


bignum(3p)       Perl Programmers Reference Guide      bignum(3p)


NAME
       bignum - Transparent BigNumber support for Perl

SYNOPSIS
         use bignum;

         $x = 2 + 4.5,"\n";                    # BigFloat 6.5
         print 2 ** 512 * 0.1,"\n";            # really is what you think it is
         print inf * inf,"\n";                 # prints inf
         print NaN * 3,"\n";                   # prints NaN

         {
           no bignum;
           print 2 ** 256,"\n";                # a normal Perl scalar now
         }

         # for older Perls, note that this will be global:
         use bignum qw/hex oct/;
         print hex("0x1234567890123490"),"\n";
         print oct("01234567890123490"),"\n";

DESCRIPTION
       All operators (including basic math operations) are
       overloaded. Integer and floating-point constants are
       created as proper BigInts or BigFloats, respectively.

       If you do

               use bignum;

       at the top of your script, Math::BigFloat and Math::BigInt
       will be loaded and any constant number will be converted
       to an object (Math::BigFloat for floats like 3.1415 and
       Math::BigInt for integers like 1234).

       So, the following line:

               $x = 1234;

       creates actually a Math::BigInt 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 -Mbignum -le 'print ref(1234)'

       Don't worry if it says Math::BigInt::Lite, bignum and
       friends will use Lite if it is installed since it is
       faster for some operations. It will be automatically
       upgraded to BigInt whenever necessary:

               perl -Mbignum -le 'print ref(2**255)'




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bignum(3p)       Perl Programmers Reference Guide      bignum(3p)


       This also means it is a bad idea to check for some
       specific package, since the actual contents of $x might be
       something unexpected. Due to the transparent way of bignum
       "ref()" should not be necessary, anyway.

       Since Math::BigInt and BigFloat also overload the normal
       math operations, the following line will still work:

               perl -Mbignum -le 'print ref(1234+1234)'

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

               perl -Mbignum -le '$x = 1234; print $x->bdec()'
               perl -Mbignum -le 'print 1234->copy()->binc();'
               perl -Mbignum -le 'print 1234->copy()->binc->badd(6);'
               perl -Mbignum -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 -Mbignum -le 'print 1234->copy()->binc->badd(6);'
               1241

       Under bignum (or bigint or bigrat), Perl will "upgrade"
       the numbers appropriately. This means that:

               perl -Mbignum -le 'print 1234+4.5'
               1238.5

       will work correctly. These mixed cases don't do always
       work when using Math::BigInt or Math::BigFloat alone, or
       at least not in the way normal Perl scalars work.

       If you do want to work with large integers like under "use
       integer;", try "use bigint;":

               perl -Mbigint -le 'print 1234.5+4.5'
               1238

       There is also "use bigrat;" which gives you big rationals:

               perl -Mbigrat -le 'print 1234+4.1'
               12381/10

       The entire upgrading/downgrading is still experimental and
       might not work as you expect or may even have bugs. You
       might get errors like this:

               Can't use an undefined value as an ARRAY reference at
               /usr/local/lib/perl5/5.8.0/Math/BigInt/Calc.pm line 864



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bignum(3p)       Perl Programmers Reference Guide      bignum(3p)


       This means somewhere a routine got a BigFloat/Lite but
       expected a BigInt (or vice versa) and the upgrade/downgrad
       path was missing. This is a bug, please report it so that
       we can fix it.

       You might consider using just Math::BigInt or
       Math::BigFloat, since they allow you finer control over
       what get's done in which module/space. For instance,
       simple loop counters will be Math::BigInts under "use
       bignum;" and this is slower than keeping them as Perl
       scalars:

               perl -Mbignum -le 'for ($i = 0; $i < 10; $i++) { print ref($i); }'

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

   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.





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bignum(3p)       Perl Programmers Reference Guide      bignum(3p)


       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



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bignum(3p)       Perl Programmers Reference Guide      bignum(3p)


       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.




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bignum(3p)       Perl Programmers Reference Guide      bignum(3p)


         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:



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bignum(3p)       Perl Programmers Reference Guide      bignum(3p)


               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.

CAVAETS
       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.



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bignum(3p)       Perl Programmers Reference Guide      bignum(3p)


         Compare this to:

                 use bigint;

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

MODULES USED
       "bignum" 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 bignum:

               Math::BigInt::Lite      (for speed, and only if it is loadable)
               Math::BigInt
               Math::BigFloat

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

               perl -Mbignum -le 'print sqrt(33)'
               perl -Mbignum -le 'print 2*255'
               perl -Mbignum -le 'print 4.5+2*255'
               perl -Mbignum -le 'print 3/7 + 5/7 + 8/3'
               perl -Mbignum -le 'print 123->is_odd()'
               perl -Mbignum -le 'print log(2)'
               perl -Mbignum -le 'print exp(1)'
               perl -Mbignum -le 'print 2 ** 0.5'
               perl -Mbignum=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'".

       Math::BigFloat, 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.









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