use File::Slurp;

open my $in_file, '<', "file";
binmode($file);

open ( my $out_file, '>', "reversed" ); 
binmode($out_file);

my ( $buf, $data, $n, $bytes ); 

while (( $n = read $in_file, $data, 4096 ) != 0 ) {
	syswrite $out_file, pack( "v*", unpack("n*", $data ));   
	$bytes+=$n;
}

##</code><code>##

use File::Slurp;


open ( my $in_file, '<', "file" );
binmode( $file );

my $temp;
open  my $mem_file, '>', \$temp;
binmode( $mem_file );

my ( $buf, $data, $n, $bytes ); 

while (( $n = read $in_file, $data, 4096 ) != 0 ) {
	syswrite $mem_file, pack( "v*", unpack("n*", $data ));   
	$bytes+=$n;
}

open ( my $out_file, '>', "reversed" ); 
binmode( $out_file );

syswrite ( $out_file, $mem_file );