To check whether the most significant bit positions of two unsigned integer values are equal (or both are zero), this works for me: 
sub msb_pos_is_equal {
    my ($x, $y) = @_;
    ($x ^ $y) <= ($x & $y)
}

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Update: Added the words "unsigned integer" in the first paragraph.

In reply to Re: reliable get position of leftmost bit in large integers by martin
in thread reliable get position of leftmost bit in large integers by wollmers

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