From 1f86ef2c598a19d2baabd2cdcd0364d9fe6512a3 Mon Sep 17 00:00:00 2001
From: mlemanczyk <marek@lemanczyk.eu>
Date: Mon, 27 Mar 2023 01:12:39 +0200
Subject: [PATCH] MathUtils.IsPow2 & MathUtils.GetPow2Shift performance
 improvements.

---
 Recyclable.Collections/MathUtils.cs           |  7 ++-
 Recyclable.CollectionsTests/MathUtilsTests.cs | 63 +++++++++++++++++--
 2 files changed, 62 insertions(+), 8 deletions(-)

diff --git a/Recyclable.Collections/MathUtils.cs b/Recyclable.Collections/MathUtils.cs
index 98b63c0..40f2141 100644
--- a/Recyclable.Collections/MathUtils.cs
+++ b/Recyclable.Collections/MathUtils.cs
@@ -1,4 +1,5 @@
-using System.Runtime.CompilerServices;
+using System.Numerics;
+using System.Runtime.CompilerServices;
 
 namespace Recyclable.Collections
 {
@@ -13,10 +14,10 @@ namespace Recyclable.Collections
 		};
 
 		[MethodImpl(MethodImplOptions.AggressiveInlining)]
-		public static bool IsPow2(int value) => Array.BinarySearch(Pow2, value) >= 0;
+		public static bool IsPow2(long value) => (value != 0) && ((value & (value - 1)) == 0);
 
 		[MethodImpl(MethodImplOptions.AggressiveInlining)]
-		public static int GetPow2Shift(int value) => Array.BinarySearch(Pow2, value);
+		public static int GetPow2Shift(long value) => BitOperations.IsPow2(value) ? 63 - BitOperations.LeadingZeroCount((ulong)value) : -1;
 
 		[MethodImpl(MethodImplOptions.AggressiveInlining)]
 		public static long DivMod(long number, int divider, out long remainder)
diff --git a/Recyclable.CollectionsTests/MathUtilsTests.cs b/Recyclable.CollectionsTests/MathUtilsTests.cs
index 40c9362..dd8e625 100644
--- a/Recyclable.CollectionsTests/MathUtilsTests.cs
+++ b/Recyclable.CollectionsTests/MathUtilsTests.cs
@@ -1,10 +1,5 @@
 using FluentAssertions;
 using Recyclable.Collections;
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Text;
-using System.Threading.Tasks;
 
 namespace Recyclable.CollectionsTests
 {
@@ -28,5 +23,63 @@ namespace Recyclable.CollectionsTests
 				_ = actualRemainder.Should().Be(expectedRemainder);
 			}
 		}
+
+		[Theory]
+		[InlineData(0, false)]
+		[InlineData(1, true)]
+		[InlineData(2, true)]
+		[InlineData(3, false)]
+		[InlineData(4, true)]
+		[InlineData(5, false)]
+		[InlineData(8, true)]
+		[InlineData(16, true)]
+		[InlineData(20, false)]
+		[InlineData(32, true)]
+		[InlineData(64, true)]
+		[InlineData(128, true)]
+		[InlineData(256, true)]
+		[InlineData(512, true)]
+		[InlineData(1024, true)]
+		[InlineData(2048, true)]
+		[InlineData(4096, true)]
+		[InlineData(8192, true)]
+		[InlineData(16384, true)]
+		[InlineData(32768, true)]
+		[InlineData(65536, true)]
+		[InlineData(131072, true)]
+		[InlineData(262144, true)]
+		[InlineData(524288, true)]
+		[InlineData(1048576, true)]
+		[InlineData(2097152, true)]
+		[InlineData(4194304, true)]
+		[InlineData(8388608, true)]
+		[InlineData(16777216, true)]
+		[InlineData(33554432, true)]
+		[InlineData(67108864, true)]
+		[InlineData(134217728, true)]
+		[InlineData(268435456, true)]
+		[InlineData(536870912, true)]
+		[InlineData(1073741824, true)]
+		[InlineData(2147483648, true)]
+		[InlineData(2147483649, false)]
+		[InlineData(4294967296, true)]
+		public void IsPow2(long testNumber, bool expected)
+		{
+			_ = MathUtils.IsPow2(testNumber).Should().Be(expected);
+		}
+
+		[Theory]
+		[InlineData(-2, -1)]
+		[InlineData(-1, -1)]
+		[InlineData(0, -1)]
+		[InlineData(1, 0)]
+		[InlineData(2, 1)]
+		[InlineData(3, -1)]
+		[InlineData(4, 2)]
+		[InlineData(8, 3)]
+		public void GetPow2Shift(long testNumber, int expected)
+		{
+			_ = MathUtils.GetPow2Shift(testNumber).Should().Be(expected);
+		}
 	}
 }