From: Steinar H. Gunderson <sgunderson@bigfoot.com>
Date: Wed, 12 Mar 2014 00:24:39 +0000 (+0100)
Subject: Add more unit tests for fp16.
X-Git-Tag: 1.0~14
X-Git-Url: https://git.sesse.net/?p=movit;a=commitdiff_plain;h=4b2ecf9112a34baf2b41aeb4dffeaa698bb9f79a

Add more unit tests for fp16.

This tests a few edge cases that are not adequately covered by the
random fp32 tests; in particular, the round-to-even logic had
no test coverage, which is bad.
---

diff --git a/fp16_test.cpp b/fp16_test.cpp
index d5d7fc0..3deb74b 100644
--- a/fp16_test.cpp
+++ b/fp16_test.cpp
@@ -16,9 +16,19 @@ TEST(FP16Test, Simple) {
 	EXPECT_DOUBLE_EQ(0.333251953125, fp16_to_fp64(0x3555));
 }
 
-TEST(FP16Test, NaN) {
-	EXPECT_EQ(0xfe00, fp64_to_fp16(0.0 / 0.0));
-	EXPECT_TRUE(isnan(fp16_to_fp64(0xfe00)));
+TEST(FP16Test, RoundToNearestEven) {
+	ASSERT_DOUBLE_EQ(1.0, fp16_to_fp64(0x3c00));
+
+	double x0 = fp16_to_fp64(0x3c00);
+	double x1 = fp16_to_fp64(0x3c01);
+	double x2 = fp16_to_fp64(0x3c02);
+	double x3 = fp16_to_fp64(0x3c03);
+	double x4 = fp16_to_fp64(0x3c04);
+
+	EXPECT_EQ(0x3c00, fp64_to_fp16(0.5 * (x0 + x1)));
+	EXPECT_EQ(0x3c02, fp64_to_fp16(0.5 * (x1 + x2)));
+	EXPECT_EQ(0x3c02, fp64_to_fp16(0.5 * (x2 + x3)));
+	EXPECT_EQ(0x3c04, fp64_to_fp16(0.5 * (x3 + x4)));
 }
 
 union fp64 {
@@ -30,6 +40,44 @@ union fp32 {
 	unsigned int u;
 };
 
+TEST(FP16Test, NaN) {
+	EXPECT_EQ(0xfe00, fp64_to_fp16(0.0 / 0.0));
+	EXPECT_TRUE(isnan(fp16_to_fp64(0xfe00)));
+
+	fp64 borderline_inf;
+	borderline_inf.ll = 0x7ff0000000000000ull;
+	fp64 borderline_nan;
+	borderline_nan.ll = 0x7ff0000000000001ull;
+
+	ASSERT_FALSE(isfinite(borderline_inf.f));
+	ASSERT_FALSE(isnan(borderline_inf.f));
+
+	ASSERT_FALSE(isfinite(borderline_nan.f));
+	ASSERT_TRUE(isnan(borderline_nan.f));
+
+	double borderline_inf_roundtrip = fp16_to_fp64(fp64_to_fp16(borderline_inf.f));
+	double borderline_nan_roundtrip = fp16_to_fp64(fp64_to_fp16(borderline_nan.f));
+
+	EXPECT_FALSE(isfinite(borderline_inf_roundtrip));
+	EXPECT_FALSE(isnan(borderline_inf_roundtrip));
+
+	EXPECT_FALSE(isfinite(borderline_nan_roundtrip));
+	EXPECT_TRUE(isnan(borderline_nan_roundtrip));
+}
+
+TEST(FP16Test, Denormals) {
+	const double smallest_fp16_denormal = 5.9604644775390625e-08;
+	EXPECT_EQ(0x0001, fp64_to_fp16(smallest_fp16_denormal));
+	EXPECT_EQ(0x0000, fp64_to_fp16(0.5 * smallest_fp16_denormal));  // Round-to-even.
+	EXPECT_EQ(0x0001, fp64_to_fp16(0.51 * smallest_fp16_denormal));
+	EXPECT_EQ(0x0002, fp64_to_fp16(1.5 * smallest_fp16_denormal));
+
+	const double smallest_fp16_non_denormal = 6.103515625e-05;
+	EXPECT_EQ(0x0400, fp64_to_fp16(smallest_fp16_non_denormal));
+	EXPECT_EQ(0x0400, fp64_to_fp16(smallest_fp16_non_denormal - 0.5 * smallest_fp16_denormal));  // Round-to-even.
+	EXPECT_EQ(0x03ff, fp64_to_fp16(smallest_fp16_non_denormal - smallest_fp16_denormal));
+}
+
 // Randomly test a large number of fp64 -> fp32 conversions, comparing
 // against the FPU.
 TEST(FP16Test, FP32ReferenceDownconvert) {