Prime Numbers, Modulus Operator Help

Quote:

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Originally Posted by abachler

As for padding, personally I use a much faster although more convoluted method of updating Root that bypasses the slow SQRT() function. Since im assuming the teacher will not enter some obtusely large number for the count of primes to find ( like 200 million) runtime shouldnt be an issue.

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You don't need to use sqrt() to do the optimization.

Code:

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result = possible_prime / possible_factor;
if(result < possible_factor)
{
    /* Obviously, we've crossed the square root at this point. */
}

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HEY you've been looking at my notes :D

Actually I just do that step to determine if I need to Root++

Code:

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if(Prime / Root > Root) Root+=2;

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different implementation, btu the same core method. The reason I increase root by 2 is we will only be checking odd number factors anyway.

Quote:

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Originally Posted by vart

too optimized

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then try this -

Code:

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if(!(Prime & 1)) return FALSE;

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Quote:

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Originally Posted by abachler

then try this -

Code:

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if(!(Prime & 1)) return FALSE;

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it was a joke, checking Prime in any way will do you no good here... As was said - you need to test the value of Target

oh gawd, yeah i totally missed that one, it shodul be

Code:

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if(!(Target & 1)) return FALSE;

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thanks for catching that nub mistake vart :D

BTW, for anyone that tried to D/L the primes in the last few days and got a service message, the site is back up and running. Sorry I forgot to pay the bill :rolleyes: