Class Strided1DNIOBuffer
- All Implemented Interfaces:
AutoCloseable
,BufferProtocol
,PyBUF
,PyBuffer
java.nio.ByteBuffer
of one-byte items,
that are evenly-spaced in that store. The buffer has storage
, index0
and length
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 sequence u(i) for i=0..N-1, let x be
the Strided1DNIOBuffer
, 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
ConstructorDescriptionStrided1DNIOBuffer
(int flags, BufferProtocol obj, ByteBuffer storage, int index0, int count, int stride) Provide an instance ofStrided1DNIOBuffer
on a particularByteBuffer
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.Methods inherited from class org.python.core.buffer.BaseNIOBuffer
byteIndex, copyFrom, copyTo, 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, copyFrom, copyTo, getBuffer, getBufferAgain, getBufferSlice, getFormat, getItemsize, getNdim, getNIOByteBuffer, getObj, getPointer, getPointer, getShape, getStrides, getSuboffsets, hasArray, intAt, intAt, isReadonly, isReleased, release, storeAt, storeAt, toString
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Constructor Details
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Strided1DNIOBuffer
public Strided1DNIOBuffer(int flags, BufferProtocol obj, ByteBuffer storage, int index0, int count, int stride) throws ArrayIndexOutOfBoundsException, NullPointerException, PyException Provide an instance ofStrided1DNIOBuffer
on a particularByteBuffer
specifying a starting index, the number of items in the result, and a byte-indexing stride. The result ofbyteAt(i)
will be equal tostorage.get(index0+stride*i)
(whatever the sign ofstride
), valid for0<=i<count
. The constructor checks that all these indices lie within thestorage
(unlesscount=0
). No reference will be kept to theByteBuffer
passed in. (It is duplicated.)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
-ByteBuffer
wrapping exported dataindex0
- index into storage of item[0]count
- number of items in the slicestride
- in between successive elements of 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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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.Strided1DNIOBuffer
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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