org.python.core.buffer

Class ZeroByteBuffer

java.lang.Object

org.python.core.buffer.BaseBuffer

org.python.core.buffer.Base1DBuffer

org.python.core.buffer.BaseArrayBuffer

org.python.core.buffer.ZeroByteBuffer

All Implemented Interfaces:

AutoCloseable, BufferProtocol, PyBUF, PyBuffer

public class ZeroByteBuffer
extends BaseArrayBuffer

Buffer API over a zero length, one-dimensional array of one-byte items. The buffer is nominally writable, but since there is nowhere to write to, any attempt to write or read throws an IndexOutOfBoundsException. This class exists mostly to represent zero-length arrays, and particularly, zero-length slices for which implementations of PyBuffer.getBufferSlice(int, int, int, int) in any case need special logic. Bulk operations like copyTo(byte[], int)) and toString() efficiently do nothing, instead of calling complicated logic that finally does nothing.

Nested Class Summary

Nested classes/interfaces inherited from interface org.python.core.PyBuffer

PyBuffer.Pointer

Field Summary

Fields inherited from interface org.python.core.PyBUF

ANY_CONTIGUOUS, AS_ARRAY, C_CONTIGUOUS, CONTIG, CONTIG_RO, CONTIGUITY, F_CONTIGUOUS, FORMAT, FULL, FULL_RO, INDIRECT, IS_C_CONTIGUOUS, IS_F_CONTIGUOUS, MAX_NDIM, NAVIGATION, ND, RECORDS, RECORDS_RO, SIMPLE, STRIDED, STRIDED_RO, STRIDES, WRITABLE

Constructor Summary

Constructors

Constructor and Description
ZeroByteBuffer(int flags, BufferProtocol obj, boolean readonly, boolean hasArray) Construct an instance of a zero-length buffer, choosing whether it should report itself to be read-only through BaseBuffer.isReadonly() or as having a backing array through BaseBuffer.hasArray().

Method Summary

Modifier and Type	Method and Description
int	byteIndex(int... indices) In a ZeroByteBuffer, if the dimensions are right, the index is out of bounds anyway.
int	byteIndex(int index) In a ZeroByteBuffer, the index is always out of bounds.
void	copyFrom(byte[] src, int srcPos, int destIndex, int count) In a ZeroByteBuffer, there is no room for anything, so this throws unless the source count is zero.
void	copyFrom(PyBuffer src) In a ZeroByteBuffer, there is no room for anything, so this throws unless the source count is zero.
void	copyTo(byte[] dest, int destPos) Copy the contents of the buffer to the destination byte array.
void	copyTo(int srcIndex, byte[] dest, int destPos, int count) Copy a simple slice of the buffer-view to the destination byte array, defined by a starting item-index in the source buffer and the count of items to copy.
PyBuffer.Pointer	getBuf() Return a structure describing the slice of a byte array that holds the data being exported to the consumer.
PyBuffer	getBufferSlice(int flags, int start, int count) Only a zero-length slice at zero is valid (in which case, the present buffer will do nicely as a result, with the export count incremented.
PyBuffer	getBufferSlice(int flags, int start, int count, int stride) Only a zero-length slice at zero is valid (in which case, the present buffer will do nicely as a result, with the export count incremented.
int	getLen() The total number of bytes represented by the view, which will be the product of the elements of the shape array, and the item size in bytes.
String	toString() For a ZeroByteBuffer, it's the empty string.

Methods inherited from class org.python.core.buffer.Base1DBuffer

isContiguous

Methods inherited from class org.python.core.buffer.BaseBuffer

byteAt, byteAt, close, getBuffer, getBufferAgain, getFormat, getItemsize, getNdim, getNIOByteBuffer, getObj, getPointer, getPointer, getShape, getStrides, getSuboffsets, hasArray, intAt, intAt, isReadonly, isReleased, release, storeAt, storeAt

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

ZeroByteBuffer

public ZeroByteBuffer(int flags,
                      BufferProtocol obj,
                      boolean readonly,
                      boolean hasArray)
               throws PyException

Construct an instance of a zero-length buffer, choosing whether it should report itself to be read-only through BaseBuffer.isReadonly() or as having a backing array through BaseBuffer.hasArray(). These properties are moot, as any attempt to write to the pretended backing array produces an IndexOutOfBoundsException, but it is less surprising for client code that may ask, if the results are customary for the exporting object.

Parameters:

flags - consumer requirements

obj - exporting object (or null)

readonly - set true if not to be considered writable

hasArray - set true if to be considered as backed by an array

Throws:

PyException - (BufferError) when client expectations do not correspond with the type

Method Detail

getLen

public int getLen()

Description copied from interface: PyBUF

The total number of bytes represented by the view, which will be the product of the elements of the shape array, and the item size in bytes.

Specified by:

getLen in interface PyBUF

Overrides:

getLen in class Base1DBuffer

Returns:

the total number of bytes represented.

byteIndex

public int byteIndex(int index)
              throws IndexOutOfBoundsException

In a ZeroByteBuffer, the index is always out of bounds.

Specified by:

byteIndex in interface PyBuffer

Overrides:

byteIndex in class BaseBuffer

Parameters:

index - item-index from consumer

Returns:

corresponding byte-index in actual storage

Throws:

IndexOutOfBoundsException

byteIndex

public int byteIndex(int... indices)
              throws IndexOutOfBoundsException

In a ZeroByteBuffer, if the dimensions are right, the index is out of bounds anyway.

