Options¶

bignum recognizes some options that can be passed while loading it via use. The options can (currently) be either a single letter form, or the long form. The following options exist:

a or accuracy

This sets the accuracy for all math operations. The argument must be greater than or equal to zero. See Math::BigInt's bround() function for details.

        perl -Mbignum=a,50 -le 'print sqrt(20)'
    

Note that setting precision and accurary at the same time is not possible.

p or precision

This sets the precision for all math operations. The argument can be any integer. Negative values mean a fixed number of digits after the dot, while a positive value rounds to this digit left from the dot. 0 or 1 mean round to integer. See Math::BigInt's bfround() function for details.

        perl -Mbignum=p,-50 -le 'print sqrt(20)'
    

Note that setting precision and accurary at the same time is not possible.

t or trace

This enables a trace mode and is primarily for debugging bignum or Math::BigInt/Math::BigFloat.

l or lib

Load a different math lib, see "MATH LIBRARY".

        perl -Mbignum=l,GMP -e 'print 2 ** 512'
    

Currently there is no way to specify more than one library on the command line. This means the following does not work:

        perl -Mbignum=l,GMP,Pari -e 'print 2 ** 512'
    

This will be hopefully fixed soon ;)

hex

Override the built-in hex() method with a version that can handle big integers. Note that under Perl older than v5.9.4, this will be global and cannot be disabled with "no bigint;".

oct

Override the built-in oct() method with a version that can handle big integers. Note that under Perl older than v5.9.4, this will be global and cannot be disabled with "no bigint;".

v or version

This prints out the name and version of all modules used and then exits.

        perl -Mbignum=v
    

Methods¶

Beside import() and AUTOLOAD() there are only a few other methods.

Since all numbers are now objects, you can use all functions that are part of the BigInt or BigFloat API. It is wise to use only the bxxx() notation, and not the fxxx() notation, though. This makes it possible that the underlying object might morph into a different class than BigFloat.

Caveats¶

But a warning is in order. When using the following to make a copy of a number, only a shallow copy will be made.

        $x = 9; $y = $x;
        $x = $y = 7;

If you want to make a real copy, use the following:

        $y = $x->copy();

Using the copy or the original with overloaded math is okay, e.g. the following work:

        $x = 9; $y = $x;
        print $x + 1, " ", $y,"\n";     # prints 10 9

but calling any method that modifies the number directly will result in both the original and the copy being destroyed:

        $x = 9; $y = $x;
        print $x->badd(1), " ", $y,"\n";        # prints 10 10
        $x = 9; $y = $x;
        print $x->binc(1), " ", $y,"\n";        # prints 10 10
        $x = 9; $y = $x;
        print $x->bmul(2), " ", $y,"\n";        # prints 18 18

Using methods that do not modify, but test the contents works:

        $x = 9; $y = $x;
        $z = 9 if $x->is_zero();                # works fine

See the documentation about the copy constructor and "=" in overload, as well as the documentation in BigInt for further details.

inf()

A shortcut to return Math::BigInt->binf(). Useful because Perl does not always handle bareword "inf" properly.

NaN()

A shortcut to return Math::BigInt->bnan(). Useful because Perl does not always handle bareword "NaN" properly.

e

        # perl -Mbignum=e -wle 'print e'
    

Returns Euler's number "e", aka exp(1).

PI()

        # perl -Mbignum=PI -wle 'print PI'
    

Returns PI.

bexp()

        bexp($power,$accuracy);
    

Returns Euler's number "e" raised to the appropriate power, to the wanted accuracy.

Example:

        # perl -Mbignum=bexp -wle 'print bexp(1,80)'
    

bpi()

        bpi($accuracy);
    

Returns PI to the wanted accuracy.

Example:

        # perl -Mbignum=bpi -wle 'print bpi(80)'
    

upgrade()

Return the class that numbers are upgraded to, is in fact returning $Math::BigInt::upgrade.

in_effect()

        use bignum;
        print "in effect\n" if bignum::in_effect;       # true
        {
          no bignum;
          print "in effect\n" if bignum::in_effect;     # false
        }
    

Returns true or false if "bignum" is in effect in the current scope.

This method only works on Perl v5.9.4 or later.

Math Library¶

Math with the numbers is done (by default) by a module called Math::BigInt::Calc. This is equivalent to saying:

        use bignum lib => 'Calc';

You can change this by using:

        use bignum lib => 'GMP';

The following would first try to find Math::BigInt::Foo, then Math::BigInt::Bar, and when this also fails, revert to Math::BigInt::Calc:

        use bignum lib => 'Foo,Math::BigInt::Bar';

Please see respective module documentation for further details.

Using "lib" warns if none of the specified libraries can be found and Math::BigInt did fall back to one of the default libraries. To supress this warning, use "try" instead:

        use bignum try => 'GMP';

If you want the code to die instead of falling back, use "only" instead:

        use bignum only => 'GMP';

INTERNAL FORMAT¶

The numbers are stored as objects, and their internals might change at anytime, especially between math operations. The objects also might belong to different classes, like Math::BigInt, or Math::BigFLoat. Mixing them together, even with normal scalars is not extraordinary, but normal and expected.

You should not depend on the internal format, all accesses must go through accessor methods. E.g. looking at $x->{sign} is not a bright idea since there is no guaranty that the object in question has such a hashkey, nor is a hash underneath at all.

SIGN¶

The sign is either '+', '-', 'NaN', '+inf' or '-inf' and stored seperately. You can access it with the sign() method.

A sign of 'NaN' is used to represent the result when input arguments are not numbers or as a result of 0/0. '+inf' and '-inf' represent plus respectively minus infinity. You will get '+inf' when dividing a positive number by 0, and '-inf' when dividing any negative number by 0.