fix dimension order in threads range

src/pystencils/backend/platforms/generic_gpu.py

@@ -13,6 +13,7 @@ from .platform import Platform
 
 
 class GpuThreadsRange:
+    """Number of threads required by a GPU kernel, in order (x, y, z)."""
 
     @staticmethod
     def from_ispace(ispace: IterationSpace) -> GpuThreadsRange:
@@ -41,6 +42,7 @@ class GpuThreadsRange:
 
     @property
     def num_work_items(self) -> tuple[PsExpression, ...]:
+        """Number of work items in (x, y, z)-order."""
         return self._num_work_items
 
     @property
@@ -49,7 +51,7 @@ class GpuThreadsRange:
 
     @staticmethod
     def _from_full_ispace(ispace: FullIterationSpace) -> GpuThreadsRange:
-        dimensions = ispace.dimensions_in_loop_order()
+        dimensions = ispace.dimensions_in_loop_order()[::-1]
         if len(dimensions) > 3:
             raise NotImplementedError(
                 f"Cannot create a GPU threads range for an {len(dimensions)}-dimensional iteration space"

tests/nbackend/kernelcreation/platform/test_gpu_platforms.py

@@ -28,10 +28,15 @@ def test_thread_range(platform_class, layout):
 
     assert threads_range.dim == dim
     
-    loop_order = archetype_field.layout
+    match layout:
+        case "fzyx" | "zyxf" | "f":
+            indexing_order = [0, 1, 2]
+        case "c":
+            indexing_order = [2, 1, 0]
 
     for i in range(dim):
-        coordinate = loop_order[i]
+        #   Slowest to fastest coordinate
+        coordinate = indexing_order[i]
         dimension = ispace.dimensions[coordinate]
         witems = threads_range.num_work_items[i]
         desired = dimension.stop - dimension.start

tests/nbackend/kernelcreation/test_domain_kernels.py

@@ -30,7 +30,7 @@ def test_filter_kernel(target):
     ast = create_kernel(asms, gen_config)
     kernel = ast.compile()
 
-    src_arr = xp.ones((42, 42))
+    src_arr = xp.ones((42, 31))
     dst_arr = xp.zeros_like(src_arr)
 
     kernel(src=src_arr, dst=dst_arr, weight=2.0)
@@ -55,7 +55,7 @@ def test_filter_kernel_fixedsize(target):
         [1, 1, 1]
     ]
 
-    src_arr = xp.ones((42, 42))
+    src_arr = xp.ones((42, 31))
     dst_arr = xp.zeros_like(src_arr)
 
     src = Field.create_from_numpy_array("src", src_arr)