api/appendix_d.asciidoc

// Copyright 2017-2020 The Khronos Group. This work is licensed under a
// Creative Commons Attribution 4.0 International License; see
// http://creativecommons.org/licenses/by/4.0/

[appendix]
[[check-copy-overlap]]
= Checking for Memory Copy Overlap

The following code describes how to determine if there is overlap between
the source and destination rectangles specified to {clEnqueueCopyBufferRect}
provided the source and destination buffers refer to the same buffer object.

[source,c]
----
unsigned int
check_copy_overlap(const size_t src_origin[],
                   const size_t dst_origin[],
                   const size_t region[],
                   const size_t row_pitch,
                   const size_t slice_pitch )
{
  const size_t slice_size = (region[1] - 1) * row_pitch + region[0];
  const size_t block_size = (region[2] - 1) * slice_pitch + slice_size;
  const size_t src_start = src_origin[2] * slice_pitch
                           + src_origin[1] * row_pitch
                           + src_origin[0];
  const size_t src_end = src_start + block_size;
  const size_t dst_start = dst_origin[2] * slice_pitch
                           + dst_origin[1] * row_pitch
                           + dst_origin[0];
  const size_t dst_end = dst_start + block_size;

  /* No overlap if dst ends before src starts or if src ends
   * before dst starts.
   */
  if( (dst_end <= src_start) || (src_end <= dst_start) ){
    return 0;
  }

  /* No overlap if region[0] for dst or src fits in the gap
   * between region[0] and row_pitch.
   */
  {
    const size_t src_dx = src_origin[0] % row_pitch;
    const size_t dst_dx = dst_origin[0] % row_pitch;

    if( ((dst_dx >= src_dx + region[0]) &&
        (dst_dx + region[0] <= src_dx + row_pitch)) ||
        ((src_dx >= dst_dx + region[0]) &&
        (src_dx + region[0] <= dst_dx + row_pitch)) )
      {
        return 0;
      }
  }

  /* No overlap if region[1] for dst or src fits in the gap
   * between region[1] and slice_pitch.
   */
   {
      const size_t src_dy =
        (src_origin[1] * row_pitch + src_origin[0]) % slice_pitch;
      const size_t dst_dy =
        (dst_origin[1] * row_pitch + dst_origin[0]) % slice_pitch;

      if( ((dst_dy >= src_dy + slice_size) &&
          (dst_dy + slice_size <= src_dy + slice_pitch)) ||
          ((src_dy >= dst_dy + slice_size) &&
          (src_dy + slice_size <= dst_dy + slice_pitch)) ) {
        return 0;
      }
   }

 /* Otherwise src and dst overlap. */
 return 1;
}
----