//----------------------------------------------------------------
//	showjifs.cpp
//
//	This program repeatedly reads and prints the information
//	in our '/proc/jiffies' file for one-million repetitions.
//	In conjunction with the UNIX 'time' command, you can get 
//	a close estimate of the rate at which 'jiffies' is being 
//	incremented, by typing this:
//	
//			      $ time showjifs
//
//	programmer: ALLAN CRUSE
//	written on: 07 SEP 2004
//----------------------------------------------------------------

#include <stdio.h>	// for printf(), perror()
#include <fcntl.h>	// for open()
#include <stdlib.h>	// for exit(), atoi()
#include <unistd.h>	// for read(), close() 
#include <string.h>	// for strtok()

char filename[] = "/proc/jiffies";

int main( void )
{
	int	initial_jiffies = 0;
	int	current_jiffies = 0;
	for (int i = 0; i < 1000000; i++)
		{
		// open the pseudo-file
		int	fd = open( filename, O_RDONLY );
		if ( fd < 0 ) { perror( filename ); exit(1); }
		// read the file's contents
		char	buffer[ 256 ];
		int	nbytes = read( fd, buffer, sizeof( buffer ) );
		if ( nbytes < 0 ) { perror( "read" ); exit(1); }
		// remember the first-time jiffies-value
		current_jiffies = atoi( buffer+8 );
		if ( initial_jiffies == 0 ) 
			initial_jiffies = current_jiffies;
		// replace the final '\n' with a null byte
		strtok( buffer, "\n" );
		// print resulting string on current output-line
		printf( "\r%s ", buffer );
		// close the pseudo-file
		close( fd );
		}
	printf( "\ninitial-value=%d  ", initial_jiffies );
	printf( "final_value=%d  ", current_jiffies );
	printf( "difference=%d \n\n", current_jiffies - initial_jiffies );
}