Write a program that implements the SSTF, C-SCAN and LOOK disk-scheduling algori
ID: 3765091 • Letter: W
Question
Write a program that implements the SSTF, C-SCAN and LOOK disk-scheduling algorithms presented in Chapter 10 of the textbook. Your program will service a disk with 5,000 cylinders numbered 0 to 4,999. It will have a specific list of cylinder requests (you must use the one provided in the skeletal code file, but you can also try different ones of your own). The program has to be passed the initial position of the disk head. The implemented functions need to compute the number of head movements for each algorithm as explained in detail below
Explanation / Answer
#include <iostream>
#include <cstdlib>
#include <conio.h>
#include <math.h>
using namespace std;
int compare (const void * a, const void * b)
{
if ( *(int*)a < *(int*)b ) return -1;
if ( *(int*)a == *(int*)b ) return 0;
if ( *(int*)a > *(int*)b ) return 1;
}
void shift(int a[],const int size)
{
for(int i=1;i<=size;i++)
a[i-1]=a[i];
}
class disk
{
private :
int request[101];
int sorted_request[101];
int number_of_request;
int max;
int direction;
public :
disk()
{
cout<<" Enter maximum disk limit : ";
cin>>max;
}
void receive_request()
{
enter_request_number:
cout<<" Enter number of requests (max. 100): ";
cin>>number_of_request;
if(number_of_request>100)
goto enter_request_number;
current_location:
cout<<" Enter current location : ";
cin>>request[0];
sorted_request[0]=request[0];
if(request[0]>max||request[0]<0)
goto current_location;
current_direction:
cout<<" Enter current direction(0:left / 1:right) : ";
cin>>direction;
if(direction!=0&&direction!=1)
goto current_direction;
for(int i=1;i<=number_of_request;i++)
{
cout<<" Enter request number "<<i<<" : ";
cin>>request[i];
sorted_request[i]=request[i];
if(request[i]>max||request[i]<0)
{
cout<<" Invalid request !! Enter again!!";
i--;
}
}
qsort(sorted_request+1,number_of_request,sizeof(int),compare);
}
int fcfs()
{
int head_movement=0;
for(int i=1;i<=number_of_request;i++)
head_movement+=abs(request[i]-request[i-1]);
return head_movement;
}
int sstf()
{
int head_movement=0,flag=0,nor=number_of_request;
int request[101];
request[0]=sorted_request[0];
for(int i=1;i<=number_of_request;i++)
{
if(sorted_request[i]>sorted_request[0]&&flag==0)
flag=i;
request[i]=sorted_request[i];
}
while(nor)
{
if(flag==0)
{
head_movement+=request[0]-request[nor];
request[0]=request[nor];
}
else if(flag==1)
{
head_movement+=abs(request[nor]-request[0]);
break;
}
else if((request[flag]-request[0])>(request[0]-request[flag-1]))
{
head_movement+=request[0]-request[flag-1];
request[0]=request[flag-1];
flag--;
shift(request+flag,nor-flag);
}
else
{
head_movement+=request[flag]-request[0];
request[0]=request[flag];
shift(request+flag,nor-flag);
}
nor--;
}
return head_movement;
}
int SCAN()
{
int head_movement=0,flag=0;
for(int i=1;i<=number_of_request;i++)
if(sorted_request[i]>sorted_request[0]&&flag==0)
flag=i;
if(direction==1)
{
if(flag==1)
head_movement+=sorted_request[number_of_request]-sorted_request[0];
else
{
head_movement+=max-sorted_request[0];
head_movement+=max-sorted_request[1];
}
}
else
{
if(flag==0)
head_movement+=abs(sorted_request[number_of_request]-sorted_request[0]);
else
{
head_movement+=sorted_request[0];
head_movement+=sorted_request[number_of_request];
}
}
return head_movement;
}
int CSCAN()
{
int head_movement=0,flag=0;
for(int i=1;i<=number_of_request;i++)
if(sorted_request[i]>sorted_request[0]&&flag==0)
flag=i;
if(flag==1)
head_movement+=sorted_request[number_of_request]-sorted_request[0];
else
{
head_movement+=max-sorted_request[0];
head_movement+=max;
head_movement+=max-sorted_request[flag-1];
}
return head_movement;
}
int LOOK()
{
int head_movement=0,flag=0;
for(int i=1;i<=number_of_request;i++)
if(sorted_request[i]>sorted_request[0]&&flag==0)
flag=i;
if(direction==1)
{
if(flag==1)
head_movement+=sorted_request[number_of_request]-sorted_request[0];
else
{
head_movement+=sorted_request[number_of_request]-sorted_request[0];
head_movement+=sorted_request[number_of_request]-sorted_request[1];
}
}
else
{
if(flag==0)
head_movement+=abs(sorted_request[number_of_request]-sorted_request[0]);
else
{
head_movement+=sorted_request[1];
head_movement+=sorted_request[number_of_request]-sorted_request[1];
}
}
return head_movement;
}
int CLOOK()
{
int head_movement=0,flag=0;
for(int i=1;i<=number_of_request;i++)
if(sorted_request[i]>sorted_request[0]&&flag==0)
flag=i;
if(flag==1)
head_movement+=sorted_request[number_of_request]-sorted_request[0];
else
{
head_movement+=sorted_request[number_of_request]-sorted_request[0];
head_movement+=sorted_request[number_of_request]-sorted_request[1];
head_movement+=sorted_request[flag-1]-sorted_request[1];
}
return head_movement;
}
~disk(){}
};
int main()
{
disk hdd;
hdd.receive_request();
cout<<"Total head movement in ";
cout<<"FCFS is "<<hdd.fcfs()<<endl;
cout<<"Total head movement in ";
cout<<"SSTF is "<<hdd.sstf()<<endl;
cout<<"Total head movement in ";
cout<<"SCAN is "<<hdd.SCAN()<<endl;
cout<<"Total head movement in ";
cout<<"CSCAN is "<<hdd.CSCAN()<<endl;
cout<<"Total head movement in ";
cout<<"LOOK is "<<hdd.LOOK()<<endl;
cout<<"Total head movement in ";
cout<<"CLOOK is "<<hdd.CLOOK()<<endl;
getch();
}
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