#define MEGABYTE		(0x100000L)
#define RECORD_THRESHOLD	(5*1024)

#include <sys/stat.h>
#include <sys/mman.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <limits.h>

int    main()

{
	int fd;
	off_t file_location;
	struct stat file_info;
	char *dummy_ptr;
	char filename[100];

	unsigned char    *block_end_thresh;
	long int	record_threshold;
	long int	file_offset = 0;
	long int	mmapsize = 0;


	fd = open(filename, O_RDONLY );

	if (fd == -1)
	{
	}

	if (-1 == fstat(filename , &file_info))
	{
	}


	/*
	 * Need to make the mmap scroll along with the file.  Use block_end_ptr and
	 * block_end_thresh to do so.
	 */

	record_threshold = sysconf(_SC_PAGE_SIZE);
	file_offset = 0;

	file_location = file_info.st_size;

	if (file_location >= MEGABYTE)
	{
		mmapsize = MEGABYTE;
	}
	else
	{
		mmapsize = env_ptr ->input_file_size;
	}

	block_ptr = mmap(0,mmapsize,PROT_READ,MAP_PRIVATE,env_ptr->input_file,0);

	if (block_ptr == MAP_FAILED)
	{
		/* mmap failed */
	}

	block_end_ptr = block_ptr + mmapsize;
	block_end_thresh = block_ptr + mmapsize - record_threshold;


	dummy_ptr = block_ptr;


	while ((!end_reached) && (dummy_ptr < block_end_ptr))
	{
		if (dummy_ptr > block_end_thresh)
		{
			/* need to slide mmap window */

			int processing_last_block = 0;
			int dummy_offset = dummy_ptr - block_end_thresh;
			
			file_offset += (mmapsize - record_threshold);

			munmap(block_ptr,mmapsize);
			if ((env_ptr ->input_file_size - file_offset) >= MEGABYTE)
			{
				mmapsize = MEGABYTE;
			}
			else
			{
				processing_last_block = 1;
				mmapsize = env_ptr ->input_file_size - file_offset;
			}


			block_ptr = mmap(0,mmapsize,PROT_READ,MAP_PRIVATE,env_ptr->input_file,file_offset);
			if (block_ptr == MAP_FAILED)
			{
				/* ERROR CHECKING */
				return -1;
			}

			block_end_ptr = block_ptr + mmapsize;

			if (processing_last_block)
				block_end_thresh = block_ptr + mmapsize;
			else
				block_end_thresh = block_ptr + mmapsize - record_threshold;

			dummy_ptr = block_ptr + dummy_offset;
		}
		/* your code */

		dummy_ptr++;

	}


	if (block_ptr != NULL)
	{
		munmap(block_ptr,mmapsize);
	}

}