use Math::BigInt;

$i = Math::BigInt->new($string);

# BINT is a big integer string; in all following cases $i remains unchanged.
# All methods except bcmp() return a big integer string, or strings.
$i->bneg;       # return negative of $i
$i->babs        # return absolute value of $i
$i->bcmp(BINT)  # compare $i to BINT; see below for return value
$i->badd(BINT)  # return sum of BINT and $i
$i->bsub(BINT)  # return $i minus BINT
$i->bmul(BINT)  # return $i multiplied by BINT
$i->bdiv(BINT)  # return $i divided by BINT; see below for return value
$i->bmod(BINT)  # return $i modulus BINT
$i->bgcd(BINT)  # return greatest common divisor of $i and BINT
$i->bnorm       # return normalization of $i
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'+0'                # canonical zero value
'   -123 123 123'   # canonical value:  '-123123123'
'1 23 456 7890'     # canonical value:  '+1234567890'
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$a = Math::BigInt->new("42 000 000 000 000");
$b = Math::BigInt->new("-111111");
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$c = 42000000000000 - -111111;
                          # 42000000111111; ordinary math--$c is a double
$c = $a - $b;             # "+42000000111111"; $c is now a BigInt object
$c = $a - -111111;        # "+42000000111111"; $c is now a BigInt object
$c = $a->bsub($b);        # "+42000000111111"; $c is just a string
$c = $a->bsub(-111111);   # "+42000000111111"; $c is just a string