util: Add some unit tests of the half-float conversions.

Make sure that we're handling nans/infs correctly, in particular only
generating quiet nans when given a quiet nan.  This catches the previous
qNaN fix.

Reviewed-by: Chia-I Wu <olvaffe@gmail.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16233>

src/util/meson.build

@@ -324,6 +324,7 @@ if with_tests
     'tests/dag_test.cpp',
     'tests/fast_idiv_by_const_test.cpp',
     'tests/fast_urem_by_const_test.cpp',
+    'tests/half_float_test.cpp',
     'tests/int_min_max.cpp',
     'tests/rb_tree_test.cpp',
     'tests/register_allocate_test.cpp',

src/util/tests/half_float_test.cpp

@@ -0,0 +1,134 @@
+/*
+ * Copyright © 2021 Intel Corporation
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ */
+
+#include <math.h>
+#include <gtest/gtest.h>
+
+#include "util/half_float.h"
+#include "util/u_math.h"
+
+/* math.h has some defines for these, but they have some compiler dependencies
+ * and can potentially raise exceptions.
+ */
+#define TEST_POS_INF (uif(0x7f800000))
+#define TEST_NEG_INF (uif(0xff800000))
+#define TEST_NAN (uif(0x7fc00000))
+
+#define HALF_POS_INF 0x7c00
+#define HALF_NEG_INF 0xfc00
+#define HALF_NAN 0x7e00
+
+#if defined(ANDROID) || defined (__MINGW32__)
+/* Android and mingw were missing this function, roll our own as a best effort. */
+static bool issignaling(float x)
+{
+   uint32_t ui = fui(x);
+   return (((ui >> 23) & 0xff) == 0xff) && !(ui & (1 << 22));
+}
+#endif
+
+/* Sanity test our test values */
+TEST(half_to_float_test, nan_test)
+{
+   EXPECT_TRUE(isinf(TEST_POS_INF));
+   EXPECT_TRUE(isinf(TEST_NEG_INF));
+
+   EXPECT_TRUE(isnan(TEST_NAN));
+   /* Make sure that our 32-bit float nan test value we're using is a
+    * non-signaling NaN.  The sign of the bit for signaling was apparently
+    * different on some old processors (PA-RISC, MIPS?).  This test value should
+    * cover Intel, ARM, and PPC, for sure.
+    */
+   EXPECT_FALSE(issignaling(TEST_NAN));
+}
+
+static void
+test_half_to_float_limits(float (*func)(uint16_t))
+{
+   /* Positive and negative 0. */
+   EXPECT_EQ(func(0), 0.0f);
+   EXPECT_EQ(fui(func(0x8000)), fui(-0.0f));
+
+   /* Max normal number */
+   EXPECT_EQ(func(0x7bff), 65504.0f);
+
+   float nan = func(HALF_NAN);
+   EXPECT_TRUE(isnan(nan));
+   EXPECT_FALSE(issignaling(nan));
+
+   /* inf */
+   EXPECT_EQ(func(HALF_POS_INF), TEST_POS_INF);
+   /* -inf */
+   EXPECT_EQ(func(HALF_NEG_INF), TEST_NEG_INF);
+}
+
+/* Test the optionally HW instruction-using path. */
+TEST(half_to_float_test, half_to_float_test)
+{
+   test_half_to_float_limits(_mesa_half_to_float);
+}
+
+TEST(half_to_float_test, half_to_float_slow_test)
+{
+   test_half_to_float_limits(_mesa_half_to_float_slow);
+}
+
+static void
+test_float_to_half_limits(uint16_t (*func)(float))
+{
+   /* Positive and negative 0. */
+   EXPECT_EQ(func(0.0f), 0);
+   EXPECT_EQ(func(-0.0f), 0x8000);
+
+   /* Max normal number */
+   EXPECT_EQ(func(65504.0f), 0x7bff);
+
+   uint16_t nan = func(TEST_NAN);
+   EXPECT_EQ((nan & 0xfc00), 0x7c00); /* exponent is all 1s */
+   EXPECT_TRUE(nan & (1 << 9)); /* mantissa is quiet nan */
+
+   EXPECT_EQ(func(TEST_POS_INF), HALF_POS_INF);
+   EXPECT_EQ(func(TEST_NEG_INF), HALF_NEG_INF);
+}
+
+TEST(float_to_half_test, float_to_half_test)
+{
+   test_float_to_half_limits(_mesa_float_to_half);
+}
+
+TEST(float_to_float16_rtne_test, float_to_float16_rtne_test)
+{
+   test_float_to_half_limits(_mesa_float_to_float16_rtne);
+}
+
+/* no rtne_slow variant -- rtne is just _mesa_float_to_half(). */
+
+TEST(float_to_float16_rtz_test, float_to_float16_rtz_test)
+{
+   test_float_to_half_limits(_mesa_float_to_float16_rtz);
+}
+
+TEST(float_to_float16_rtz_slow_test, float_to_float16_rtz_test)
+{
+   test_float_to_half_limits(_mesa_float_to_float16_rtz_slow);
+}