#!/usr/bin/perl

use warnings;
use strict;

use Sys::Mmap;

use constant SEGMENT_SIZE => 256;
use constant MAX_SEGMENTS => 8192/SEGMENT_SIZE;

my $file = shift;
my $mmap;
if (! -f $file)
{
  die "'$file' is not a regular file\n";
}

open(F, "+< $file")
    or die "Couldn't open '$file': $!\n";

mmap($mmap, 0, PROT_READ|PROT_WRITE, MAP_SHARED, F)
    or die "mmap error: $!\n";

my $segment = 0;
while (<>)
{
  if (length > (SEGMENT_SIZE-1))
  {
    warn "Line too long\n";
    next;
  }
  $segment = ($segment + 1 ) % MAX_SEGMENTS;
  substr($mmap,1+SEGMENT_SIZE*$segment,1)=chr(length);
  substr($mmap,2+SEGMENT_SIZE*$segment,length)=$_;
  substr($mmap,0,1)=chr($segment);
}

##</code><code>##

#!/usr/bin/perl

use warnings;
use strict;

use Sys::Mmap;

use constant SEGMENT_SIZE => 256;
use constant MAX_SEGMENTS => 8192/SEGMENT_SIZE;

my $file = shift;
my $mmap;
if (! -f $file)
{
  die "'$file' is not a regular file\n";
}

open(F, "< $file")
    or die "Couldn't open '$file': $!\n";

mmap($mmap, 0, PROT_READ, MAP_SHARED, F)
    or die "mmap error: $!\n";

my $last_seg = -1;
while (1)
{
  my $segment = ord(substr($mmap,0,1));
  next if ($segment == $last_seg);
  my $len = ord(substr($mmap,1+SEGMENT_SIZE*$segment,1));
  my $line = substr($mmap,2+SEGMENT_SIZE*$segment,$len);
  print $line;
  $last_seg = $segment;
}

##</code><code>##

dd if=/dev/zero bs=1 count=8192 of=mm