We have discussed loop unrolling. The idea is to increase performance by grouping loop statements so that there are less number of loop control instruction and loop test instructions
C++
// CPP program to compare normal loops and// loops with unrolling technique#include <iostream>#include <time.h>using namespace std;int main() { // n is 8 lakhs int n = 800000; // t to note start time clock_t t = clock(); // to store the sum long long int sum = 0; // Normal loop for (int i = 1; i <= n; i++) sum += i; // to mark end time t = clock() - t; cout << "sum is: " << sum << endl; cout << "time taken by normal loops:" "(float)t / CLOCKS_PER_SEC << " seconds" << endl; // to mark start time of unrolling t = clock(); // Unrolling technique (assuming that // n is a multiple of 8). sum = 0; for (int i = 1; i <= n; i += 8) { sum += i sum += (i + 1); sum += (i + 2); sum += (i + 3); sum += (i + 4); sum += (i + 5); sum += (i + 6); sum += (i + 7); } // to mark the end of loop t = clock() - t; cout << "Sum is: " << sum << endl; cout << "Time taken by unrolling: " "(float)t / CLOCKS_PER_SEC << " seconds"; return 0;} |
Java
// Java program to compare // normal loops and loops // with unrolling techniqueclass GFG{ public static void main(String[] args) { // n is 8 lakhs int n = 800000; // t to note start time double t = (double)System.nanoTime(); // to store the sum long sum = 0; // Normal loop for (int i = 1; i <= n; i++) sum += i; // to mark end time t = (double)System.nanoTime() - t; System.out.println("sum is: "+ Double.toString(sum)); System.out.println("time taken by normal loops:" + Double.toString(t / Math.pow(10.0, 9.0))); // to mark start time // of unrolling t = (double)System.nanoTime(); // Unrolling technique // (assuming that n is // a multiple of 8). sum = 0; for (int i = 1; i <= n; i += 8) { sum += i ; sum += (i + 1); sum += (i + 2); sum += (i + 3); sum += (i + 4); sum += (i + 5); sum += (i + 6); sum += (i + 7); } // to mark the end of loop t = (double)System.nanoTime() - t; System.out.println("sum is: " + Double.toString(sum)); System.out.println("time taken by normal loops:" + Double.toString(t / Math.pow(10.0, 9.0))); }}// This code is contributed // by Harshit Saini |
Python3
# Python program to compare # normal loops and loops # with unrolling techniquefrom timeit import default_timer as clockif __name__ == "__main__": # n is 8 lakhs n = 800000; #t to note start time t = clock() # to store the sum sum = 0 # Normal loop for i in range(1, n + 1): sum += i # to mark end time t = clock() - t print("sum is: " + str(sum)) print("time taken by normal " + "loops:" + str(t)) # to mark start # time of unrolling t = clock() # Unrolling technique # (assuming that n is # a multiple of 8). sum = 0 for i in range(1, n + 1, 8): sum += i sum += (i + 1) sum += (i + 2) sum += (i + 3) sum += (i + 4) sum += (i + 5) sum += (i + 6) sum += (i + 7) # to mark the # end of loop t = clock() - t print("Sum is: " + str(sum)) print("Time taken by unrolling: " + str(t)) # This code is contributed# by Harshit Saini |
C#
// C# program to compare // normal loops and loops // with unrolling techniqueusing System;using System.Diagnostics; class GFG{ private static double nanoTime() { long nano = 10000L * Stopwatch.GetTimestamp(); nano /= TimeSpan.TicksPerMillisecond; nano *= 100L; return nano; } public static void Main(String[] args) { // n is 8 lakhs int n = 800000; // t to note start time double t = nanoTime(); // to store the sum long sum = 0; // Normal loop for (int i = 1; i <= n; i++) sum += i; // to mark end time t = nanoTime() - t; Console.WriteLine("sum is: "+ sum); Console.WriteLine("time taken by normal loops:" + (t / Math.Pow(10.0, 9.0))); // to mark start time // of unrolling t = nanoTime(); // Unrolling technique // (assuming that n is // a multiple of 8). sum = 0; for (int i = 1; i <= n; i += 8) { sum += i ; sum += (i + 1); sum += (i + 2); sum += (i + 3); sum += (i + 4); sum += (i + 5); sum += (i + 6); sum += (i + 7); } // to mark the end of loop t = nanoTime() - t; Console.WriteLine("sum is: " + (sum)); Console.WriteLine("time taken by normal loops:" + (t / Math.Pow(10.0, 9.0))); }}// This code is contributed by 29AjayKumar |
Javascript
<script>// javascript program to compare // normal loops and loops // with unrolling technique // n is 8 lakhs var n = 800000; // t to note start time var t = new Date(); // to store the sum var sum = 0; // Normal loop for (let i = 1; i <= n; i++) sum += i; // to mark end time t = new Date() - t; document.write("sum is: " +(sum)); document.write("<br/>time taken by normal loops:" + (t / Math.pow(10.0, 9.0)).toFixed(10)); // to mark start time // of unrolling t = new Date(); // Unrolling technique // (assuming that n is // a multiple of 8). sum = 0; for (i = 1; i <= n; i += 8) { sum += i; sum += (i + 1); sum += (i + 2); sum += (i + 3); sum += (i + 4); sum += (i + 5); sum += (i + 6); sum += (i + 7); } // to mark the end of loop t = new Date() - t; document.write("<br/>sum is: " + (sum)); document.write("<br/>time taken by normal loops:" + (t / Math.pow(10.0, 9.0)).toFixed(10));// This code is contributed by Rajput-Ji</script> |
Output:
Sum is: 320000400000 Time taken: 0.002645 seconds Sum is: 320000400000 Time taken: 0.001799 seconds
Please refer loop unrolling for comparison of normal loops and loop unrolling.
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