little bit deeper?
So the sieve produces the set P:={p prime | p <= sieve size} and i have the block hash h. Now i need to find an integer k such that h*k is the origin of a chain of length difficulty. So how is P explicitly used to find a candidate for such an integer k?

This is really interesting! Mathematically, how does the sieve table work? Is one of the primes multiplied by a certain value and then changed in order to obtain a true prime? Also, what address do you want your 0.25 BTC to?

1) I think you got the purpose of the sieve.

2) None.

3) primecoind getblocktemplate

4) primecoind submitblock

From what I understand, CUDA is more apt to this type of work. As well, I think variety is a cool thing, and getting both groups of major video card fanboys in on cryptocoins couldn't hurt.

While I would love OCL (I have 10 7950s and 3 7970s), I think NVidia would be a nice change.