open (FH, "$data_file);
binmode FH;

# set the block size as large practical
# absolutely must be larger than any signature
my $blocksize = 65536;

# get length of largest signature
my $signaturelength = ...;

my $offset = 0;
seek FH, $offset, 0;
while (read FH, $block, $blocksize){

	# check each signature against block
	for $signature (@def_inputs){
		if (# search block for $signature){
			# do signature found stuff
		}
	}

	# seek to next block
	$offset += ($blocksize - $signaturelength);
	seek FH, $offset, 0;
	}
}