I timed those two functions along with the following: 
sub by_string {
  my $n = shift;
  return length(sprintf "%b", $n) - 1;
}

[download]
I tested with high bits using int rand(2**64), medium bits int rand(2**32) and lower bits int rand(2**16) for 1e6 iterations. 
log    linear sprintf
0.2917 0.4427 0.3370  avg_sig=62
0.2786 2.8430 0.3056  avg_sig=30
0.2826 4.1060 0.2986  avg_sig=14

[download]

In reply to Re^2: Most Significant Set Bit by Danny
in thread Most Significant Set Bit by coldr3ality

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