Class Strided1DBuffer
- All Implemented Interfaces:
AutoCloseable
,BufferProtocol
,PyBUF
,PyBuffer
- Direct Known Subclasses:
Strided1DWritableBuffer
storage
, index0
and count
properties in the usual way, designating a slice (or all) of a byte array, but also a
stride
property (equal to getStrides()[0]
).
Let the underlying buffer be the byte array u(i) for i=0..N-1, let x be the
Strided1DBuffer
, and let the stride be p. The storage works as follows.
Designate by x(j), for j=0..L-1, the byte at index j, that is, the byte
retrieved by x.byteAt(j)
. Thus, we store x(j) at u(a+pj), that is,
x(0) = u(a). When we construct such a buffer, we have to supply a =
index0
, L = count
, and p = stride
as the
constructor arguments. The last item in the slice x(L-1) is stored at u(a+p(L-1)).
For the simple case of positive stride, constructor argument index0
is the low index
of the range occupied by the data. When the stride is negative, that is to say p<0, and
L>1, this will be to the left of u(a), and the constructor argument
index0
is not then the low index of the range occupied by the data. Clearly both
these indexes must be in the range 0 to N-1 inclusive, a rule enforced by the constructors
(unless L=0, when it is assumed no array access will take place).
The class may be used by exporters to create a strided slice (e.g. to export the diagonal of a
matrix) and in particular by other buffers to create strided slices of themselves, such as to
create the memoryview
that is returned as an extended slice of a
memoryview
.
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Nested Class Summary
Nested classes/interfaces inherited from interface org.python.core.PyBuffer
PyBuffer.Pointer
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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
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Constructor Summary
ConstructorDescriptionStrided1DBuffer
(int flags, BufferProtocol obj, byte[] storage, int index0, int count, int stride) Provide an instance ofStrided1DBuffer
on a particular array of bytes specifying a starting index, the number of items in the result, and a byte-indexing stride. -
Method Summary
Modifier and TypeMethodDescriptionfinal int
byteIndex
(int index) Convert an item index (for a one-dimensional buffer) to an absolute byte index in the storage shared by the exporter.getBufferSlice
(int flags, int start, int count, int stride) Get aPyBuffer
that represents a slice of the current one described in terms of a start index, number of items to include in the slice, and the stride in the current buffer.getPointer
(int index) Return a structure describing the position in a byte array of a single item from the data being exported to the consumer.getPointer
(int... indices) Return a structure describing the position in a byte array of a single item from the data being exported to the consumer, in the case that array may be multi-dimensional.boolean
Determine whether the consumer is entitled to write to the exported storage.Methods inherited from class org.python.core.buffer.BaseArrayBuffer
byteIndex, copyFrom, copyFrom, copyTo, getBuf
Methods inherited from class org.python.core.buffer.Base1DBuffer
getLen, isContiguous
Methods inherited from class org.python.core.buffer.BaseBuffer
byteAt, byteAt, close, copyTo, getBuffer, getBufferAgain, getBufferSlice, getFormat, getItemsize, getNdim, getNIOByteBuffer, getObj, getShape, getStrides, getSuboffsets, hasArray, intAt, intAt, isReleased, release, storeAt, storeAt, toString
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Constructor Details
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Strided1DBuffer
public Strided1DBuffer(int flags, BufferProtocol obj, byte[] storage, int index0, int count, int stride) throws ArrayIndexOutOfBoundsException, NullPointerException, PyException Provide an instance ofStrided1DBuffer
on a particular array of bytes specifying a starting index, the number of items in the result, and a byte-indexing stride. The result ofbyteAt(i)
will be equal tostorage[index0+stride*i]
(whatever the sign ofstride
), valid for0<=i<count
. The constructor checks that all these indices lie within thestorage
array (unlesscount=0
).The constructed
PyBuffer
meets the consumer's expectations as expressed in theflags
argument, or an exception will be thrown if these are incompatible with the type (e.g. the consumer does not specify that it understands the strides array). Note that the actual range in thestorage
array, the lowest and highest index, is not explicitly passed, but is implicit inindex0
,count
andstride
. The constructor checks that these indices lie within thestorage
array (unlesscount=0
).- Parameters:
flags
- consumer requirementsobj
- exporting object (ornull
)storage
- raw byte array containing exported dataindex0
- index into storage of item[0]count
- number of items in the slicestride
- byte-index distance from one element to the next in the new PyBuffer- Throws:
NullPointerException
- ifstorage
is nullArrayIndexOutOfBoundsException
- ifindex0
,count
andstride
are inconsistent withstorage.length
PyException
-BufferError
when expectations do not correspond with the type
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Method Details
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isReadonly
public boolean isReadonly()Description copied from interface:PyBUF
Determine whether the consumer is entitled to write to the exported storage.- Specified by:
isReadonly
in interfacePyBUF
- Overrides:
isReadonly
in classBaseBuffer
- Returns:
- true if writing is not allowed, false if it is.
