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casacore::TileStepper Class Reference

traverse a tiled Lattice optimally with a tile cursor More...

#include <TileStepper.h>

Inheritance diagram for casacore::TileStepper:
casacore::LatticeNavigator

Public Member Functions

 TileStepper (const IPosition &latticeShape, const IPosition &tileShape)
 Construct a TileStepper by specifying the Lattice shape, a tile shape, and an optional axis path (default is natural order). More...
 
 TileStepper (const IPosition &latticeShape, const IPosition &tileShape, const IPosition &axisPath)
 
 TileStepper (const TileStepper &other)
 Copy constructor (copy semantics). More...
 
 ~TileStepper ()
 
TileStepperoperator= (const TileStepper &other)
 Assignment (copy semantics). More...
 
virtual Bool operator++ (int)
 Increment operator (postfix or prefix version) - move the cursor forward one step. More...
 
virtual Bool operator-- (int)
 Decrement operator (postfix or prefix version) - move the cursor backwards one step. More...
 
virtual void reset ()
 Function to move the cursor to the beginning of the Lattice. More...
 
virtual Bool atStart () const
 Function which returns "True" if the cursor is at the beginning of the Lattice, otherwise, returns "False". More...
 
virtual Bool atEnd () const
 Function which returns "True" if an attempt has been made to increment the cursor beyond the end of the Lattice. More...
 
virtual uInt nsteps () const
 Function to return the number of steps (increments & decrements) taken since construction (or since last reset). More...
 
virtual IPosition position () const
 Function which returns the current position of the beginning of the cursor. More...
 
virtual IPosition endPosition () const
 Function which returns the current position of the end of the cursor. More...
 
virtual IPosition latticeShape () const
 Functions which return the shape of the Lattice being iterated through. More...
 
virtual IPosition subLatticeShape () const
 
virtual IPosition cursorShape () const
 Function which returns the shape of the cursor. More...
 
virtual IPosition cursorAxes () const
 Function which returns the axes of the cursor. More...
 
IPosition tileShape () const
 Function which returns the shape of the "tile" the cursor will iterate through before moving onto the next tile. More...
 
virtual Bool hangOver () const
 Function which returns "True" if the increment/decrement operators have moved the cursor position such that part of the cursor beginning or end is hanging over the edge of the Lattice. More...
 
virtual void subSection (const IPosition &blc, const IPosition &trc)
 Functions to specify a "section" of the Lattice to step over. More...
 
virtual void subSection (const IPosition &blc, const IPosition &trc, const IPosition &inc)
 
virtual IPosition blc () const
 Return the bottom left hand corner (blc), top right corner (trc) or step size (increment) used by the current sub-Lattice. More...
 
virtual IPosition trc () const
 
virtual IPosition increment () const
 
virtual const IPositionaxisPath () const
 Return the axis path. More...
 
virtual LatticeNavigatorclone () const
 Function which returns a pointer to dynamic memory of an exact copy of this instance. More...
 
virtual Bool ok () const
 Function which checks the internal data of this class for correct dimensionality and consistant values. More...
 
virtual uInt calcCacheSize (const IPosition &cubeShape, const IPosition &tileShape, uInt maxCacheSize, uInt bucketSize) const
 Calculate the cache size (in tiles) for this type of access to a lattice in the given row of the tiled hypercube. More...
 
- Public Member Functions inherited from casacore::LatticeNavigator
 LatticeNavigator ()
 Default constructor. More...
 
 LatticeNavigator (const LatticeNavigator &)
 Copy constructor. More...
 
LatticeNavigatoroperator= (const LatticeNavigator &)
 Assignment. More...
 
virtual ~LatticeNavigator ()
 A virtual destructor. More...
 
Bool operator++ ()
 
Bool operator-- ()
 
virtual IPosition relativePosition () const
 
virtual IPosition relativeEndPosition () const
 
virtual IPosition hangOverBlc () const
 Functions which return the "bottom left corner" and the "top right corner" of the cursor that does not hangover. More...
 
virtual IPosition hangOverTrc () const
 

Private Member Functions

 TileStepper ()
 Prevent the default constructor from being used. More...
 

Private Attributes

IPosition itsBlc
 
IPosition itsTrc
 
IPosition itsInc
 
LatticeIndexer itsSubSection
 
LatticeIndexer itsTiler
 
IPosition itsTilerCursorPos
 
IPosition itsTileShape
 
IPosition itsAxisPath
 
IPosition itsCurBlc
 
IPosition itsCurTrc
 
uInt itsNsteps
 
Bool itsEnd
 
Bool itsStart
 

Detailed Description

traverse a tiled Lattice optimally with a tile cursor

Intended use:

Public interface

Review Status

Reviewed By:
Peter Barnes
Date Reviewed:
1999/10/30
Test programs:
tTileStepper

Prerequisite

Etymology

TileStepper is used to step optimally through a tiled Lattice.

Synopsis

When you wish to traverse a Lattice (say, a PagedArray or an Image) you will usually create a LatticeIterator. Once created, you may attach a LatticeNavigator to the iterator. A TileStepper is a concrete class derived from the abstract LatticeNavigator that allows you to step through the Lattice in a way that will minimize the amount of cache memory consumed and maximize the speed.

