print sqrt($_), "\t", mysqrt($_, .0000001), "\n" for qw/.25 .50 .75 1 10 50 100 1000 31415926/; sub mysqrt { my ($tgt, $err, $try, $len) = @_; return 1 if $tgt == 1; if (! defined $try) { ($len, $try) = $tgt < 1 ? ((1 - $tgt) / 2, $tgt + (1 - $tgt) / 2) : ($tgt / 2, $tgt / 2); return mysqrt($tgt, $err, $try, $len); } my $dif = $tgt - ($try * $try); return $try if abs($dif) < $err; $len /= 2; $try = $dif > 0 ? $try + $len : $try - $len; return mysqrt($tgt, $err, $try, $len); }