bigfloat(3perl) Perl Programmers Reference Guide bigfloat(3perl)
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:
• GitHub
<https://github.com/pjacklam/p5-bignum>
• RT: CPAN's request tracker
<https://rt.cpan.org/Dist/Display.html?Name=bignum>
• MetaCPAN
<https://metacpan.org/release/bignum>
• CPAN Testers Matrix
<http://matrix.cpantesters.org/?dist=bignum>
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
• (C) by Tels <http://bloodgate.com/> in early 2002 - 2007.
• Maintained by Peter John Acklam <pjacklam@gmail.com>, 2014-.
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