PDL::Types

Types(3pm)            User Contributed Perl Documentation           Types(3pm)



NAME
       PDL::Types - define fundamental PDL Datatypes

SYNOPSIS
        use PDL::Types;

        $pdl = ushort( 2.0, 3.0 );
        print "The actual c type used to store ushort's is '" .
           $pdl->type->realctype() . "'\n";
        The actual c type used to store ushort's is 'unsigned short'

DESCRIPTION
       Internal module - holds all the PDL Type info.  The type info can be
       accessed easily using the "PDL::Type" object returned by the type
       method.

       Skip to the end of this document to find out how to change the set of
       types supported by PDL.

Support functions
       A number of functions are available for module writers to get/process
       type information. These are used in various places (e.g. "PDL::PP",
       "PDL::Core") to generate the appropriate type loops, etc.

       typesrtkeys

       return array of keys of typehash sorted in order of type complexity

       ppdefs

       return array of pp symbols for all known types

       typefld

       return specified field ($fld) for specified type ($type) by querying
       type hash

       mapfld

       map a given source field to the corresponding target field by querying
       the type hash

       typesynonyms

       return type related synonym definitions to be included in pdl.h .  This
       routine must be updated to include new types as required.  Mostly the
       automatic updating should take care of the vital things.

PDL::Type OBJECTS
       This module declares one class - "PDL::Type" - objects of this class
       are returned by the type method of a piddle.  It has several methods,
       listed below, which provide an easy way to access type information:

       Additionally, comparison and stringification are overloaded so that you
       can compare and print type objects, e.g.

         $nofloat = 1 if $pdl->type < float;
         die "must be double" if $type != double;

       For further examples check again the type method.

       enum
           Returns the number representing this datatype (see get_datatype).

       symbol
           Returns one of 'PDL_B', 'PDL_S', 'PDL_US', 'PDL_L', 'PDL_LL',
           'PDL_F' or 'PDL_D'.

       ctype
           Returns the macro used to represent this type in C code (eg
           'PDL_Long').

       ppsym
           The letter used to represent this type in PP code code (eg 'U' for
           ushort).

       realctype
           The actual C type used to store this type.

       shortctype
           The value returned by "ctype" without the 'PDL_' prefix.

       badvalue
           Since PDL was compiled without support for 'bad' values, this rou-
           tine returns undef.

       orig_badvalue
           Since PDL was compiled without support for 'bad' values, this rou-
           tine returns undef.

Adding/removing types
       You can change the types that PDL knows about by editing entries in the
       definition of the variable @types that appears close to the top of the
       file Types.pm.PL (i.e. the file from which this module was generated).

       Format of a type entry

       Each entry in the @types array is a hash reference. Here is an example
       taken from the actual code that defines the "ushort" type:

                    {
                     identifier => 'US',
                     onecharident => 'U',   # only needed if different from identifier
                     pdlctype => 'PDL_Ushort',
                     realctype => 'unsigned short',
                     ppforcetype => 'ushort',
                     usenan => 0,
                     packtype => 'S*',
                    },

       Before we start to explain the fields please take this important mes-
       sage on board: entries must be listed in order of increasing complex-
       ity. This is critical to ensure that PDL"s type conversion works cor-
       rectly.  Basically, a less complex type will be converted to a more
       complex type as required.

       Fields in a type entry

       Each type entry has a number of required and optional entry.

       A list of all the entries:

       o   identifier

           Required. A short sequence of upercase letters that identifies this
           type uniquely. More than three characters is probably overkill.

       o   onecharident

           Optional. Only required if the "identifier" has more than one char-
           acter.  This should be a unique uppercase character that will be
           used to reference this type in PP macro expressions of the
           "TBSULFD" type. If you don't know what I am talking about read the
           PP manpage or ask on the mailing list.

       o   pdlctype

           Required. The "typedefed" name that will be used to access this
           type from C code.

       o   realctype

           Required. The C compiler type that is used to implement this type.
           For portability reasons this one might be platform dependent.

       o   ppforcetype

           Required. The type name used in PP signatures to refer to this
           type.

       o   usenan

           Required. Flag that signals if this type has to deal with NaN
           issues.  Generally only required for floating point types.

       o   packtype

           Required. The Perl pack type used to pack Perl values into the
           machine representation for this type. For details see "perldoc -f
           pack".

       Also have a look at the entries at the top of Types.pm.PL.

       The syntax is not written into stone yet and might change as the con-
       cept matures.

       Other things you need to do

       You need to check modules that do I/O (generally in the IO part of the
       directory tree). In the future we might add fields to type entries to
       automate this. This requires changes to those IO modules first though.

       You should also make sure that any type macros in PP files (i.e.
       "$TBSULFD...") are updated to reflect the new type. PDL::PP::Dump has a
       mode to check for type macros requiring updating. Do something like

           find . -name \*.pd -exec perl -Mblib=. -M'PDL::PP::Dump=typecheck' {} \;

       from the PDL root directory after updating Types.pm.PL to check for
       such places.



perl v5.8.8                       2002-05-21                        Types(3pm)