computation speed

[iamcow]

just something i did while fooling around with a piece of code

code:

var primes : array 2 .. 99999999 of boolean proc findprime (num : int)     var counter := 0     var n : real     for decreasing i : num-1 .. 2         n := num / i         if round (n) = n then             counter += 1         else             counter := counter         end if     end for     if counter = 0 then         primes (num) := true     else         primes (num) := false     end if end findprime for i : 2 .. 99999999     findprime (i) end for for i : 2 .. 99999999     if primes (i) = true then         put i, " is a prime"     else         put i, " is not a prime"     end if end for

out of curiousity, how long does it take for you guys to run this program?

[[Gandalf]]

Umm... I'd imagine extremely long, even on an amazing computer. Why do you ask?

And just from a glance, you're findPrime function doesn't look quite right, and neither does your code.

[pj_ladd12]

yeah...nothing came up lol

[BenLi]

changed all "99999999"'s to 100s
the code works actually, i imagine its just quite slow.

Interesting, this is the subject of another discussion in general forum. The one about largest primes?

[[Gandalf]]

pj_ladd12 wrote:

yeah...nothing came up lol

Yeah, that's because it's taking a very long time to calculate what it's going to display.

Quote:

Interesting, this is the subject of another discussion in general forum. The one about largest primes?

I doubt you'd get very far using this algorithm and Turing.

[Clayton]

I'm sure theres a much better way to do this, it just had to be extremely well organized and optimized , the only problem is, Turing can't deal with big enough numbers to find the worlds next largest prime with over 10,000,000 digits

[MysticVegeta]

Why not just try the Sieve of Eratosthenes to find it quicker than that algorithm but still it takes time to find that many...

http://compsci.ca/v2/viewtopic.php?t=11966

[CodeMonkey2000]

var primes : array 2 .. 99999999 of boolean


wow soo much time was spent on just declareing the all elements of primes.
turing really isnt that powerful.

[Andy]

spearmonkey2000 wrote:

var primes : array 2 .. 99999999 of boolean


wow soo much time was spent on just declareing the all elements of primes.
turing really isnt that powerful.

what? you clearly have no knowledge of the computer memory interface. when declaring 99999998 boolean variables, 99999998bytes of contiguous memory (either on RAM, or on disk through an TLB) is allocated, it's all done by the processor, and has nothing to do with turing's efficiency