AK: Make FixedPoint(FloatingPoint) ctor round instead of truncating

This is needed to have code for creating an in-memory sRGB profile using
the (floating-ppoint) numbers from the sRGB spec and having the
fixed-point values in the profile match what they are in other software
(such as GIMP).

It has the side effect of making the FixedPoint ctor no longer constexpr
(which seems fine; nothing was currently relying on that).

Some of FixedPoint's member functions don't round yet, which requires
tweaking a test.

AK/FixedPoint.h

@@ -36,11 +36,13 @@ public:
     {
     }
 
+#ifndef KERNEL
     template<FloatingPoint F>
-    constexpr FixedPoint(F value)
+    FixedPoint(F value)
-        : m_value(static_cast<Underlying>(value * (static_cast<Underlying>(1) << precision)))
+        : m_value(round_to<Underlying>(value * (static_cast<Underlying>(1) << precision)))
     {
     }
+#endif
 
     template<size_t P, typename U>
     explicit constexpr FixedPoint(FixedPoint<P, U> const& other)

Tests/AK/TestFixedPoint.cpp

@@ -72,6 +72,16 @@ TEST_CASE(rounding)
     EXPECT_EQ(Type(-1.5).lfloor(), -2);
     EXPECT_EQ(Type(-1.5).lceil(), -1);
     EXPECT_EQ(Type(-1.5).ltrunk(), -1);
+
+    // Check that sRGB TRC curve parameters match the s15fixed16 values stored in Gimp's built-in profile.
+    // (This only requires that the FixedPoint<> constructor rounds before truncating to the fixed-point value,
+    // as it should anyways.)
+    using S15Fixed16 = FixedPoint<16, i32>;
+    EXPECT_EQ(S15Fixed16(2.4).raw(), 0x26666);
+    EXPECT_EQ(S15Fixed16(1 / 1.055).raw(), 0xf2a7);
+    EXPECT_EQ(S15Fixed16(0.055 / 1.055).raw(), 0xd59);
+    EXPECT_EQ(S15Fixed16(1 / 12.92).raw(), 0x13d0);
+    EXPECT_EQ(S15Fixed16(0.04045).raw(), 0xa5b);
 }
 
 TEST_CASE(logarithm)
@@ -115,7 +125,7 @@ TEST_CASE(cast)
 {
     FixedPoint<16, u32> downcast_value1(FixedPoint<32, u64>(123.4567));
     EXPECT((double)downcast_value1 >= 123.4566 && (double)downcast_value1 <= 123.4568);
-    static constexpr FixedPoint<32, u64> value1(321.7654);
+    static FixedPoint<32, u64> const value1(321.7654);
     downcast_value1 = value1;
     EXPECT((double)downcast_value1 >= 321.7653 && (double)downcast_value1 <= 321.7655);
     FixedPoint<6, u32> downcast_value2(FixedPoint<32, u64>(4567.123456));
@@ -150,12 +160,12 @@ TEST_CASE(formatter)
     EXPECT_EQ(DeprecatedString::formatted("{}", FixedPoint<4>(123.456)), "123.4375"sv);
     EXPECT_EQ(DeprecatedString::formatted("{}", FixedPoint<4>(-123.456)), "-123.4375"sv);
     EXPECT_EQ(DeprecatedString::formatted("{}", FixedPoint<16> {}), "0"sv);
-    EXPECT_EQ(DeprecatedString::formatted("{}", FixedPoint<16>(0.1)), "0.09999"sv);
+    EXPECT_EQ(DeprecatedString::formatted("{}", FixedPoint<16>(0.1)), "0.100006"sv);
-    EXPECT_EQ(DeprecatedString::formatted("{}", FixedPoint<16>(0.02)), "0.019989"sv);
+    EXPECT_EQ(DeprecatedString::formatted("{}", FixedPoint<16>(0.02)), "0.020004"sv);
-    EXPECT_EQ(DeprecatedString::formatted("{}", FixedPoint<16>(0.003)), "0.00299"sv);
+    EXPECT_EQ(DeprecatedString::formatted("{}", FixedPoint<16>(0.003)), "0.003005"sv);
     EXPECT_EQ(DeprecatedString::formatted("{}", FixedPoint<16>(0.0004)), "0.000396"sv);
     EXPECT_EQ(DeprecatedString::formatted("{}", FixedPoint<16>(0.0000000005)), "0"sv);
-    EXPECT_EQ(DeprecatedString::formatted("{}", FixedPoint<16>(-0.1)), "-0.099991"sv);
+    EXPECT_EQ(DeprecatedString::formatted("{}", FixedPoint<16>(-0.1)), "-0.100007"sv);
-    EXPECT_EQ(DeprecatedString::formatted("{}", FixedPoint<16>(-0.02)), "-0.01999"sv);
+    EXPECT_EQ(DeprecatedString::formatted("{}", FixedPoint<16>(-0.02)), "-0.020005"sv);
     EXPECT_EQ(DeprecatedString::formatted("{}", FixedPoint<16>(-0.0000000005)), "0"sv);
 }

Tests/LibEDID/TestEDID.cpp

@@ -520,10 +520,19 @@ TEST_CASE(dmt_frequency)
 {
     auto* dmt = EDID::DMT::find_timing_by_dmt_id(0x4);
     EXPECT(dmt);
-    static constexpr FixedPoint<16, u32> expected_vertical_frequency(59.940);
+
-    EXPECT(dmt->vertical_frequency_hz() == expected_vertical_frequency);
+    // FIXME: Use the FixedPoint(double) ctor like `expected_vertical_frequency(59.940)` instead of
-    static constexpr FixedPoint<16, u32> expected_horizontal_frequency(31.469);
+    //        dividing by 1000 in the next line once FixedPoint::operator/ rounds.
-    EXPECT(dmt->horizontal_frequency_khz() == expected_horizontal_frequency);
+    //        1. DMT.cpp is built as part of the kernel (despite being in Userland/)
+    //        2. The Kernel can't use floating point
+    //        3. So it has to use FixedPoint(59940) / 1000
+    //        4. The FixedPoint(double) ctor rounds, but FixedPoint::operator/ currently doesn't,
+    //           so FixedPoint(59.940) has a different lowest bit than
+    //           FixedPoint(59940) / 1000. So the test can't use the FixedPoint(double) ctor at the moment.
+    static FixedPoint<16, u32> const expected_vertical_frequency(59940);
+    EXPECT(dmt->vertical_frequency_hz() == expected_vertical_frequency / 1000);
+    static FixedPoint<16, u32> const expected_horizontal_frequency(31469);
+    EXPECT(dmt->horizontal_frequency_khz() == expected_horizontal_frequency / 1000);
 }
 
 TEST_CASE(vic)