PDL::Types(3) 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 (in_value, in_key, out_key)

Map a given source field to the corresponding target field by querying the type hash. This gives you a way to say, "Find the type whose $in_key is equal to $value, and return that type's value for $out_key. For example: 

 # Does byte type use nan?
 $uses_nan = PDL::Types::mapfld(byte => 'ppforcetype', 'usenan');
 # Equivalent:
 $uses_nan = byte->usenan;
 
 # What is the actual C type for the value that we call 'long'?
 $type_name = PDL::Types::mapfld(long => 'convertfunc', 'realctype');
 # Equivalent:
 $type_name = long->realctype;

As you can see, the equivalent examples are much shorter and legible, so you should only use mapfld if you were given the type index (in which case the actual type is not immediately obvious): 

 $type_index = 4;
 $type_name = PDL::Types::mapfld($type_index => numval, 'realctype');

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.

datatypes_header

return C header text for pdl.h and pdlsimple.h.

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_IND', '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
The special numerical value used to represent bad values for this type. See badvalue routine in PDL::Bad for more details.
orig_badvalue
The default special numerical value used to represent bad values for this type. (You can change the value that represents bad values for each type during runtime.) See the orig_badvalue routine in PDL::Bad for more details.

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 message on board: entries must be listed in order of increasing complexity. This is critical to ensure that PDL's type conversion works correctly. 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:

  • identifier

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

  • onecharident

    Optional. Only required if the "identifier" has more than one character. 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.

  • pdlctype

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

  • realctype

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

  • ppforcetype

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

  • usenan

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

  • 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 concept 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.

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