Perl Weekly Challenge W029 - Calling C | Yet, Another Perl Hacker

The second task for this week’s challenge is to write a script to demostrate calling a C function in perl, it can be a user-defined or a standard(built-in) C function.

I have seen implementation of this using the Inline module but I have to be honest that I have never really tried it in perl. Never had the need to use it or atleast that’s what I thought. At the back of my mind, I knew a piece of code compiled in C would perform better compared to pure perl solution.

Solution:

So for this task, I created a fibonacci function (both in C and perl) that would take a number $n as input and would return the n-th number in the fibonacci series.

I used the Inline module and wrote the C function after the special literals __END__ and __C__.

__END__ indicates the logical end of the script before the actual end of file. Any following text is ignored.
__C__ indicates the start of the C code

The perl_fib function is the pure perl version of the fibonacci function and fib is the C version.

I knew the perl implementation would take longer to finish (vs C) on bigger input range; so I took the oppurtunity to use the Memoize module to compare the performaces of:

perl_fib - function writtern in perl without Memoize
perl_fib(Memoized) - same function but Memoized
fib - function written in C

Code:

#!/usr/bin/env perl
# Write a script to demonstrate calling a C function. 
# It could be any user defined or standard C function.
use strict;
use warnings;
use feature 'say';
use Memoize;

use Inline 'C';

my $start_run;
my $run_time;


$start_run = time();
print (perl_fib($_)." ") for 1..36;
$run_time  = time() - $start_run;
say "\nRun Time (Perl): $run_time sec\n";

memoize('perl_fib');
$start_run = time();
print (perl_fib($_)." ") for 1..36;
$run_time  = time() - $start_run;
say "\nRun Time (Perl-Memoized): $run_time sec\n";

$start_run = time();
print (fib($_)." ") for 1..36;
$run_time  = time() - $start_run;
say "\nRun Time (Inline-C): $run_time sec\n";

sub perl_fib { (
    $_[0] == 0) ? 
        0: ($_[0] == 1)?
            1:perl_fib($_[0]-1)+perl_fib($_[0]-2)
}

__END__
__C__
unsigned long fib(int n) {
    if ( n == 0 )
        return 0;
    else if ( n == 1 )
        return 1;
    else
        return ( fib(n-1) + fib(n-2) );
}

Output:

perl ch-2.pl 
1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 1597 2584 4181 6765 10946 17711 28657 46368 75025 
121393 196418 317811 514229 832040 1346269 2178309 3524578 5702887 9227465 14930352 
Run Time (Perl): 49 sec

1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 1597 2584 4181 6765 10946 17711 28657 46368 75025 
121393 196418 317811 514229 832040 1346269 2178309 3524578 5702887 9227465 14930352 
Run Time (Perl-Memoized): 0 sec

1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 1597 2584 4181 6765 10946 17711 28657 46368 75025 
121393 196418 317811 514229 832040 1346269 2178309 3524578 5702887 9227465 14930352 
Run Time (Inline-C): 1 sec

As expected, the perl implementation took the longer compared to the C version. But it is surprising how Memoize cut down the execution time to just a fraction of a second.

And that’s it for this week’s challenge. If you’d like to join the fun and contribute, please visit the site managed by Mohammad S Anwar.