Does it give the proper results? As in the old version I'm using, blsft() appears to return a string not a bigint object, $result += $tmp; might not do the proper thing.

use Math::BigInt;
use Data::Dumper;
print Dumper +Math::BigInt->new(1)->blsft(8);
print $Math::BigInt::VERSION;
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Result:

$VAR1 = '+256';
0.01
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OTOH, $tmp is a bigint object. Hmm...

OK, no reason to panic:

$result = 1;
$result += new Math::BigInt('1234567890' x 10);
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does seem to work alright.