use integer vs. use bigint

There are some difference between "use integer" and "use bigint".

Whereas "use integer" is limited to what can be handled as a Perl scalar, "use bigint" can handle arbitrarily large integers.

Also, "use integer" does affect assignments to variables and the return value of some functions. "use bigint" truncates these results to integer:

    # perl -Minteger -wle 'print 3.2'
    3.2
    # perl -Minteger -wle 'print 3.2 + 0'
    3
    # perl -Mbigint -wle 'print 3.2'
    3
    # perl -Mbigint -wle 'print 3.2 + 0'
    3
    # perl -Mbigint -wle 'print exp(1) + 0'
    2
    # perl -Mbigint -wle 'print exp(1)'
    2
    # perl -Minteger -wle 'print exp(1)'
    2.71828182845905
    # perl -Minteger -wle 'print exp(1) + 0'
    2

In practice this seldom makes a difference for small integers as parts and results of expressions are truncated anyway, but this can, for instance, affect the return value of subroutines:

    sub three_integer { use integer; return 3.2; }
    sub three_bigint { use bigint; return 3.2; }
    print three_integer(), " ", three_bigint(),"\n";    # prints "3.2 3"

Options

"bigint" recognizes some options that can be passed while loading it via "use". 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() method for details.

    perl -Mbigint=a,2 -le 'print 12345+1'
    

Note that setting precision and accuracy 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, and are ignored since all operations happen in integer space. A positive value rounds to this digit left from the dot. 0 means round to integer. See Math::BigInt's bfround() method for details.

    perl -mbigint=p,5 -le 'print 123456789+123'
    

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

t or trace

This enables a trace mode and is primarily for debugging.

l, lib, try, or only

Load a different math lib, see "Math Library".

    perl -Mbigint=l,GMP -e 'print 2 ** 512'
    perl -Mbigint=lib,GMP -e 'print 2 ** 512'
    perl -Mbigint=try,GMP -e 'print 2 ** 512'
    perl -Mbigint=only,GMP -e 'print 2 ** 512'
    

hex

Override the built-in hex() method with a version that can handle big numbers. This overrides it by exporting it to the current package. Under Perl v5.10.0 and higher, this is not so necessary, as hex() is lexically overridden in the current scope whenever the "bigint" pragma is active.

oct

Override the built-in oct() method with a version that can handle big numbers. This overrides it by exporting it to the current package. Under Perl v5.10.0 and higher, this is not so necessary, as oct() is lexically overridden in the current scope whenever the "bigint" pragma is active.

v or version

this prints out the name and version of the modules and then exits.

    perl -Mbigint=v
    

Math Library

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

    use bigint lib => 'Calc';

you can change this by using:

    use bigint lib => 'GMP';

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

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

Using c<lib> warns if none of the specified libraries can be found and Math::BigInt fell back to one of the default libraries. To suppress this warning, use c<try> instead:

    use bigint try => 'GMP';

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

    use bigint only => 'GMP';

Please see the respective module documentation for further details.

Method calls

Since all numbers are now objects, you can use all methods that are part of the Math::BigInt API.

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;

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 that 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 Math::BigInt for further details.

Methods

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 -Mbigint=e -wle 'print e'
    

Returns Euler's number "e", aka exp(1). Note that under "bigint", this is truncated to an integer, i.e., 2.

PI

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

Returns PI. Note that under "bigint", this is truncated to an integer, i.e., 3.

bexp()

    bexp($power, $accuracy);
    

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

Note that under "bigint", the result is truncated to an integer.

Example:

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

bpi()

    bpi($accuracy);
    

Returns PI to the wanted accuracy. Note that under "bigint", this is truncated to an integer, i.e., 3.

Example:

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

accuracy()

Set or get the accuracy.

precision()

Set or get the precision.

round_mode()

Set or get the rounding mode.

div_scale()

Set or get the division scale.

in_effect()

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

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

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