Package 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:
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.

  • Constructor Details

    • Strided1DWritableBuffer

      public Strided1DWritableBuffer(int flags, BufferProtocol obj, byte[] storage, int index0, int count, int stride) throws ArrayIndexOutOfBoundsException, 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:
      NullPointerException - if storage is null
      ArrayIndexOutOfBoundsException - if index0, count and stride are inconsistent with storage.length
      PyException - BufferError when expectations do not correspond with the type

  • Method Details

    • 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