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C++ Program to find prime numbers [ FINISHED ! ]
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tombana
Master Cheater

Reputation: 2

Joined: 14 Jun 2007
Posts: 456
Location: The Netherlands

Posted: Fri Dec 17, 2010 12:39 pm Post subject:

Flyte wrote:

Bitches don't know 'bout template meta-programming.

Constant time, yo.

wow

HomerSexual
Grandmaster Cheater Supreme

Reputation: 5

Joined: 03 Feb 2007
Posts: 1657

Posted: Sat Dec 18, 2010 10:58 am Post subject:

Wiccaan wrote:

HomerSexual wrote:

Code:

// Initialize pos 0, 1 to false.
primeCache.set( 0, false );
primeCache.set( 1, false );

I'm confused by these lines

Not sure if you are confused by the code itself or my wording of it. By saying pos 0, 1 I didn't mean like a graph or anything, meant 0 and 1 are both not prime so their positions inside the bit array are set to false manually.

Not setting 0 manually will cause the first loops test to succeed when x = 0, turning the second loop into an infinite loop due to the stepping.
y += x will never properly step if x is 0 so it will never continue.

Not setting 1 manually will cause the full array to set to false. Instead of stepping the proper x * x + y which should multiply forward it steps every number because x = 1, so you land up with y = x * x, y += x, 1 * 1 + 1 = 2, 2 + 1 = 3, 3 + 1 etc. so it will end up stepping every number in the bitset.

(This is not including the theory that 0 is/isn't prime and/or is/isn't a number and all that fun jazz.)

oh my bad totally misread the code, my apologies. That's embarrassing >.<
_________________

sangeli
Master Cheater

Reputation: 0

Joined: 07 Dec 2006
Posts: 406

Posted: Sat Dec 18, 2010 4:17 pm Post subject:

Slugsnack wrote:

educofu wrote:

sangeli wrote:

I didn't read into the other posts very much but remember that you only need to count up to the square root of the number to look for multiples. should save time.

didnt work. but counting up to the half of the number does.

You don't need to count up to half. Counting up to the ceiling of the square root will do.

mhmm
_________________

Dark Byte wrote:

ce can certainly damage hardware let's say you have a robotarm attached to your computer, and the software limits usually block it from ripping out it's own cpu. If you remove that limit and then issue the command to rip out the cpu, sure, say goodbye to your hardware

Jorg hi
I post too much

Reputation: 7

Joined: 24 Dec 2007
Posts: 2276
Location: Minnesota

Posted: Sat Dec 18, 2010 4:40 pm Post subject:

0 isn't a prime number xD it can be divided by 0. Zero should be a special prime number in my opinion. _________________ CEF will always stay alive.

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