[BUGFIX] GPU slicing

Fixes #90 (closed)

tests/test_gpu.py

@@ -2,6 +2,7 @@ import pytest
 
 import numpy as np
 import sympy as sp
+import math
 from scipy.ndimage import convolve
 
 from pystencils import Assignment, Field, fields, CreateKernelConfig, create_kernel, Target, get_code_str
@@ -231,15 +232,26 @@ def test_guards_with_iteration_slices(start, end, step, shape):
     field_1 = fields(f"f(1) : double{list(shape)}")
     assignment = Assignment(field_1.center, 1)
     ast = create_kernel(assignment, config=kernel_config_gpu)
-
     code_str = get_code_str(ast)
 
     test_strings = list()
+    iteration_ranges = list()
     for i, s in enumerate(iter_slice):
-        end = shape[i] + s.stop
-        end = end // s.step
-        test_strings.append(f"{s.start} < {end}")
-
+        e = ((shape[i] + end) - s.start) / s.step
+        e = math.ceil(e) + s.start
+        test_strings.append(f"{s.start} < {e}")
+
+        a = s.start
+        counter = 0
+        while a < e:
+            a += 1
+            counter += 1
+        iteration_ranges.append(counter)
+
+    # check if the expected if statement is in the GPU code
     for s in test_strings:
         assert s in code_str
 
+    # check if these bounds lead to same lengths as the range function would produce
+    for i in range(len(iter_slice)):
+        assert iteration_ranges[i] == len(range(iter_slice[i].start, shape[i] + end, iter_slice[i].step))