org.python.core.buffer

## Class Strided1DWritableBuffer

- java.lang.Object
- - org.python.core.buffer.BaseBuffer
  - - org.python.core.buffer.Base1DBuffer
    - - org.python.core.buffer.BaseArrayBuffer
      - - org.python.core.buffer.Strided1DBuffer
        - - org.python.core.buffer.Strided1DWritableBuffer

All Implemented Interfaces:
  java.lang.AutoCloseable, BufferProtocol, PyBUF, PyBuffer

    public class Strided1DWritableBuffer
    extends Strided1DBuffer

Read-write buffer API over a one-dimensional array of one-byte items, that are evenly-spaced in a storage array. The storage conventions are described in `Strided1DBuffer` of which this is an extension providing write operations and a writable slice.

### 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
`Strided1DWritableBuffer(int flags, BufferProtocol obj, byte[] storage, int index0, int count, int stride)` Provide an instance of `Strided1DWritableBuffer` on a particular array of bytes specifying a starting index, the number of items in the result, and a byte-indexing stride.

### Method Summary

All Methods Instance Methods Concrete Methods
`PyBuffer` `getBufferSlice(int flags, int start, int count, int stride)` Get a `PyBuffer` 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.
`boolean` `isReadonly()` Determine whether the consumer is entitled to write to the exported storage.

### Methods inherited from class org.python.core.buffer.Strided1DBuffer

`byteIndex, getPointer, getPointer`

### 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`

### Methods inherited from class java.lang.Object

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

### Constructor Detail

#### Strided1DWritableBuffer

    public Strided1DWritableBuffer(int flags,
                                   BufferProtocol obj,
                                   byte[] storage,
                                   int index0,
                                   int count,
                                   int stride)
                            throws java.lang.ArrayIndexOutOfBoundsException,
                                   java.lang.NullPointerException,
                                   PyException

Provide an instance of `Strided1DWritableBuffer` on a particular array of bytes specifying a starting index, the number of items in the result, and a byte-indexing stride. The result of `byteAt(i)` will be equal to `storage[index0+stride*i]` (whatever the sign of `stride`), valid for 0≤`i`<`count`.

The constructed `PyBuffer` meets the consumer's expectations as expressed in the `flags` 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 the `storage` array, the lowest and highest index, is not explicitly passed, but is implicit in `index0`, `count` and `stride`. The caller is responsible for checking these fall within the array, or the sub-range the caller is allowed to use.

Parameters:
  `flags` - consumer requirements
  `obj` - exporting object (or `null`)
  `storage` - raw byte array containing exported data
  `index0` - index into storage of item[0]
  `count` - number of items in the slice
  `stride` - byte-index distance from one element to the next in the new PyBuffer
Throws:
  `java.lang.NullPointerException` - if `storage` is null
  `java.lang.ArrayIndexOutOfBoundsException` - if `index0`, `count` and `stride` are inconsistent with `storage.length`
  `PyException` - `BufferError` when expectations do not correspond with the type

### Method Detail

#### isReadonly

    public final boolean isReadonly()

Determine whether the consumer is entitled to write to the exported storage.

Declared `final` returning `true` in `Strided1DWritableBuffer` to make checks unnecessary.

Specified by:
  `isReadonly` in interface `PyBUF`
Overrides:
  `isReadonly` in class `Strided1DBuffer`
Returns:
  true if writing is not allowed, false if it is.

#### getBufferSlice

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

Get a `PyBuffer` 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 a `PyBuffer` with `getBufferSlice` must release it with `PyBuffer.release()` just as if it had been obtained with `PyBuffer.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 by `this.getPointer(i)`. A request for a slice where `start` = s, `count` = N and `stride` = 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` and `stride` will be translated from the arguments given, through this buffer's stride and item size. The caller always expresses `start` and `strides` 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 composite `index0` is r+sp and the composite `stride` is mp.

`Strided1DWritableBuffer` provides an implementation that returns a writable slice.

Specified by:
  `getBufferSlice` in interface `PyBuffer`
Overrides:
  `getBufferSlice` in class `Strided1DBuffer`
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