From 48712168b8222d4e48371fa1bd803d83fd90334d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?L=C3=A9o=20Lam?= <leo@leolam.fr>
Date: Thu, 28 Jan 2021 12:45:50 +0100
Subject: MathUtil: Add SaturatingCast to cast floats more safely

---
 Source/UnitTests/Common/MathUtilTest.cpp | 42 ++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

(limited to 'Source/UnitTests/Common/MathUtilTest.cpp')

diff --git a/Source/UnitTests/Common/MathUtilTest.cpp b/Source/UnitTests/Common/MathUtilTest.cpp
index c0609bbb92..e31777d16d 100644
--- a/Source/UnitTests/Common/MathUtilTest.cpp
+++ b/Source/UnitTests/Common/MathUtilTest.cpp
@@ -26,3 +26,45 @@ TEST(MathUtil, NextPowerOf2)
   EXPECT_EQ(8U, MathUtil::NextPowerOf2(6));
   EXPECT_EQ(0x40000000U, MathUtil::NextPowerOf2(0x23456789));
 }
+
+TEST(MathUtil, SaturatingCast)
+{
+  // Cast from an integer type to a smaller type
+  EXPECT_EQ(255u, (MathUtil::SaturatingCast<u8, int>(1000)));
+  EXPECT_EQ(255u, (MathUtil::SaturatingCast<u8, u16>(1000u)));
+  EXPECT_EQ(255u, (MathUtil::SaturatingCast<u8, std::size_t>(1000)));
+
+  // Cast from a signed integer type
+  EXPECT_EQ(0u, (MathUtil::SaturatingCast<u8, int>(-1)));
+  EXPECT_EQ(0u, (MathUtil::SaturatingCast<u8, int>(-1000)));
+  EXPECT_EQ(0u, (MathUtil::SaturatingCast<u32, int>(-1)));
+  EXPECT_EQ(-1000, (MathUtil::SaturatingCast<s16, int>(-1000)));
+  EXPECT_EQ(-1000, (MathUtil::SaturatingCast<int, int>(-1000)));
+  EXPECT_EQ(-1000, (MathUtil::SaturatingCast<s64, int>(-1000)));
+
+  // Cast from an unsigned integer type to a smaller integer type
+  EXPECT_EQ(0x7fff, (MathUtil::SaturatingCast<s16, u32>(0xffffffffu)));
+  EXPECT_EQ(0x7fffffff, (MathUtil::SaturatingCast<int, u32>(0xffffffffu)));
+
+  // Cast from a floating point type to an integer type
+  EXPECT_EQ(255u, MathUtil::SaturatingCast<u8>(1234.0));
+  EXPECT_EQ(0u, MathUtil::SaturatingCast<u8>(-1234.0));
+  EXPECT_EQ(127, MathUtil::SaturatingCast<s8>(5678.0));
+  EXPECT_EQ(-128, MathUtil::SaturatingCast<s8>(-5678.0));
+  EXPECT_EQ(65535u, MathUtil::SaturatingCast<u16>(999999.0));
+
+  // Negative zero
+  EXPECT_EQ(0u, MathUtil::SaturatingCast<u8>(0.0));
+  EXPECT_EQ(0u, MathUtil::SaturatingCast<u8>(-0.0));
+  EXPECT_EQ(0, MathUtil::SaturatingCast<s8>(0.0));
+  EXPECT_EQ(0, MathUtil::SaturatingCast<s8>(-0.0));
+
+  // Edge cases
+  EXPECT_EQ(std::numeric_limits<s32>::max(),
+            MathUtil::SaturatingCast<s32>(std::numeric_limits<float>::infinity()));
+  EXPECT_EQ(std::numeric_limits<s32>::min(),
+            MathUtil::SaturatingCast<s32>(-std::numeric_limits<float>::infinity()));
+  // 16777217 = 2^24 + 1 is the first integer that cannot be represented correctly with a f32.
+  EXPECT_EQ(16777216, MathUtil::SaturatingCast<s32>(float(16777216)));
+  EXPECT_EQ(16777216, MathUtil::SaturatingCast<s32>(float(16777217)));
+}
-- 
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