pan/lib: Add a test for pan_compute_npot_divisor

This ensures proper behaviors of pan_compute_npot_divisor by using the
same algorithm as the hardware to perform the division.

Signed-off-by: Mary Guillemard <mary.guillemard@collabora.com>
Reviewed-by: Olivia Lee <olivia.lee@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/35490>

src/panfrost/lib/meson.build

@@ -70,6 +70,19 @@ libpanfrost_dep = declare_dependency(
 )
 
 if with_tests
+  test(
+    'panfrost_attribute',
+    executable(
+      'panfrost_attribute_test',
+      files('tests/test-attribute.c'),
+      c_args : [c_msvc_compat_args, no_override_init_args],
+      gnu_symbol_visibility : 'hidden',
+      include_directories : [inc_include, inc_src],
+      dependencies: [libpanfrost_dep],
+    ),
+    suite : ['panfrost'],
+  )
+
   test(
     'panfrost_blend',
     executable(

src/panfrost/lib/tests/test-attribute.c

@@ -0,0 +1,67 @@
+/*
+ * Copyright 2025 Collabora Ltd.
+ * SPDX-License-Identifier: MIT
+ */
+#include "pan_encoder.h"
+
+struct test {
+   const char *label;
+   uint32_t offset_id;
+   uint32_t divisor;
+};
+
+#define TEST_DEF(label, offset_id, divisor) {label, offset_id, divisor}
+
+static const struct test attribute_tests[] = {
+   TEST_DEF("Sanity check even", 2, 2),
+   TEST_DEF("Sanity check odd", 9, 3),
+   TEST_DEF("Sanity check random #1", 42, 3),
+   TEST_DEF("Sanity check random #2", 999, 3),
+   TEST_DEF("Sanity check max #1", UINT32_MAX, UINT32_MAX),
+   TEST_DEF("Sanity check max #2", UINT32_MAX, INT32_MAX),
+   TEST_DEF("Regression test case #1", 404896682, 444453),
+   TEST_DEF("Regression test case #2", 449209605, 980807),
+   TEST_DEF("Regression test case #3", 412962763, 103240691),
+   TEST_DEF("Regression test case #4", 1269169964, 507465),
+   TEST_DEF("Regression test case #5", 1771745081, 6867229),
+};
+
+static uint32_t
+compute_effective_id(uint64_t offset_id, uint64_t r, uint64_t e, uint64_t d)
+{
+   return (offset_id + e) * (d + (1u << 31)) / ((uint64_t)1 << (32 + r));
+}
+
+#define ASSERT_EQ(x, y)                                                        \
+   do {                                                                        \
+      if (x == y) {                                                            \
+         nr_pass++;                                                            \
+      } else {                                                                 \
+         nr_fail++;                                                            \
+         fprintf(stderr, "%s: Assertion failed %s (%x) != %s (%x)\n", T.label, \
+                 #x, x, #y, y);                                                \
+      }                                                                        \
+   } while (0)
+
+int
+main(int argc, const char **argv)
+{
+   unsigned nr_pass = 0, nr_fail = 0;
+
+   for (unsigned i = 0; i < ARRAY_SIZE(attribute_tests); ++i) {
+      struct test T = attribute_tests[i];
+
+      uint32_t e;
+      uint32_t r;
+      uint32_t d = pan_compute_npot_divisor(T.divisor, &r, &e);
+
+      uint32_t expected_effective_id = T.offset_id / T.divisor;
+      uint32_t computed_effective_id =
+         compute_effective_id(T.offset_id, r, e, d);
+
+      ASSERT_EQ(expected_effective_id, computed_effective_id);
+   }
+
+   printf("Passed %u/%u\n", nr_pass, nr_pass + nr_fail);
+   return nr_fail ? 1 : 0;
+}