You may need a less than or equal to in the condition of the for loop. This probably won't make a difference in most cases, as the final probability is usually very small.

my $hypercdf = 0;
for (my $iref=$i; $iref <= min($N,$n); $iref++)
{
  $hypercdf += hypergeom($n,$m,$N,$iref);
}
print $hypercdf;
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