Merge e156b8afd5 into 2c67b48c21

I improved the performances of trialDivision by performing fewer checks, while still using the same overall idea of the algorithm.

src/algorithms/math/primality-test/trialDivision.js

@@ -8,25 +8,19 @@ export default function trialDivision(number) {
     return false;
   }
 
-  if (number <= 1) {
-    // If number is less than one then it isn't prime by definition.
-    return false;
-  }
-
   if (number <= 3) {
-    // All numbers from 2 to 3 are prime.
-    return true;
+    // If number is less than one then it isn't prime by definition. But all numbers from 2 to 3 are prime.
+    return number > 1;
   }
 
-  // If the number is not divided by 2 then we may eliminate all further even dividers.
-  if (number % 2 === 0) {
+  // If the number is not divided by 2 or 3 then we may eliminate all further even dividers.
+  if (number % 2 === 0 || number % 3 === 0) {
     return false;
   }
 
-  // If there is no dividers up to square root of n then there is no higher dividers as well.
-  const dividerLimit = Math.sqrt(number);
-  for (let divider = 3; divider <= dividerLimit; divider += 2) {
-    if (number % divider === 0) {
+  // If there is no dividers up to square root of divider then there is no higher dividers as well. To make the algorithm more efficient, we increment by 6 everytime, and make sure to check divider + 2 as well.
+  for (let divider = 5; number >= (divider * divider); divider += 6) {
+    if (number % divider === 0 || number % (divider + 2) === 0) {
       return false;
     }
   }