In the perl portion, I think this line:

$elapsed_c = tv_interval($start_time,$end_time);
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should be this:

$elapsed_c = tv_interval($start_time_c,$end_time_c);
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and

$elapsed_perl = tv_interval($start_time,$end_time);
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should be:

$elapsed_perl = tv_interval($start_time_perl,$end_time_perl);
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Note that $start_time and $end_time are never declared, nor initialized, and a "use strict;" at the top would have helped you spot this.