Conversion.h

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// # Conversion.h: A class with general conversion definitions
// # Copyright (C) 1996,1999,2001,2002,2003
// # Associated Universities, Inc. Washington DC, USA.
// #
// # This library is free software; you can redistribute it and/or modify it
// # under the terms of the GNU Library General Public License as published by
// # the Free Software Foundation; either version 2 of the License, or (at your
// # option) any later version.
// #
// # This library is distributed in the hope that it will be useful, but WITHOUT
// # ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
// # FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Library General Public
// # License for more details.
// #
// # You should have received a copy of the GNU Library General Public License
// # along with this library; if not, write to the Free Software Foundation,
// # Inc., 675 Massachusetts Ave, Cambridge, MA 02139, USA.
// #
// # Correspondence concerning AIPS++ should be addressed as follows:
// #        Internet email: casa-feedback@nrao.edu.
// #        Postal address: AIPS++ Project Office
// #                        National Radio Astronomy Observatory
// #                        520 Edgemont Road
// #                        Charlottesville, VA 22903-2475 USA
 
#ifndef CASA_CONVERSION_H
#define CASA_CONVERSION_H
 
// # Includes
#include <casacore/casa/aips.h>
#include <casacore/casa/string.h>  // needed for memcpy
 
namespace casacore {  // # NAMESPACE CASACORE - BEGIN
 
// <summary>
// A class with general conversion definitions
// </summary>
 
// <use visibility=export>
 
// <reviewed reviewer="Friso Olnon" date="1996/11/06" tests="tConversion" demos="">
// </reviewed>
 
// <synopsis>
// This class contains the general definitions for the Conversion classes.
// <ul>
// <li>
// It defines the signature for the functions converting from input
// to output format (e.g. from local to canonical format). There is
// a version where the number of values is given and a version where
// the number of bytes is given. The latter is there to be able to use
// memcpy as a conversion function (which will often be the case).
// Note that the signatures only differ in return value.
// <li>
// It defines functions to convert Bools to bits and vice-versa.
// These are used elsewhere to store Bools as space efficient as possible.
// Note that these functions are machine independent (they work on little
// and big endian machines).
// <li>
// It defines a private version of memcpy for compilers having a
// different signature for memcpy (e.g. ObjectCenter and DEC-Alpha).
// </ul>
// Static functions in the classes
// <linkto class=CanonicalConversion>CanonicalConversion</linkto>,
// <linkto class=VAXConversion>VAXConversion</linkto>, and
// <linkto class=IBMConversion>IBMConversion</linkto> convert data
// from/to canonical, VAX, and IBM/360 format, resp..
// <br>Classes derived from
// <linkto class=DataConversion>DataConversion</linkto>
// provide the same functionality in a polymorphic way.
// </synopsis>
 
// <motivation>
// This provides a common place for definitions used elsewhere.
// It also provides a uniform interface to memcpy.
// </motivation>
 
// # <todo asof="$DATE$">
// # </todo>
 
class Conversion {
 public:
  // Define the signature of a function converting <src>nvalues</src>
  // values from internal to external format or vice-versa.
  // These functions are used in the <linkto class=TypeIO>IO framework
  // </linkto>, but are also used in the table system.
  // Examples of such conversions are:
  // <br>- local <-> canonical    (when storing in canonical format)
  // <br>- local <-> local        (when storing in local format)
  // <br>- binary <-> ASCII
  // <br>It returns the number of bytes in <em>external</em> format.
  // (For example the ToLocal/FromLocal functions in class
  // <linkto class=CanonicalConversion>CanonicalConversion</linkto>
  // return the number of bytes in canonical format).
  typedef size_t ValueFunction(void* to, const void* from, size_t nvalues);
 
  // Define the signature of a function converting from one
  // format to another providing the number of bytes.
  // It returns the <src>to</src> pointer (similar to memcpy).
  // (For example the byteTo/FromLocalXXX functions in class
  // <linkto class=CanonicalConversion>CanonicalConversion</linkto>.
  typedef void* ByteFunction(void* to, const void* from, size_t nbytes);
 
  // Convert a stream of Bools to output format (as bits).
  // The variable <src>startBit</src> (0-relative) indicates
  // where to start in the <src>to</src> buffer.
  // <group>
  static size_t boolToBit(void* to, const void* from, size_t nvalues);
  static void boolToBit(void* to, const void* from, size_t startBit, size_t nvalues);
  // </group>
 
  // Convert a stream of Bools to output format (as bits).
  // The variable <src>startBit</src> (0-relative) indicates
  // where to start in the <src>from</src> buffer.
  // <group>
  static size_t bitToBool(void* to, const void* from, size_t nvalues);
  static void bitToBool(void* to, const void* from, size_t startBit, size_t nvalues);
  // </group>
 
  // Copy a value using memcpy.
  // It differs from memcpy in the return value.
  // <note> This version has the <src>ValueFunction</src> signature,
  // but it expects as input the number of bytes.
  // </note>
  static size_t valueCopy(void* to, const void* from, size_t nbytes);
 
  // Get a pointer to the memcpy function.
  static ByteFunction* getmemcpy();
 
 private:
  // Copy bits to Bool in an unoptimized way needed when 'to' is not
  // aligned properly.
  static size_t bitToBool_(void* to, const void* from, size_t nvalues);
};
 
inline Conversion::ByteFunction* Conversion::getmemcpy() { return memcpy; }
 
}  // namespace casacore
 
#endif