SSTF_disk_scheduling.c

// C  program for implementation of
// SSTF (shortest seek time first disk scheduling
// algoritm. Time complexity= O(n^2)
#include <stdio.h>
#include <stdlib.h>
#include <string.h>


// Calculates difference of each
// track number with the head position
void calculatedifference(int request[], int head,
						int diff[][2], int n)
{
	for(int i = 0; i < n; i++)
	{
		diff[i][0] = abs(head - request[i]);
	}
}

// Find unaccessed track which is
// at minimum distance from head
int findMIN(int diff[][2], int n)
{
	int index = -1;
	int minimum = 1e9;

	for(int i = 0; i < n; i++)
	{
		if (!diff[i][1] && minimum > diff[i][0])
		{
			minimum = diff[i][0];
			index = i;
		}
	}
	return index;
}

void shortestSeekTimeFirst(int request[],
						int head, int n)
{
	if (n == 0)
	{
		return;
	}
	
	// Create array of objects of class node
	int diff[n][2];
	memset(diff,0,n*2*sizeof(int));
	
	// Count total number of seek operation
	int seekcount = 0;
	
	// Stores sequence in which disk access is done
	int seeksequence[n + 1];
	memset(seeksequence,0,(n+1)*sizeof(int));
	
	for(int i = 0; i < n; i++)
	{
		seeksequence[i] = head;
		calculatedifference(request, head, diff, n);
		int index = findMIN(diff, n);
		diff[index][1] = 1;
		
		// Increase the total count
		seekcount += diff[index][0];
		
		// Accessed track is now new head
		head = request[index];
	}
	seeksequence[n] = head;
	
	printf("Total number of seek operations = %i\n",seekcount);
	printf("Seek sequence is : ""\n");
	
	// Print the sequence
	for(int i = 0; i <= n; i++)
	{
	  printf("%i",seeksequence[i]);
	  printf("\n");
	}
}

// Driver code
int main()
{
	int n = 8;
	int proc[8] = { 176, 79, 34, 60, 92, 11, 41, 114 };
	
	shortestSeekTimeFirst(proc, 50, n);
	
	return 0;
}