isPrime, optimization 2

Only divide by odd numbers, until the square root of the number.

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bool isPrime2( int x ) { if( x == 2 ) { return true; } if( x % 2 == 0 ) { return false; } int limit = (int) sqrt(x); for( int divisor = 3; divisor <= limit; divisor += 2 ) { if( x % divisor == 0 ) { return false; } } return true; }

Other entries:

• isPrime: Naive version 
• isPrime, Optimization 1: Iterate only until the square root of the number
• isPrime, Optimization 2: Only divide by odd numbers, until the square root of the number
• isPrime, Optimization 3: Skip the divisors that are multiple of 2 or 3
• Keep the previosly generated primes and use them to test the following numbers.
• isPrime, Recursive.