[gegl] buffer: add optimized 6-byte case to gegl_buffer_iterate_write()

[N/A <ell src gnome org>]

commit 3aeda3e1df7e095e8e08e42ac784b85f8b09cbce
Author: Ell <ell_se yahoo com>
Date:   Wed Mar 14 05:44:52 2018 -0400

    buffer: add optimized 6-byte case to gegl_buffer_iterate_write()
    
    ... to match the set of optimized gegl_buffer_iterate_read_simple()
    cases.

 gegl/buffer/gegl-buffer-access.c |   20 ++++++++++++++++++++
 1 files changed, 20 insertions(+), 0 deletions(-)
---
diff --git a/gegl/buffer/gegl-buffer-access.c b/gegl/buffer/gegl-buffer-access.c
index d33d06a..a225ba7 100644
--- a/gegl/buffer/gegl-buffer-access.c
+++ b/gegl/buffer/gegl-buffer-access.c
@@ -580,6 +580,26 @@ with multi-threading - and should be added back later.
                       bp += buf_stride;
                     }
                     break;
+                  case 6:
+                    CHECK_ALIGNMENT (uint16_t);
+                    for (row = offsety;
+                         row < tile_height && y < height;
+                         row++, y++)
+                    {
+                      if (buffer_y + y >= buffer_abyss_y &&
+                          buffer_y + y < abyss_y_total)
+                        {
+                          ((uint16_t*)(&tp[lskip_offset]))[0] =
+                          ((uint16_t*)(&bp[lskip_offset]))[0];
+                          ((uint16_t*)(&tp[lskip_offset]))[1] =
+                          ((uint16_t*)(&bp[lskip_offset]))[1];
+                          ((uint16_t*)(&tp[lskip_offset]))[2] =
+                          ((uint16_t*)(&bp[lskip_offset]))[2];
+                        }
+                      tp += tile_stride;
+                      bp += buf_stride;
+                    }
+                    break;
                   case 8:
                     CHECK_ALIGNMENT (uint64_t);
                     for (row = offsety;