From 13c3a45a9832188783e0857b700b2f4d5e3d6235 Mon Sep 17 00:00:00 2001
From: Dmitry Pentin <riotbr3aker@gmail.com>
Date: Tue, 13 Jul 2021 17:53:17 +0300
Subject: [PATCH] Added DivideCeil

---
 src/ImageSharp/Common/Helpers/Numerics.cs     |  8 +++++
 .../Jpeg/Components/Decoder/JpegFrame.cs      |  4 +--
 .../ImageSharp.Tests/Common/NumericsTests.cs  | 34 +++++++++++++++++--
 3 files changed, 41 insertions(+), 5 deletions(-)

diff --git a/src/ImageSharp/Common/Helpers/Numerics.cs b/src/ImageSharp/Common/Helpers/Numerics.cs
index db65b84cca..ba5c588ca5 100644
--- a/src/ImageSharp/Common/Helpers/Numerics.cs
+++ b/src/ImageSharp/Common/Helpers/Numerics.cs
@@ -879,5 +879,13 @@ namespace SixLabors.ImageSharp
                 (IntPtr)(int)((value * 0x07C4ACDDu) >> 27)); // uint|long -> IntPtr cast on 32-bit platforms does expensive overflow checks not needed here
         }
 #endif
+
+        /// <summary>
+        /// Fast division with ceiling for <see cref="uint"/> numbers.
+        /// </summary>
+        /// <param name="value">Divident value.</param>
+        /// <param name="divisor">Divisor value.</param>
+        /// <returns>Ceiled division result.</returns>
+        public static uint DivideCeil(uint value, uint divisor) => (value + divisor - 1) / divisor;
     }
 }
diff --git a/src/ImageSharp/Formats/Jpeg/Components/Decoder/JpegFrame.cs b/src/ImageSharp/Formats/Jpeg/Components/Decoder/JpegFrame.cs
index 9f89fd085f..3a136b4103 100644
--- a/src/ImageSharp/Formats/Jpeg/Components/Decoder/JpegFrame.cs
+++ b/src/ImageSharp/Formats/Jpeg/Components/Decoder/JpegFrame.cs
@@ -103,8 +103,8 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
         /// </summary>
         public void InitComponents()
         {
-            this.McusPerLine = (int)MathF.Ceiling(this.PixelWidth / 8F / this.MaxHorizontalFactor);
-            this.McusPerColumn = (int)MathF.Ceiling(this.PixelHeight / 8F / this.MaxVerticalFactor);
+            this.McusPerLine = (int)Numerics.DivideCeil((uint)this.PixelWidth, (uint)this.MaxHorizontalFactor * 8);
+            this.McusPerColumn = (int)Numerics.DivideCeil((uint)this.PixelHeight, (uint)this.MaxVerticalFactor * 8);
 
             for (int i = 0; i < this.ComponentCount; i++)
             {
diff --git a/tests/ImageSharp.Tests/Common/NumericsTests.cs b/tests/ImageSharp.Tests/Common/NumericsTests.cs
index 29eae6d488..62819af493 100644
--- a/tests/ImageSharp.Tests/Common/NumericsTests.cs
+++ b/tests/ImageSharp.Tests/Common/NumericsTests.cs
@@ -34,7 +34,7 @@ namespace SixLabors.ImageSharp.Tests.Common
             int expected = 0;
             int actual = Numerics.Log2(value);
 
-            Assert.True(expected == actual, $"Expected: {expected}, Actual: {actual}");
+            Assert.Equal(expected, actual);
         }
 
         [Fact]
@@ -47,7 +47,7 @@ namespace SixLabors.ImageSharp.Tests.Common
                 int expected = i;
                 int actual = Numerics.Log2(value);
 
-                Assert.True(expected == actual, $"Expected: {expected}, Actual: {actual}");
+                Assert.Equal(expected, actual);
             }
         }
 
@@ -66,7 +66,35 @@ namespace SixLabors.ImageSharp.Tests.Common
                 int expected = Log2_ReferenceImplementation(value);
                 int actual = Numerics.Log2(value);
 
-                Assert.True(expected == actual, $"Expected: {expected}, Actual: {actual}");
+                Assert.Equal(expected, actual);
+            }
+        }
+
+        private static uint DivideCeil_ReferenceImplementation(uint value, uint divisor) => (uint)MathF.Ceiling((float)value / divisor);
+
+        [Fact]
+        public void DivideCeil_DivideZero()
+        {
+            uint expected = 0;
+            uint actual = Numerics.DivideCeil(0, 100);
+
+            Assert.Equal(expected, actual);
+        }
+
+        [Theory]
+        [InlineData(1, 100)]
+        public void DivideCeil_RandomValues(int seed, int count)
+        {
+            var rng = new Random(seed);
+            for (int i = 0; i < count; i++)
+            {
+                uint value = (uint)rng.Next();
+                uint divisor = (uint)rng.Next();
+
+                uint expected = DivideCeil_ReferenceImplementation(value, divisor);
+                uint actual = Numerics.DivideCeil(value, divisor);
+
+                Assert.True(expected == actual, $"Expected: {expected}\nActual: {actual}\n{value} / {divisor} = {expected}");
             }
         }
     }