Specified by:

byteIndex in interface PyBuffer

Overrides:

byteIndex in class BaseArrayBuffer

Parameters:

indices - n-dimensional item-index from consumer

Returns:

corresponding byte-index in actual storage

Throws:

IndexOutOfBoundsException

copyTo

public void copyTo(byte[] dest,
                   int destPos)
            throws IndexOutOfBoundsException

Copy the contents of the buffer to the destination byte array. The number of bytes will be that returned by PyBUF.getLen(), and the order is the storage order in the exporter. (Note: Correct ordering for multidimensional arrays, including those with indirection needs further study.)

The default implementation in BaseBuffer deals with the general one-dimensional case of arbitrary item size and stride.

In a ZeroByteBuffer, there is simply nothing to copy.

Specified by:

copyTo in interface PyBuffer

Overrides:

copyTo in class BaseBuffer

Parameters:

dest - destination byte array

destPos - byte-index in the destination array of the byte [0]

Throws:

IndexOutOfBoundsException - if the destination cannot hold it

copyTo

public void copyTo(int srcIndex,
                   byte[] dest,
                   int destPos,
                   int count)
            throws IndexOutOfBoundsException,
                   PyException

Copy a simple slice of the buffer-view to the destination byte array, defined by a starting item-index in the source buffer and the count of items to copy. This may validly be done only for a one-dimensional buffer, as the meaning of the starting item-index is otherwise not defined. count*itemsize bytes will be occupied in the destination.

The default implementation in BaseBuffer deals with the general one-dimensional case of arbitrary item size and stride, but is unable to optimise access to sequential bytes.

The implementation in BaseArrayBuffer deals with the general one-dimensional case of arbitrary item size and stride.

In a ZeroByteBuffer, there is simply nothing to copy.

Specified by:

copyTo in interface PyBuffer

Overrides:

copyTo in class BaseArrayBuffer

Parameters:

srcIndex - starting item-index in the source buffer

dest - destination byte array

destPos - byte-index in the destination array of the source item [0,...]

count - number of items to copy

Throws:

IndexOutOfBoundsException - if access out of bounds in source or destination

PyException

copyFrom

public void copyFrom(byte[] src,
                     int srcPos,
                     int destIndex,
                     int count)
              throws IndexOutOfBoundsException,
                     PyException

In a ZeroByteBuffer, there is no room for anything, so this throws unless the source count is zero.

Specified by:

copyFrom in interface PyBuffer

Overrides:

copyFrom in class BaseArrayBuffer

Parameters:

src - source byte array

srcPos - location in source of first byte to copy

destIndex - starting item-index in the destination (i.e. this)

count - number of items to copy in

Throws:

IndexOutOfBoundsException - if access out of bounds in source or destination

PyException - (TypeError) if read-only buffer

copyFrom

public void copyFrom(PyBuffer src)
              throws IndexOutOfBoundsException,
                     PyException

In a ZeroByteBuffer, there is no room for anything, so this throws unless the source count is zero.

Specified by:

copyFrom in interface PyBuffer

Overrides:

copyFrom in class BaseArrayBuffer

Parameters:

src - source buffer

Throws:

IndexOutOfBoundsException - if access out of bounds in source or destination

PyException - (TypeError) if read-only buffer

getBufferSlice

public PyBuffer getBufferSlice(int flags,
                               int start,
                               int count)

Only a zero-length slice at zero is valid (in which case, the present buffer will do nicely as a result, with the export count incremented.

Specified by:

getBufferSlice in interface PyBuffer

Overrides:

getBufferSlice in class BaseBuffer

Parameters:

flags - specifying features demanded and the navigational capabilities of the consumer

start - index in the current buffer

count - number of items in the required slice

Returns:

a buffer representing the slice

getBufferSlice

public PyBuffer getBufferSlice(int flags,
                               int start,
                               int count,
                               int stride)

Only a zero-length slice at zero is valid (in which case, the present buffer will do nicely as a result, with the export count incremented.

Parameters:

flags - specifying features demanded and the navigational capabilities of the consumer

start - index in the current buffer

count - number of items in the required slice

stride - index-distance in the current buffer between consecutive items in the slice

Returns:

a buffer representing the slice

getBuf

public PyBuffer.Pointer getBuf()

Return a structure describing the slice of a byte array that holds the data being exported to the consumer. For a one-dimensional contiguous buffer, assuming the following client code where obj has type BufferProtocol:

 PyBuffer a = obj.getBuffer(PyBUF.SIMPLE);
 int itemsize = a.getItemsize();
 PyBuffer.Pointer b = a.getBuf();
 

the item with index k is in the array b.storage at index [b.offset + k*itemsize] to [b.offset + (k+1)*itemsize - 1] inclusive. And if itemsize==1, the item is simply the byte b.storage[b.offset + k]

If the buffer is multidimensional or non-contiguous, storage[offset] is still the (first byte of) the item at index [0] or [0,...,0]. However, it is necessary to navigate b.storage using the shape, strides and maybe suboffsets provided by the API.

BaseArrayBuffer provides a reference to the storage array even when the buffer is intended not to be writable. There can be no enforcement of read-only character once a reference to the byte array has been handed out.

The implementation in ZeroByteBuffer efficiently returns an empty buffer.

Specified by:

getBuf in interface PyBuffer

Overrides:

getBuf in class BaseArrayBuffer

Returns:

structure defining the byte[] slice that is the shared data

toString

public String toString()

For a ZeroByteBuffer, it's the empty string.

Specified by:

toString in interface PyBuffer

Overrides:

toString in class BaseBuffer