I do not intend any personal offense, but I am compelled to say that it is absurd to tell someone that they will realize a 440x runtime improvement without any knowledge of their task, their code, or their hardware.

If the code isn't CPU-bound, the performance gain will be negligible.

Your example, by the way, of cryptographic hashing, is just the type of task that does benefit greatly from using a lower-level language. However, switching to C won't yield the massive improvements you describe because the folks who implement perl's widely-used crypto modules are already using C.

To demonstrate, on an ancient Pentium II system running at 350 MHz, let's hash all the executables in my /usr/bin directory.

Version of sha1sum (a C program):

Code:

$ sha1sum --version | head -n1
sha1sum (GNU coreutils) 5.97

Perl script:

Code:

$ cat sha1.pl
use Digest::SHA1;
binmode(STDIN);
my $s = Digest::SHA1->new;
while (read(STDIN, $buf, 1024)) {
    $s->add($buf);
}
print $s->hexdigest . "\n"

Creating data file:

Code:

$ for f in /usr/bin/*; do cat "$f"; done > usr.bin 2> /dev/null
$ stat --printf '%s\n' usr.bin  # ~ 181 MB
189537836

Comparison:

Code:

$ time sha1sum < usr.bin
bb02b0a0c08a1b4070f97035f0ad5f7f2c491c78  -

real    0m13.622s
user    0m10.217s
sys     0m1.868s
$ time perl sha1.pl < usr.bin
bb02b0a0c08a1b4070f97035f0ad5f7f2c491c78

real    0m17.131s
user    0m12.733s
sys     0m1.604s

The tests were repeated several times in different orders. The times never varied significantly. 1.25x faster is a far, far cry from 440x. The small improvement is expected since both are hashing in C.

It is reasonable to conclude that whatever perl script you were using (or the modifications made to it) was seriously deficient.

Regards,
Alister

---------- Post updated at 12:43 PM ---------- Previous update was at 12:34 PM ----------

For i/o and string comparisons and the like, the improvement ratio (perl-time/c-time) will be small. However, if the dataset is massive, that ratio could amount to a substantial speedup. The 1.25x improvement in the sha1 hashing in my previous post isn't much for 181 MB of data, 3.5 secs or so, but it's about 20 seconds per gigabyte and 5.5 hours per terabyte.

Regards,
Alister