unixdev.net


Switch to SpeakEasy.net DSL

The Modular Manual Browser

Home Page
Manual: (OpenBSD-3.6)
Page:
Section:
Apropos / Subsearch:
optional field



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

DESCRIPTION
       All operators (including basic math operations) are over-
       loaded. 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 neccessary:

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

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




perl v5.8.5                 2002-11-06                          1





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


       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->binc();'
               perl -Mbignum -le 'print 1234->binc->badd(6);'
               perl -Mbignum -le 'print +(1234)->binc()'

       (Note that print doesn't do what you expect if the expres-
       sion starts with '(' hence the "+")

       You can even chain the operations together as usual:

               perl -Mbignum -le 'print 1234->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

       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,



perl v5.8.5                 2002-11-06                          2





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


       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)'

       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)'

       t or trace
         This enables a trace mode and is primarily for debugging
         bignum or Math::BigInt/Math::BigFloat.

       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 will be hopefully
         fixed soon ;)

       v or version
         This prints out the name and version of all modules used
         and then exits.

                 perl -Mbignum=v -e ''



perl v5.8.5                 2002-11-06                          3





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


       METHODS

       Beside import() and AUTOLOAD() there are only a few other
       methods.

       Since all numbers are now objects, you can use all func-
       tions 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 underly-
       ing object might morph into a different class than
       BigFloat.

       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 beeing
       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.

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




perl v5.8.5                 2002-11-06                          4





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


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

         upgrade()
           Return the class that numbers are upgraded to, is in
           fact returning $Math::BigInt::upgrade.

         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 => 'BitVect';

         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.

         INTERNAL FORMAT

         The numbers are stored as objects, and their internals
         might change at anytime, especially between math opera-
         tions. The objects also might belong to different
         classes, like Math::BigInt, or Math::BigFLoat. Mixing
         them together, even with normal scalars is not extraor-
         dinary, 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



perl v5.8.5                 2002-11-06                          5





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


         number by 0, and '-inf' when dividing any negative num-
         ber by 0.

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 2 ** 0.5'
               perl -Mbignum=a,65 -le 'print 2 ** 0.2'

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, 2003.















perl v5.8.5                 2002-11-06                          6