[FXCRT] Add unit tests for FXSYS_round()
There were none before, now there can be some. This exposes an issue at
the edges of the integer range, where a float larger than the maximum
value of a signed 32 bit integer returns a value of the maximum negative
integer.
Bug: chromium:611744
Change-Id: Iad8551a17cac69f2078943bbf80d1211883ae974
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/60450
Commit-Queue: Lei Zhang <thestig@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
diff --git a/core/fxcrt/fx_system_unittest.cpp b/core/fxcrt/fx_system_unittest.cpp
index d32c8e2..83ac625 100644
--- a/core/fxcrt/fx_system_unittest.cpp
+++ b/core/fxcrt/fx_system_unittest.cpp
@@ -74,6 +74,57 @@
} // namespace
+TEST(fxcrt, FXSYS_round) {
+ EXPECT_EQ(0, FXSYS_round(0.0f));
+ EXPECT_EQ(0, FXSYS_round(-0.0f));
+ EXPECT_EQ(0, FXSYS_round(0.00001f));
+ EXPECT_EQ(0, FXSYS_round(-0.00001f));
+ EXPECT_EQ(3, FXSYS_round(3.14159f));
+ EXPECT_EQ(4, FXSYS_round(3.5f));
+
+ // Check for smallest non-zero float values.
+ EXPECT_EQ(0, FXSYS_round(std::numeric_limits<float>::min()));
+ EXPECT_EQ(0, FXSYS_round(-std::numeric_limits<float>::min()));
+
+ // Function is a wrapper around standard C library function round(), so
+ // returns the integral value that is nearest to x, with halfway cases
+ // rounded away from zero.
+ EXPECT_EQ(-3, FXSYS_round(-3.14159f));
+ EXPECT_EQ(-4, FXSYS_round(-3.5f));
+
+ // Positive rounding stops at maximum int.
+ // MAX_INT=0x7FFFFFFF=2147483647=2.147483647e+9
+ // In IEEE-754 format, 2^31 yields exponent of 0x9E with mantissa of all
+ // zeroes which is 0x4f000000=2.14748365e+9, which is beyond max integer.
+ // Going to next smallest float by minus one from exponent and mantissa of
+ // all ones yields binary float representation of 0x4EFFFFFF=2.14748352e+9,
+ // which is 2147483520.
+ EXPECT_EQ(2147483520, FXSYS_round(2.14748352e+9f));
+
+ // Using a slightly larger value, expect to see it be capped at MAX_INT.
+ // Instead erroneously seeing a return of MIN_INT. crbug.com/611744
+ EXPECT_EQ(-2147483648, FXSYS_round(2.14748365e+9f));
+
+ EXPECT_EQ(2147483647, FXSYS_round(2.14748365e+10f));
+ EXPECT_EQ(2147483647, FXSYS_round(std::numeric_limits<float>::max()));
+
+ // Negative rounding stops at minimum int.
+ // MIN_INT=0x80000000=-2147483648,=-2.147483648e+9
+ // In IEEE-754 format, 2^31 yields exponent of 0x9E with mantissa of all
+ // zeroes which is 0x4f000000=2.14748365e+9, and the sign bit set, which
+ // is 0xCF000000 and exactly matches the minimum integer. Going to next
+ // smallest negative float by minus one from exponent and mantissa of all
+ // ones yields binary float representation of 0xCEFFFFFF=-2.14748352e+9,
+ // which is -2147483520.
+ EXPECT_EQ(-2147483648, FXSYS_round(-2.147483648e+10f));
+ EXPECT_EQ(-2147483648, FXSYS_round(-2.147483648e+9f));
+ EXPECT_EQ(-2147483520, FXSYS_round(-2.14748352e+9f));
+ EXPECT_EQ(-2147483648, FXSYS_round(-std::numeric_limits<float>::max()));
+
+ // NaN should give zero.
+ EXPECT_EQ(0, FXSYS_round(NAN));
+}
+
TEST(fxcrt, FXSYS_itoa_InvalidRadix) {
char buf[32];
