From 858964edbc642178cab454cef4baa5d05338b34f Mon Sep 17 00:00:00 2001
From: mlemanczyk <marek@lemanczyk.eu>
Date: Sun, 26 Mar 2023 23:38:21 +0200
Subject: [PATCH] MathUtils added

---
 Recyclable.Collections/MathUtils.cs           | 42 +++++++++++++++++++
 Recyclable.CollectionsTests/MathUtilsTests.cs | 32 ++++++++++++++
 2 files changed, 74 insertions(+)
 create mode 100644 Recyclable.Collections/MathUtils.cs
 create mode 100644 Recyclable.CollectionsTests/MathUtilsTests.cs

diff --git a/Recyclable.Collections/MathUtils.cs b/Recyclable.Collections/MathUtils.cs
new file mode 100644
index 0000000..30e5434
--- /dev/null
+++ b/Recyclable.Collections/MathUtils.cs
@@ -0,0 +1,42 @@
+using System.Runtime.CompilerServices;
+
+namespace Recyclable.Collections
+{
+	public static class MathUtils
+	{
+		private static long[] Pow2 = new long[]
+		{
+			1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192, 16384,
+			32768, 65536, 131072, 262144, 524288, 1048576, 2097152, 4194304,
+			8388608, 16777216, 33554432, 67108864, 134217728, 268435456,
+			536870912, 1073741824, 2147483648
+		};
+
+		[MethodImpl(MethodImplOptions.AggressiveInlining)]
+		public static bool IsPow2(int value) => Array.BinarySearch(Pow2, value) >= 0;
+
+		[MethodImpl(MethodImplOptions.AggressiveInlining)]
+		public static int GetPow2Shift(int value) => Array.BinarySearch(Pow2, value);
+
+		[MethodImpl(MethodImplOptions.AggressiveInlining)]
+		public static long DivMod(long number, int divider, out long remainder)
+		{
+			if (number >= divider << 4)
+			{
+				return Math.DivRem(number, divider, out remainder);
+			}
+			else
+			{
+				int result = 0;
+				remainder = number;
+				while (remainder >= divider)
+				{
+					remainder -= divider;
+					result++;
+				}
+
+				return result;
+			}
+		}
+	}
+}
diff --git a/Recyclable.CollectionsTests/MathUtilsTests.cs b/Recyclable.CollectionsTests/MathUtilsTests.cs
new file mode 100644
index 0000000..40c9362
--- /dev/null
+++ b/Recyclable.CollectionsTests/MathUtilsTests.cs
@@ -0,0 +1,32 @@
+using FluentAssertions;
+using Recyclable.Collections;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Recyclable.CollectionsTests
+{
+	public class MathUtilsTests
+	{
+		[Theory]
+		[InlineData(int.MaxValue / 1024, int.MaxValue / 10 / 1024)]
+		public void DivMod(long testNumber, int blockSize)
+		{
+			for (var testCase = testNumber; testCase >= 0; testCase--)
+			{
+				// Prepare
+				var expectedResult = testCase / blockSize;
+				var expectedRemainder = testCase % blockSize;
+
+				// Act
+				var actualResult = MathUtils.DivMod(testCase, blockSize, out long actualRemainder);
+
+				// Validate
+				_ = actualResult.Should().Be(expectedResult);
+				_ = actualRemainder.Should().Be(expectedRemainder);
+			}
+		}
+	}
+}