I was confused by your textual description of the binary format as well as your code.

In general when processing binary files, avoid regex. Your friends should be: substr,ord,unpack and pack.
Reading a 500K binary file into a single var using binmode should be fine.
Below is a simple example, use unpack for multi-byte substrings. You can account for the difference between Intel byte order and Motorola byte order.

The relatively low level functions that I mentioned will "run like a rocket". 

#!/usr/bin/perl
use strict;
use warnings;


my $f = "31FCFFFFFFFFFFFE5817300618262527262123216E5D5346172D620000C00
+000000000000000262F2D2D2D2E2D00008000000150591200A832C001D02625222289
+3360808026187CFF";
$f = pack("H*",$f);

# substr EXPR,OFFSET,LENGTH,REPLACEMENT

print "Number of bytes: ", length $f, "\n";
printf "record Len? : %x  hex \n",ord(substr($f,0,1));
print  "record Len? : ", ord(substr($f,0,1))," decimal \n";
print  "not right first byte, ASCII '1':", substr($f,0,1),"\n"; ##ASCI
+I "1";

__END__
Prints:
Number of bytes: 73
record Len? : 31  hex 
record Len? : 49 decimal 
not right first byte, ASCII '1':1

[download]
I would be thinking of a subroutine that you call like: 
my $next_byte_index = process_record (\$data, $start_byte_index);

[download]
passing a reference to the data instead of the data itself will speed things up quite a bit.
To incorporate this into a loop, you will have to consider the "end conditions", when the loop ends and the difference between the length in bytes vs the "off by one" index number.

In reply to Re: How to find out, why my perl code is slow. by Marshall
in thread How to find out, why my perl code is slow. by Anonymous Monk

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