http://www.perlmonks.org?node_id=533433
fluffyvoidwarrior has asked for the wisdom of the Perl Monks concerning the following question:

Hi Monks, I'm having a spot of bother with Crypt::CBC in that it's slow and it bombs when faced with 700Mb of data to chain. I thought I'd have a bash at writing my own CBC thing. Currently I'm benchmarking parsing my data in 8 byte lumps for Blowfish and I can't improve on this code using substr().
$bufsize = length $buffer; for($chunk_counter = 0; $chunk_counter < $bufsize; $chu +nk_counter = $chunk_counter + 8){ $eight_byte_chunk = substr($buffer, $chunk_counter ,8) +; $out_buffer = $out_buffer . $eight_byte_chunk; } syswrite (OUTFILE,$out_buffer, $buffersize);
I'm sysreading the file into 64k buffers and then parsing the buffer in 8 byte lumps. I intend then to chain and blowfish it before syswriting the buffer back out to the encrypted file. I've tried various approaches and hoped unpack() would cut it but it's actually about 20% slower than the above. In the olden days I would have done this using a sliding pointer starting at the beginning of the buffer and incrementing it 8 bytes per read with an 8 byte data structure as the fastest method but I don't think you can do this in perl .. ? I'm sure there must be a more sophisticated method than substr.
Any "why not try this" suggestions are as always greatly appreciated.
Thanks