You are viewing the version of this documentation from Perl 5.38.2. View the latest version

CONTENTS

NAME

bigfloat - transparent big floating point number support for Perl

SYNOPSIS

use bigfloat;

$x = 2 + 4.5;                       # Math::BigFloat 6.5
print 2 ** 512 * 0.1;               # Math::BigFloat 134...09.6
print inf + 42;                     # Math::BigFloat inf
print NaN * 7;                      # Math::BigFloat NaN
print hex("0x1234567890123490");    # Perl v5.10.0 or later

{
    no bigfloat;
    print 2 ** 256;                 # a normal Perl scalar now
}

# for older Perls, import into current package:
use bigfloat qw/hex oct/;
print hex("0x1234567890123490");
print oct("01234567890123490");

DESCRIPTION

All numeric literals in the given scope are converted to Math::BigFloat objects.

All operators (including basic math operations) except the range operator .. are overloaded.

So, the following:

use bigfloat;
$x = 1234;

creates a Math::BigFloat and stores a reference to in $x. This happens transparently and behind your back, so to speak.

You can see this with the following:

perl -Mbigfloat -le 'print ref(1234)'

Since numbers are actually objects, you can call all the usual methods from Math::BigFloat on them. This even works to some extent on expressions:

perl -Mbigfloat -le '$x = 1234; print $x->bdec()'
perl -Mbigfloat -le 'print 1234->copy()->binc();'
perl -Mbigfloat -le 'print 1234->copy()->binc->badd(6);'
perl -Mbigfloat -le 'print +(1234)->copy()->binc()'

(Note that print doesn't do what you expect if the expression starts with '(' hence the +)

You can even chain the operations together as usual:

perl -Mbigfloat -le 'print 1234->copy()->binc->badd(6);'
1241

Please note the following does not work as expected (prints nothing), since overloading of '..' is not yet possible in Perl (as of v5.8.0):

perl -Mbigfloat -le 'for (1..2) { print ref($_); }'

Options

bigfloat recognizes some options that can be passed while loading it via 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 -Mbigfloat=a,50 -le 'print sqrt(20)'

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, while 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 -Mbigfloat=p,-50 -le 'print sqrt(20)'

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 -Mbigfloat=l,GMP -e 'print 2 ** 512'
perl -Mbigfloat=lib,GMP -e 'print 2 ** 512'
perl -Mbigfloat=try,GMP -e 'print 2 ** 512'
perl -Mbigfloat=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 bigfloat 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 bigfloat pragma is active.

v or version

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

perl -Mbigfloat=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 bigfloat lib => 'Calc';

you can change this by using:

use bigfloat 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 bigfloat 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 bigfloat try => 'GMP';

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

use bigfloat only => 'GMP';

Please see 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::BigFloat 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::BigFloat for further details.

Methods

inf()

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

NaN()

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

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

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

PI
# perl -Mbigfloat=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 -Mbigfloat=bexp -wle 'print bexp(1,80)'
bpi()
bpi($accuracy);

Returns PI to the wanted accuracy.

Example:

# perl -Mbigfloat=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.

upgrade()

Set or get the class that the downgrade class upgrades to, if any. Set the upgrade class to undef to disable upgrading.

Upgrading is disabled by default.

downgrade()

Set or get the class that the upgrade class downgrades to, if any. Set the downgrade class to undef to disable upgrading.

Downgrading is disabled by default.

in_effect()
use bigfloat;

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

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

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

CAVEATS

Hexadecimal, octal, and binary floating point literals

Perl (and this module) accepts hexadecimal, octal, and binary floating point literals, but use them with care with Perl versions before v5.32.0, because some versions of Perl silently give the wrong result.

Operator vs literal overloading

bigrat works by overloading handling of integer and floating point literals, converting them to Math::BigRat objects.

This means that arithmetic involving only string values or string literals are performed using Perl's built-in operators.

For example:

use bigrat;
my $x = "900000000000000009";
my $y = "900000000000000007";
print $x - $y;

outputs 0 on default 32-bit builds, since bigfloat never sees the string literals. To ensure the expression is all treated as Math::BigFloat objects, use a literal number in the expression:

print +(0+$x) - $y;
Ranges

Perl does not allow overloading of ranges, so you can neither safely use ranges with bigfloat endpoints, nor is the iterator variable a Math::BigFloat.

use 5.010;
for my $i (12..13) {
  for my $j (20..21) {
    say $i ** $j;  # produces a floating-point number,
                   # not an object
  }
}
in_effect()

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

hex()/oct()

bigfloat overrides these routines with versions that can also handle big integer values. Under Perl prior to version v5.9.4, however, this will not happen unless you specifically ask for it with the two import tags "hex" and "oct" - and then it will be global and cannot be disabled inside a scope with no bigfloat:

use bigfloat qw/hex oct/;

print hex("0x1234567890123456");
{
    no bigfloat;
    print hex("0x1234567890123456");
}

The second call to hex() will warn about a non-portable constant.

Compare this to:

use bigfloat;

# will warn only under Perl older than v5.9.4
print hex("0x1234567890123456");

EXAMPLES

Some cool command line examples to impress the Python crowd ;)

perl -Mbigfloat -le 'print sqrt(33)'
perl -Mbigfloat -le 'print 2**255'
perl -Mbigfloat -le 'print 4.5+2**255'
perl -Mbigfloat -le 'print 3/7 + 5/7 + 8/3'
perl -Mbigfloat -le 'print 123->is_odd()'
perl -Mbigfloat -le 'print log(2)'
perl -Mbigfloat -le 'print exp(1)'
perl -Mbigfloat -le 'print 2 ** 0.5'
perl -Mbigfloat=a,65 -le 'print 2 ** 0.2'
perl -Mbigfloat=l,GMP -le 'print 7 ** 7777'

BUGS

Please report any bugs or feature requests to bug-bignum at rt.cpan.org, or through the web interface at https://rt.cpan.org/Ticket/Create.html?Queue=bignum (requires login). We will be notified, and then you'll automatically be notified of progress on your bug as I make changes.

SUPPORT

You can find documentation for this module with the perldoc command.

perldoc bigfloat

You can also look for information at:

LICENSE

This program is free software; you may redistribute it and/or modify it under the same terms as Perl itself.

SEE ALSO

bigint and bigrat.

Math::BigInt, Math::BigFloat, Math::BigRat and Math::Big as well as Math::BigInt::FastCalc, Math::BigInt::Pari and Math::BigInt::GMP.

AUTHORS