nil: Move Z slice offset calculations to a helper

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/28103>

src/nouveau/nil/nil_image.c

@@ -702,6 +702,34 @@ nil_image_init(struct nv_device_info *dev,
    return true;
 }
 
+/** Offset of the given Z slice within the level */
+uint64_t
+nil_image_level_z_offset_B(const struct nil_image *image,
+                           uint32_t level, uint32_t z)
+{
+   assert(level < image->num_levels);
+   const struct nil_extent4d lvl_extent_px =
+      nil_image_level_extent_px(image, level);
+   assert(z < lvl_extent_px.d);
+
+   const struct nil_tiling *lvl_tiling = &image->levels[level].tiling;
+
+   const uint32_t z_tl = z >> lvl_tiling->z_log2;
+   const uint32_t z_GOB = z & BITFIELD_MASK(lvl_tiling->z_log2);
+
+   const struct nil_extent4d lvl_extent_tl =
+      nil_extent4d_px_to_tl(lvl_extent_px, *lvl_tiling,
+                            image->format, image->sample_layout);
+   uint64_t offset_B = lvl_extent_tl.w * lvl_extent_tl.h * (uint64_t)z_tl *
+                       nil_tiling_size_B(*lvl_tiling);
+
+   const struct nil_extent4d tiling_extent_B =
+      nil_tiling_extent_B(*lvl_tiling);
+   offset_B += tiling_extent_B.w * tiling_extent_B.h * z_GOB;
+
+   return offset_B;
+}
+
 uint64_t
 nil_image_level_depth_stride_B(const struct nil_image *image, uint32_t level)
 {

src/nouveau/nil/nil_image.h

@@ -220,6 +220,9 @@ nil_image_level_layer_offset_B(const struct nil_image *image,
    return image->levels[level].offset_B + (layer * image->array_stride_B);
 }
 
+uint64_t nil_image_level_z_offset_B(const struct nil_image *image,
+                                    uint32_t level, uint32_t z);
+
 static inline uint32_t
 nil_image_mip_tail_offset_B(const struct nil_image *image)
 {

src/nouveau/nil/nil_image_tic.c

@@ -415,29 +415,10 @@ nvb097_nil_image_fill_tic(const struct nil_image *image,
    /* There's no base layer field in the texture header */
    uint64_t layer_address = base_address;
    if (view->type == NIL_VIEW_TYPE_3D_SLICED) {
-      assert(view->num_levels == 1);
+      assert(image->num_levels == 1);
       assert(view->base_array_layer + view->array_len <= image->extent_px.d);
-
-      /* For sliced 3D images, computing the offset is a bit more complicated.
-       * We first have to compute the offset to the tile then, within that
-       * tile, the offset to the GOB.
-       *
-       * TODO: If we ever enable 3D gobs, we'll also have to compute the
-       * offset within the gob.
-       */
-      const uint32_t z_tl = view->base_array_layer >> tiling->z_log2;
-      const uint32_t z_GOB =
-         view->base_array_layer & BITFIELD_MASK(tiling->z_log2);
-
-      const struct nil_extent4d extent_tl =
-         nil_extent4d_px_to_tl(image->extent_px, *tiling,
-                               image->format, image->sample_layout);
-      layer_address += extent_tl.w * extent_tl.h * z_tl *
-                       nil_tiling_size_B(*tiling);
-
-      const struct nil_extent4d tiling_extent_B =
-         nil_tiling_extent_B(*tiling);
-      layer_address += tiling_extent_B.w * tiling_extent_B.h * z_GOB;
+      layer_address += nil_image_level_z_offset_B(image, view->base_level,
+                                                  view->base_array_layer);
    } else {
       assert(view->base_array_layer + view->array_len <= image->extent_px.a);
       layer_address += view->base_array_layer * image->array_stride_B;