bigint(3pm) Perl Programmers Reference Guide bigint(3pm)
NAME
bigint - Transparent BigInteger support for Perl
SYNOPSIS
use bigint;
$x = 2 + 4.5,"\n"; # BigInt 6
print 2 ** 512,"\n"; # really is what you think it is
print inf + 42,"\n"; # inf
print NaN * 7,"\n"; # NaN
print hex("0x1234567890123490"),"\n"; # Perl v5.9.4 or later
{
no bigint;
print 2 ** 256,"\n"; # a normal Perl scalar now
}
# Note that this will be global:
use bigint qw/hex oct/;
print hex("0x1234567890123490"),"\n";
print oct("01234567890123490"),"\n";
DESCRIPTION
All operators (including basic math operations) are overloaded. Integer
constants are created as proper BigInts.
Floating point constants are truncated to integer. All parts and
results of expressions are also truncated.
Unlike integer, this pragma creates integer constants that are only
limited in their size by the available memory and CPU time.
use integer vs. use bigint
There is one small difference between "use integer" and "use bigint":
the former will not affect assignments to variables and the return
value of some functions. "bigint" truncates these results to integer
too:
# 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 makes seldom a difference as parts and results of
expressions will be 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 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 -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 <B>ignored</B> since all operations happen in integer
space. A positive value rounds to this digit left from the dot. 0 or
1 mean round to integer and are ignore like negative values.
See Math::BigInt's bfround() function for details.
perl -Mbignum=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 bigint or
Math::BigInt.
hex
Override the built-in hex() method with a version that can handle big
integers. Note that under Perl v5.9.4 or ealier, 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 v5.9.4 or ealier, this will be global
and cannot be disabled with "no bigint;".
l, lib, try or only
Load a different math lib, see "Math Library".
perl -Mbigint=lib,GMP -e 'print 2 ** 512'
perl -Mbigint=try,GMP -e 'print 2 ** 512'
perl -Mbigint=only,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 ;)
v or version
This prints out the name and version of all modules used and then
exits.
perl -Mbigint=v
Math Library
Math with the numbers is done (by default) by a module called
Math::BigInt::Calc. This is equivalent to saying:
use bigint 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 bigint lib => 'Foo,Math::BigInt::Bar';
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
suppress 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';
Please see respective module documentation for further details.
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::BigInt::Lite.
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 $x->{sign} is not a good idea
since there is no guaranty that the object in question has such a hash
key, nor is a hash underneath at all.
Sign
The sign is either '+', '-', 'NaN', '+inf' or '-inf'. You can access
it with the sign() method.
A sign of 'NaN' is used to represent the result when input arguments
are not numbers or as a result of 0/0. '+inf' and '-inf' represent plus
respectively minus infinity. You will get '+inf' when dividing a
positive number by 0, and '-inf' when dividing any negative number by
0.
Methods
Since all numbers are now objects, you can use all functions that are
part of the BigInt API. You can only use the bxxx() notation, and not
the fxxx() notation, though.
inf()
A shortcut to return Math::BigInt->binf(). Useful because Perl does
not always handle bareword "inf" properly.
NaN()
A shortcut to return Math::BigInt->bnan(). Useful because Perl does
not always handle bareword "NaN" properly.
e
# perl -Mbigint=e -wle 'print e'
Returns Euler's number "e", aka exp(1). Note that under bigint, this
is truncated to an integer, and hence simple '2'.
PI
# perl -Mbigint=PI -wle 'print PI'
Returns PI. Note that under bigint, this is truncated to an integer,
and hence simple '3'.
bexp()
bexp($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, and hence simple '3'.
Example:
# perl -Mbigint=bpi -wle 'print bpi(80)'
upgrade()
Return the class that numbers are upgraded to, is in fact returning
$Math::BigInt::upgrade.
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.
MATH LIBRARY
Math with the numbers is done (by default) by a module called
Caveat
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 testthe 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.
CAVEATS
in_effect()
This method only works on Perl v5.9.4 or later.
hex()/oct()
"bigint" 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 bigint":
use bigint qw/hex oct/;
print hex("0x1234567890123456");
{
no bigint;
print hex("0x1234567890123456");
}
The second call to hex() will warn about a non-portable constant.
Compare this to:
use bigint;
# will warn only under Perl older than v5.9.4
print hex("0x1234567890123456");
MODULES USED
"bigint" is just a thin wrapper around various modules of the
Math::BigInt family. Think of it as the head of the family, who runs
the shop, and orders the others to do the work.
The following modules are currently used by bigint:
Math::BigInt::Lite (for speed, and only if it is loadable)
Math::BigInt
EXAMPLES
Some cool command line examples to impress the Python crowd ;) You
might want to compare them to the results under -Mbignum or -Mbigrat:
perl -Mbigint -le 'print sqrt(33)'
perl -Mbigint -le 'print 2*255'
perl -Mbigint -le 'print 4.5+2*255'
perl -Mbigint -le 'print 3/7 + 5/7 + 8/3'
perl -Mbigint -le 'print 123->is_odd()'
perl -Mbigint -le 'print log(2)'
perl -Mbigint -le 'print 2 ** 0.5'
perl -Mbigint=a,65 -le 'print 2 ** 0.2'
perl -Mbignum=a,65,l,GMP -le 'print 7 ** 7777'
LICENSE
This program is free software; you may redistribute it and/or modify it
under the same terms as Perl itself.
SEE ALSO
Especially bigrat as in "perl -Mbigrat -le 'print 1/3+1/4'" and bignum
as in "perl -Mbignum -le 'print sqrt(2)'".
Math::BigInt, Math::BigRat and Math::Big as well as
Math::BigInt::BitVect, Math::BigInt::Pari and Math::BigInt::GMP.
AUTHORS
(C) by Tels <http://bloodgate.com/>; in early 2002 - 2007.
perl v5.16.3 2013-03-04 bigint(3pm)
Linux-Distributionen
Huschi als Linux-Admin