Re: Fast parsing for cypher block chaining

[Roy Johnson]

in reply to Fast parsing for cypher block chaining

I don't understand why you're putting 8 bytes at a time on the buffer. Is it just to ensure that you have an integer multiple of 8 bytes in your out_buffer? If so,

$bufsize = length $buffer;
# Make sure it's an integer multiple of 8 by reducing by any remainder
$bufsize -= $bufsize % 8;
#you could copy substr($buffer, 0, $bufsize) if you wanted/needed to
syswrite (OUTFILE, $buffer, $bufsize);

[ikegami]

"I intend then to chain and blowfish it before syswriting the buffer back out to the encrypted file.", the OP said. Blowfish only works on 8 bytes of data at a time, so the OP is looking for an efficient method of dividing a string into 8 byte segments.

[fluffyvoidwarrior]

cos Crypt::Blowfish works with 8 byte blocks. The disk reads and writes I'm doing in 64k chunks which seems about optimum. I'm then splitting the 64k buffer into 8 byte lumps for Blowfish.

[Roy Johnson]

I suspect you will do no worse letting Perl handle the buffering for you:

$/ = \8; # Read 8-byte records. Behind the scenes, Perl will do buffer
+ing of reads.
$out_buffer .= blowfishify($_) while <INFILE>;
print OUTFILE $out_buffer;

Alternatively, you could (with a sufficiently modern Perl) read from your buffer as if it were a filehandle, using the same $/ = \8 trick.

open BUF, '<', \$buffer or die "$!: Could not open buffer\n";
$/ = \8;
$out_buffer .= blowfishify($_) while <INFILE>;
print OUTFILE $out_buffer;

They're tidier ways of doing what you want, but you'd have to try them to see whether they buy or lose you any efficiency. My guess is that the I/O isn't going to be the bottleneck, anyway; the encryption is.

[ikegami]

In the first snippet, you should move the print into the loop to avoid using gigabytes of memory. That seemed to be the point of the OP's buffering.

$/ = \8; # Read 8-byte records. Behind the scenes, Perl will do buffer
+ing of reads.
print OUTFILE blowfishify($_)
   while <INFILE>;