Jorge Leitão created ARROW-14453:
------------------------------------
Summary: [C data interface] Clarify that buffers must only be
accessed past the offset
Key: ARROW-14453
URL: https://issues.apache.org/jira/browse/ARROW-14453
Project: Apache Arrow
Issue Type: Improvement
Reporter: Jorge Leitão
I would like to propose that we clarify in the c data interface that the
buffers can only be accessed past the offset (with the pointer arithmetic
corresponding to the buffer).
E.g. given a primitive array with an offset of 10 and buffer starting at
pointer position `p`, consumers _must not_ access any of the positions [p, p+1,
..., p-1+9].
Without the condition above, it is not possible for a user to use a sliced
buffer on a primitive array with a validity and an offset.
E.g. consider an array with an offset of 10, a buffer of 12 u8s that has been
sliced by 4. For the array to be exported correctly, we will need to offset the
buffer by -6 (4 - 10), so that the consumer can jump the first 10 bytes and
only "see" the bytes at positions 4, 5, 6, etc of the original pointer.
Note that this behavior (of slicing a buffer and building an array with it) can
only be done with buffers. In the booleanArray it is currently not possible to
"slice" the buffer without it being a multiple of 8 slots, since the C data
interface has no mechanism to share independent offsets.
--
This message was sent by Atlassian Jira
(v8.3.4#803005)