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byteIndex
Description copied from interface:PyBuffer
Convert an item index (for a one-dimensional buffer) to an absolute byte index in the storage shared by the exporter. The storage exported as aPyBuffer
is a linearly-indexed sequence of bytes, although it may not actually be a heap-allocated Javabyte[]
object. The purpose of this method is to allow the exporter to define the relationship between the item index (as used inPyBuffer.byteAt(int)
) and the byte-index (as used with theByteBuffer
returned byPyBuffer.getNIOByteBuffer()
). SeePyBuffer.byteIndex(int[])
for discussion of the multi-dimensional case.- Specified by:
byteIndex
in interfacePyBuffer
- Overrides:
byteIndex
in classBaseBuffer
- Parameters:
index
- item-index from consumer- Returns:
- corresponding byte-index in actual storage
- Throws:
IndexOutOfBoundsException
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getBufferSlice
Get aPyBuffer
that represents a slice of the current one described in terms of a start index, number of items to include in the slice, and the stride in the current buffer. A consumer that obtains aPyBuffer
withgetBufferSlice
must release it withPyBuffer.release()
just as if it had been obtained withPyBuffer.getBuffer(int)
Suppose that x(i) denotes the ith element of the current buffer, that is, the byte retrieved by
this.byteAt(i)
or the unit indicated bythis.getPointer(i)
. A request for a slice wherestart
= s,count
= N andstride
= m, results in a buffer y such that y(k) = x(s+km) where k=0..(N-1). In Python terms, this is the slice x[s : s+(N-1)m+1 : m] (if m>0) or the slice x[s : s+(N-1)m-1 : m] (if m<0). Implementations should check that this range is entirely within the current buffer.In a simple buffer backed by a contiguous byte array, the result is a strided PyBuffer on the same storage but where the offset is adjusted by s and the stride is as supplied. If the current buffer is already strided and/or has an item size larger than single bytes, the new
start
index,count
andstride
will be translated from the arguments given, through this buffer's stride and item size. The caller always expressesstart
andstrides
in terms of the abstract view of this buffer.Strided1DBuffer
provides an implementation for slicing already-strided bytes in one dimension. In that case, x(i) = u(r+ip) for i = 0..L-1 where u is the underlying buffer, and r, p and L are the start, stride and count with which x was created from u. Thus y(k) = u(r+sp+kmp), that is, the compositeindex0
is r+sp and the compositestride
is mp.- Parameters:
flags
- specifying features demanded and the navigational capabilities of the consumerstart
- index in the current buffercount
- number of items in the required slicestride
- index-distance in the current buffer between consecutive items in the slice- Returns:
- a buffer representing the slice
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getPointer
Description copied from interface:PyBuffer
Return a structure describing the position in a byte array of a single item from the data being exported to the consumer. For a one-dimensional contiguous buffer, assuming the following client code whereobj
has typeBufferProtocol
:int k = ... ; PyBuffer a = obj.getBuffer(PyBUF.FULL); int itemsize = a.getItemsize(); PyBuffer.Pointer b = a.getPointer(k);
the item with indexk
is in the arrayb.storage
at index[b.offset]
to[b.offset + itemsize - 1]
inclusive. And ifitemsize==1
, the item is simply the byteb.storage[b.offset]
Essentially this is a method for computing the offset of a particular index. The client is free to navigate the underlying buffer
b.storage
without respecting these boundaries.- Specified by:
getPointer
in interfacePyBuffer
- Overrides:
getPointer
in classBaseBuffer
- Parameters:
index
- in the buffer to position the pointer- Returns:
- structure defining the byte[] slice that is the shared data
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getPointer
Description copied from interface:PyBuffer
Return a structure describing the position in a byte array of a single item from the data being exported to the consumer, in the case that array may be multi-dimensional. For a 3-dimensional contiguous buffer, assuming the following client code whereobj
has typeBufferProtocol
:int i, j, k; // ... calculation that assigns i, j, k PyBuffer a = obj.getBuffer(PyBUF.FULL); int itemsize = a.getItemsize(); PyBuffer.Pointer b = a.getPointer(i,j,k);
the item with index[i,j,k]
is in the arrayb.storage
at index[b.offset]
to[b.offset + itemsize - 1]
inclusive. And ifitemsize==1
, the item is simply the byteb.storage[b.offset]
Essentially this is a method for computing the offset of a particular index. The client is free to navigate the underlying buffer
b.storage
without respecting these boundaries. If the buffer is non-contiguous, the above description is still valid (since a multi-byte item must itself be contiguously stored), but in any additional navigation ofb.storage[]
to other items, the client must use the shape, strides and sub-offsets provided by the API. Normally one startsb = a.getBuf()
in order to establish the offset of index [0,...,0].- Specified by:
getPointer
in interfacePyBuffer
- Overrides:
getPointer
in classBaseBuffer
- Parameters:
indices
- multidimensional index at which to position the pointer- Returns:
- structure defining the byte[] slice that is the shared data
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