BitReverse

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Readme.md

General

Swap bit between MSB and LSB

Lisence

Original code is from https://ja.stackoverflow.com/a/9239/882 . CC BY-SA 3.0

BitReverse.cs

using System;

namespace BitReverse
{
    /// <summary>
    /// Swap MSB and LSB
    /// </summary>
    public static class BitReverse
    {

        /// <summary>
        /// Swap MSB and LSB
        /// </summary>
        /// <param name="input">input number</param>
        /// <returns>Swapped input number</returns>
        public static ulong UInt64(ulong input)
        {
            return ReverseBit(input, 64);
        }
        /// <summary>
        /// Swap MSB and LSB
        /// </summary>
        /// <param name="input">input number</param>
        /// <returns>Swapped input number</returns>
        public static uint UInt32(uint input)
        {
            return (uint)ReverseBit(input, 32);
        }
        /// <summary>
        /// Swap MSB and LSB
        /// </summary>
        /// <param name="input">input number</param>
        /// <returns>Swapped input number</returns>
        public static ushort UInt16(ushort input)
        {
            return (ushort)ReverseBit(input, 16);
        }
        /// <summary>
        /// Swap MSB and LSB
        /// </summary>
        /// <param name="input">input number</param>
        /// <returns>Swapped input number</returns>
        public static byte UInt8(byte input)
        {
            return (byte)ReverseBit(input, 8);
        }

        /// <summary>
        /// Swap MSB and LSB
        /// </summary>
        /// <param name="input">input number</param>
        /// <param name="bit">size of bits</param>
        /// <returns>Swapped input number</returns>
        /// <remarks>
        /// Original code is from https://ja.stackoverflow.com/a/9239/882
        /// </remarks>
        private static ulong ReverseBit(ulong input, int bit)
        {
            ulong swap = input;
            switch (bit)
            {
                case 64:
                    swap = ((swap & 0x00000000ffffffff) << 32) | ((swap >> 32) & 0x00000000ffffffff);
                    goto case 32;
                case 32:
                    swap = ((swap & 0x0000ffff0000ffff) << 16) | ((swap >> 16) & 0x0000ffff0000ffff);
                    goto case 16;
                case 16:
                    swap = ((swap & 0x00ff00ff00ff00ff) << 8) | ((swap >> 8) & 0x00ff00ff00ff00ff);
                    goto case 8;
                case 8:
                    swap = ((swap & 0x0f0f0f0f0f0f0f0f) << 4) | ((swap >> 4) & 0x0f0f0f0f0f0f0f0f);
                    goto case 4;
                case 4:
                    swap = ((swap & 0x3333333333333333) << 2) | ((swap >> 2) & 0x3333333333333333);
                    goto case 2;
                case 2:
                    swap = ((swap & 0x5555555555555555) << 1) | ((swap >> 1) & 0x5555555555555555);
                    break;
                default:
                    throw new ArgumentException("bit is out of range: 2/4/8/16/32/64", nameof(bit));
            }
            return swap;
        }
    }
}

BitReverse.csproj

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <TargetFramework>netcoreapp3.1</TargetFramework>

    <IsPackable>false</IsPackable>

    <EnableNETAnalyzers>true</EnableNETAnalyzers>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.5.0" />
    <PackageReference Include="MSTest.TestAdapter" Version="2.1.0" />
    <PackageReference Include="MSTest.TestFramework" Version="2.1.0" />
    <PackageReference Include="coverlet.collector" Version="1.2.0" />
  </ItemGroup>

</Project>

BitReverse.sln


Microsoft Visual Studio Solution File, Format Version 12.00
# Visual Studio Version 16
VisualStudioVersion = 16.0.31004.235
MinimumVisualStudioVersion = 10.0.40219.1
Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "BitReverse", "BitReverse.csproj", "{EA5230BD-3AA0-4876-88B4-31F0607EA287}"
EndProject
Global
	GlobalSection(SolutionConfigurationPlatforms) = preSolution
		Debug|Any CPU = Debug|Any CPU
		Release|Any CPU = Release|Any CPU
	EndGlobalSection
	GlobalSection(ProjectConfigurationPlatforms) = postSolution
		{EA5230BD-3AA0-4876-88B4-31F0607EA287}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
		{EA5230BD-3AA0-4876-88B4-31F0607EA287}.Debug|Any CPU.Build.0 = Debug|Any CPU
		{EA5230BD-3AA0-4876-88B4-31F0607EA287}.Release|Any CPU.ActiveCfg = Release|Any CPU
		{EA5230BD-3AA0-4876-88B4-31F0607EA287}.Release|Any CPU.Build.0 = Release|Any CPU
	EndGlobalSection
	GlobalSection(SolutionProperties) = preSolution
		HideSolutionNode = FALSE
	EndGlobalSection
	GlobalSection(ExtensibilityGlobals) = postSolution
		SolutionGuid = {2DB039F7-39F9-437E-A189-BBF37BB48600}
	EndGlobalSection
EndGlobal

