Re: 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, $bufsize);
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Re^2: Fast parsing for cypher block chaining by ikegami (Patriarch) on Feb 28, 2006 at 18:12 UTC
"I intend then to chain and blowfish it before syswriting the buffer back out to the encrypted file.", the OP said. Blowfish only works on 8 bytes of data at a time, so the OP is looking for an efficient method of dividing a string into 8 byte segments.	[reply]
Re^2: Fast parsing for cypher block chaining by fluffyvoidwarrior (Monk) on Feb 28, 2006 at 18:13 UTC
cos Crypt::Blowfish works with 8 byte blocks. The disk reads and writes I'm doing in 64k chunks which seems about optimum. I'm then splitting the 64k buffer into 8 byte lumps for Blowfish.	[reply]
Re^3: Fast parsing for cypher block chaining by Roy Johnson (Monsignor) on Feb 28, 2006 at 18:25 UTC
I suspect you will do no worse letting Perl handle the buffering for you: `$/ = \8; # Read 8-byte records. Behind the scenes, Perl will do buffer +ing of reads. $out_buffer .= blowfishify($_) while <INFILE>; print OUTFILE $out_buffer;` [download] Alternatively, you could (with a sufficiently modern Perl) read from your buffer as if it were a filehandle, using the same `$/ = \8` trick. `open BUF, '<', \$buffer or die "$!: Could not open buffer\n"; $/ = \8; $out_buffer .= blowfishify($_) while <INFILE>; print OUTFILE $out_buffer;` [download] They're tidier ways of doing what you want, but you'd have to try them to see whether they buy or lose you any efficiency. My guess is that the I/O isn't going to be the bottleneck, anyway; the encryption is. Caution: Contents may have been coded under pressure.	[reply] [d/l] [select]
Re^4: Fast parsing for cypher block chaining by ikegami (Patriarch) on Feb 28, 2006 at 18:41 UTC
In the first snippet, you should move the `print` into the loop to avoid using gigabytes of memory. That seemed to be the point of the OP's buffering. `$/ = \8; # Read 8-byte records. Behind the scenes, Perl will do buffer +ing of reads. print OUTFILE blowfishify($_) while <INFILE>;` [download]	[reply] [d/l] [select]