Some Lattices (in particular PagedArrays) are stored (on disk) in tiles. For an N-dimensional Lattice a tile is an N-dimensional subsection with fewer elements along each axis. For example a Lattice of shape [512,512,4,32] may have a tile shape of [32,16,4,16], and there will be 16*32*1*2 (=1024) tiles in the entire Lattice. To allow efficient access of the data in a Lattice some tiles are cached in memory. As each tile may consume a fair bit of memory (in this example 128kBytes, assuming each element consumes 4 bytes), it is desirable to minimise the number of tiles held in the cache. But it is also desirable to minimise the number of times a tiles must be read into or written from the cache as this may require a time consuming operation like disk I/O.

TileStepper steps through a lattice in a tile-by-tile way. This means that the cache contains 1 tile only and that a tile is accessed only once. It should be clear that traversing a lattice in this way cannot be used if an entire vector or plane is needed. It is, however, very well suited for purposes like initialising a lattice, where the order in which the lattice pixels are accessed is not important.

In constructing a TileStepper, you specify the Lattice shape, the tile shape and optionally the axis path. The axis path defines the order in which the tiles are fetched from the lattice. Default is the natural order (thus x-axis in the inner loop).
It is possible to use the function subSection to traverse only a subsection of the lattice.

The cursor position can be incremented or decremented to retrieve the next or previous tile in the Lattice. The position of the next tile in the Lattice will depend on the tile shape, and is described above.
Note that the cursor shape does not need to be constant when iterating through the lattice. If the lattice shape is not an integer multiple of the tile shape, the cursor will be smaller on the edges of the lattice.

Example

This example initializes a lattice with the given value.

void init (Lattice<Complex>& cArray, Complex value)
{
const IPosition latticeShape = cArray.shape();
const IPosition tileShape = cArray.niceCursorShape();
TileStepper tsx(latticeShape, tileShape);
LatticeIterator<Complex> lix(cArray, tsx);
for (lix.reset();!lix.atEnd();lix++)
lix.woCursor() = value;
}
}

Note that a TileStepper is the default navigator for an iterator. So the code above could be made simpler like shown below. Also note that this example is a bit artificial, because the Lattice::set() function should be used to initialize a lattice.

void init (Lattice<Complex>& cArray, Complex value)
{
LatticeIterator<Complex> lix(cArray);
for (lix.reset();!lix.atEnd();lix++)
lix.woCursor() = value;
}
}

Motivation

This class makes it possible to traverse a lattice in the optimal way.

Definition at line 138 of file TileStepper.h.

Constructor & Destructor Documentation

casacore::TileStepper::TileStepper ( const IPosition latticeShape,
const IPosition tileShape 
)

Construct a TileStepper by specifying the Lattice shape, a tile shape, and an optional axis path (default is natural order).

Is is nearly always advisable to make the tileShape identical to the Lattice tileShape. This can be obtained by lat.niceCursorShape() where lat is a Lattice object.

casacore::TileStepper::TileStepper ( const IPosition latticeShape,
const IPosition tileShape,
const IPosition axisPath 
)
casacore::TileStepper::TileStepper ( const TileStepper other)

Copy constructor (copy semantics).

casacore::TileStepper::~TileStepper ( )
casacore::TileStepper::TileStepper ( )
private

Prevent the default constructor from being used.

Member Function Documentation

virtual Bool casacore::TileStepper::atEnd ( ) const
virtual

Function which returns "True" if an attempt has been made to increment the cursor beyond the end of the Lattice.

Implements casacore::LatticeNavigator.

virtual Bool casacore::TileStepper::atStart ( ) const
virtual

Function which returns "True" if the cursor is at the beginning of the Lattice, otherwise, returns "False".

Implements casacore::LatticeNavigator.

virtual const IPosition& casacore::TileStepper::axisPath ( ) const
virtual

Return the axis path.

Implements casacore::LatticeNavigator.

virtual IPosition casacore::TileStepper::blc ( ) const
virtual

Return the bottom left hand corner (blc), top right corner (trc) or step size (increment) used by the current sub-Lattice.

If no sub-Lattice has been defined (with the subSection function) these functions return blc=0, trc=latticeShape-1, increment=1, ie. the entire Lattice.

Reimplemented from casacore::LatticeNavigator.

virtual uInt casacore::TileStepper::calcCacheSize ( const IPosition cubeShape,
const IPosition tileShape,
uInt  maxCacheSize,
uInt  bucketSize 
) const
virtual

Calculate the cache size (in tiles) for this type of access to a lattice in the given row of the tiled hypercube.

Implements casacore::LatticeNavigator.

virtual LatticeNavigator* casacore::TileStepper::clone ( ) const
virtual

Function which returns a pointer to dynamic memory of an exact copy of this instance.

The pointer returned by this function must be deleted externally.

Implements casacore::LatticeNavigator.

virtual IPosition casacore::TileStepper::cursorAxes ( ) const
virtual

Function which returns the axes of the cursor.