BitReverseLoop.cs

using System;
using System.Security.Cryptography.X509Certificates;

namespace BitReverse
{
    /// <summary>
    /// Swap MSB and LSB
    /// </summary>
    public static class BitReverseLoop
    {

        /// <summary>
        /// Swap MSB and LSB
        /// </summary>
        /// <param name="input">input number</param>
        /// <returns>Swapped input number</returns>
        public static ulong UInt64(ulong input)
        {
            return ReverseBit(input, 64);
        }
        /// <summary>
        /// Swap MSB and LSB
        /// </summary>
        /// <param name="input">input number</param>
        /// <returns>Swapped input number</returns>
        public static uint UInt32(uint input)
        {
            return (uint)ReverseBit(input, 32);
        }
        /// <summary>
        /// Swap MSB and LSB
        /// </summary>
        /// <param name="input">input number</param>
        /// <returns>Swapped input number</returns>
        public static ushort UInt16(ushort input)
        {
            return (ushort)ReverseBit(input, 16);
        }
        /// <summary>
        /// Swap MSB and LSB
        /// </summary>
        /// <param name="input">input number</param>
        /// <returns>Swapped input number</returns>
        public static byte UInt8(byte input)
        {
            return (byte)ReverseBit(input, 8);
        }

        /// <summary>
        /// Swap MSB and LSB
        /// </summary>
        /// <param name="input">input number</param>
        /// <param name="bit">size of bits</param>
        /// <returns>Swapped input number</returns>
        /// <remarks>
        /// Original code is from https://ja.stackoverflow.com/a/7500/882
        /// </remarks>
        private static ulong ReverseBit(ulong input, int bit)
        {
            ulong swap = 0;
            while(bit-- > 0)
            {
                swap <<= 1;
                swap |= (input & 1u);
                input >>= 1;
            }
            return swap;
        }
    }
}

BitReverseTest.cs

#define BITREVERSE
#define BITREVERSELOOP
using Microsoft.VisualStudio.TestTools.UnitTesting;
using System;
using System.Diagnostics;
using System.Linq;

namespace BitReverse
{
    [TestClass]
    public class BitReverseTest
    {
        [TestMethod]
        public void TestUnit64()
        {
            ulong input = 0x0000000000000001u;
            ulong result;
#if BITREVERSE
            result = BitReverse.UInt64(input);
            Assert.AreEqual(0x8000000000000000uL, result);
#endif
#if BITREVERSELOOP
            result = BitReverseLoop.UInt64(input);
            Assert.AreEqual(0x8000000000000000uL, result);
#endif
        }
        [TestMethod]
        public void TestUnit32()
        {
            uint input = 0x00000001u;
            uint result;
#if BITREVERSE
            result = BitReverse.UInt32(input);
            Assert.AreEqual(0x80000000u, result);
#endif
#if BITREVERSELOOP
            result = BitReverseLoop.UInt32(input);
            Assert.AreEqual(0x80000000u, result);
#endif
        }
        [TestMethod]
        public void TestUnit16()
        {
            ushort input = (ushort)0x0001u;
            ushort result;
#if BITREVERSE
            result = BitReverse.UInt16(input);
            Assert.AreEqual(0x8000u, result);
#endif
#if BITREVERSELOOP
            result = BitReverseLoop.UInt16(input);
            Assert.AreEqual(0x8000u, result);
#endif
        }
        [TestMethod]
        public void TestUnit8()
        {
            byte input = (byte)0x01u;
            byte result;
#if BITREVERSE
            result = BitReverse.UInt8(input);
            Assert.AreEqual(0x80u, result);
#endif
#if BITREVERSELOOP
#endif
        }



        [TestMethod]
        public void TestSpeed64()
        {
            var sw = new Stopwatch();
            var rand = new Random(0x1234);
            var testData = Enumerable.Range(1, 100000).Select((w, i) => new
            {
#pragma warning disable CS0675
                Value = (ulong)((((ulong)rand.Next()) << 32) | (ulong)rand.Next()),
#pragma warning restore CS0675
                Index = i,
            }).ToArray();
#if BITREVERSE
            var result = new ulong[testData.Length];

            sw.Start();

            foreach (var item in testData)
            {
                result[item.Index] = BitReverse.UInt64(item.Value);
            }
            var lap = sw.ElapsedMilliseconds;
            sw.Stop();

            Console.WriteLine("Test ran {1} items in {0}ms", lap, testData.Length);

            sw.Reset();
#endif
#if BITREVERSELOOP
            var resultLoop = new ulong[testData.Length];
            sw.Start();

            foreach (var item in testData)
            {
                resultLoop[item.Index] = BitReverseLoop.UInt64(item.Value);
            }
            var lapLoop = sw.ElapsedMilliseconds;
            sw.Stop();
            Console.WriteLine("Test ran loop {1} items in {0}ms", lapLoop, testData.Length);
#endif
#if BITREVERSE
            foreach (var item in testData)
            {
                Console.WriteLine("{0,0:X8} ¨ {1,0:X8}", item.Value, result[item.Index]);
            }
#endif

            sw.Reset();
        }
    }
}