## GetPrimes(topInt)

##### Last updated July 31, 2004

**Version:** 3 |
**Requires:** CF5 |
**Library:** MathLib

**Description:**

Creates an array of all the prime numbers from 1 to the specified integer.

**Return Values:**

Returns an array.

**Example:**

`<cfdump var="#getprimes(1000)#">`

**Parameters:**

Name | Description | Required |
---|---|---|

topInt | The number to calculate primes for. | Yes |

**Full UDF Source: **

```
/**
* Creates an array of all the prime numbers from 1 to the specified integer.
*
* @param topInt The number to calculate primes for. (Required)
* @return Returns an array.
* @author Steven Van Gemert (svg2@placs.net)
* @version 3, July 31, 2004
*/
function GetPrimes(topInt) {
var stepInt = 0;
var i = 0;
var primes = arraynew(1);
var di = 4; //Wheel factor.
var maxfactor = 0;
var thisnumberoffactors = 0;
var thismaxfactor = 0;
var isprime = "yes";
if(topInt is 1) return primes;
primes[1] = 2;
if(topInt is 2) return primes;
primes[2] = 3;
if(topInt LTE 4) return primes;
maxfactor = ceiling(sqr(topInt));
primes = getPrimes(maxfactor); //Recursion call. Find the primes for the square root of the passed number.
//Make the current maxfactor odd. We will use this as a starting point for checking for primes above the square root of this number.
maxfactor = maxfactor + 1 + (1 * (not ((maxfactor + 1) mod 2)));
//Now determine the appropriate wheel factor beginning value.
if(not (maxfactor mod 3)){
maxfactor = maxfactor + 2;
di = 4;
} else if(not ((maxfactor + 2) mod 3)){
di = 2;
}
else{
di = 4;
}
thisnumberoffactors = arraylen(primes);
for(stepInt=maxfactor; stepInt lte topInt; stepInt=stepInt+di) {
di = 6 - di; //Implement wheel factor. Every third odd number will be divisible by 3. Don't check it.
//This will be the limit to where we check for factors. There must be at least one factor less than the square root of the number.
thismaxfactor = sqr(stepInt);
isprime = "yes"; //Assume this number is prime.
for(i=1; i LTE thisnumberoffactors; i = i + 1){ //For each factor...
if(not (stepInt mod primes[i])){
isprime = "no"; //Indicate that this number is not prime.
break; //Break if we find a valid factor.
} else if(primes[i] GT thismaxfactor){ //If we have reached the square root.
break; //Stop processing...we have now validated this number as a prime.
}
}
if(isprime)ArrayAppend(primes,stepInt); //If this number is prime, then add it to the array of primes.
}
return primes;
}
```

blog comments powered by Disqus
### Search CFLib.org

### Latest Additions

Kevin Cotton added

date2ExcelDate

May 5, 2016

Raymond Camden added

CapFirst

April 25, 2016

Chris Wigginton added

loremIpsum

January 18, 2016

Gary Stanton added

calculateArrival...

November 19, 2015

Sebastiaan Naafs - van Dijk added

getDaysInQuarter

November 13, 2015