Implements casacore::LatticeNavigator.

virtual IPosition casacore::TileStepper::cursorShape ( ) const
virtual

Function which returns the shape of the cursor.

This always includes all axes (i.e. it includes degenerates axes)

Implements casacore::LatticeNavigator.

virtual IPosition casacore::TileStepper::endPosition ( ) const
virtual

Function which returns the current position of the end of the cursor.

The endPosition function is relative the origin in the main Lattice.

Implements casacore::LatticeNavigator.

virtual Bool casacore::TileStepper::hangOver ( ) const
virtual

Function which returns "True" if the increment/decrement operators have moved the cursor position such that part of the cursor beginning or end is hanging over the edge of the Lattice.

This always returns False.

Implements casacore::LatticeNavigator.

virtual IPosition casacore::TileStepper::increment ( ) const
virtual

Reimplemented from casacore::LatticeNavigator.

virtual IPosition casacore::TileStepper::latticeShape ( ) const
virtual

Functions which return the shape of the Lattice being iterated through.

latticeShape always returns the shape of the main Lattice while subLatticeShape returns the shape of any sub-Lattice defined using the subSection function.

Implements casacore::LatticeNavigator.

virtual uInt casacore::TileStepper::nsteps ( ) const
virtual

Function to return the number of steps (increments & decrements) taken since construction (or since last reset).

This is a running count of all cursor movement (operator++ or operator--), even though N-increments followed by N-decrements will always leave the cursor in the original position.

Implements casacore::LatticeNavigator.

virtual Bool casacore::TileStepper::ok ( ) const
virtual

Function which checks the internal data of this class for correct dimensionality and consistant values.

Returns True if everything is fine otherwise returns False

Reimplemented from casacore::LatticeNavigator.

virtual Bool casacore::TileStepper::operator++ ( int  )
virtual

Increment operator (postfix or prefix version) - move the cursor forward one step.

Returns True if the cursor was moved.

Implements casacore::LatticeNavigator.

virtual Bool casacore::TileStepper::operator-- ( int  )
virtual

Decrement operator (postfix or prefix version) - move the cursor backwards one step.

Returns True if the cursor was moved.

Implements casacore::LatticeNavigator.

TileStepper& casacore::TileStepper::operator= ( const TileStepper other)

Assignment (copy semantics).

virtual IPosition casacore::TileStepper::position ( ) const
virtual

Function which returns the current position of the beginning of the cursor.

The position function is relative to the origin in the main Lattice.

Implements casacore::LatticeNavigator.

virtual void casacore::TileStepper::reset ( )
virtual

Function to move the cursor to the beginning of the Lattice.

Also resets the number of steps (nsteps function) to zero.

Implements casacore::LatticeNavigator.

virtual IPosition casacore::TileStepper::subLatticeShape ( ) const
virtual

Reimplemented from casacore::LatticeNavigator.

virtual void casacore::TileStepper::subSection ( const IPosition blc,
const IPosition trc 
)
virtual

Functions to specify a "section" of the Lattice to step over.

A section is defined in terms of the Bottom Left Corner (blc), Top Right Corner (trc), and step size (inc), on ALL of its axes, including degenerate axes. The step size defaults to one if not specified.

Reimplemented from casacore::LatticeNavigator.

virtual void casacore::TileStepper::subSection ( const IPosition blc,
const IPosition trc,
const IPosition inc 
)
virtual

Reimplemented from casacore::LatticeNavigator.

IPosition casacore::TileStepper::tileShape ( ) const

Function which returns the shape of the "tile" the cursor will iterate through before moving onto the next tile.

virtual IPosition casacore::TileStepper::trc ( ) const
virtual

Reimplemented from casacore::LatticeNavigator.

Member Data Documentation

IPosition casacore::TileStepper::itsAxisPath
private

Definition at line 278 of file TileStepper.h.

IPosition casacore::TileStepper::itsBlc
private

Definition at line 271 of file TileStepper.h.

IPosition casacore::TileStepper::itsCurBlc
private

Definition at line 279 of file TileStepper.h.

IPosition casacore::TileStepper::itsCurTrc
private

Definition at line 280 of file TileStepper.h.

Bool casacore::TileStepper::itsEnd
private

Definition at line 282 of file TileStepper.h.

IPosition casacore::TileStepper::itsInc
private

Definition at line 273 of file TileStepper.h.

uInt casacore::TileStepper::itsNsteps
private

Definition at line 281 of file TileStepper.h.

Bool casacore::TileStepper::itsStart
private

Definition at line 283 of file TileStepper.h.

LatticeIndexer casacore::TileStepper::itsSubSection
private

Definition at line 274 of file TileStepper.h.

LatticeIndexer casacore::TileStepper::itsTiler
private

Definition at line 275 of file TileStepper.h.

IPosition casacore::TileStepper::itsTilerCursorPos
private

Definition at line 276 of file TileStepper.h.

IPosition casacore::TileStepper::itsTileShape
private

Definition at line 277 of file TileStepper.h.

IPosition casacore::TileStepper::itsTrc
private

Definition at line 272 of file TileStepper.h.


The documentation for this class was generated from the following file: