Nuclex.Support/Source/IntegerHelper.cs

#region Apache License 2.0
/*
Nuclex .NET Framework
Copyright (C) 2002-2024 Markus Ewald / Nuclex Development Labs

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/
#endregion // Apache License 2.0

using System;

namespace Nuclex.Support {

  /// <summary>Helper methods for working with integer types</summary>
  public static class IntegerHelper {

    /// <summary>Returns the next highest power of 2 from the specified value</summary>
    /// <param name="value">Value of which to return the next highest power of 2</param>
    /// <returns>The next highest power of 2 to the value</returns>
    public static long NextPowerOf2(this long value) {
      return (long)NextPowerOf2((ulong)value);
    }

    /// <summary>Returns the next highest power of 2 from the specified value</summary>
    /// <param name="value">Value of which to return the next highest power of 2</param>
    /// <returns>The next highest power of 2 to the value</returns>
    public static ulong NextPowerOf2(this ulong value) {
      if (value == 0)
        return 1;

      --value;
      value |= value >> 1;
      value |= value >> 2;
      value |= value >> 4;
      value |= value >> 8;
      value |= value >> 16;
      value |= value >> 32;
      ++value;

      return value;
    }

    /// <summary>Returns the next highest power of 2 from the specified value</summary>
    /// <param name="value">Value of which to return the next highest power of 2</param>
    /// <returns>The next highest power of 2 to the value</returns>
    public static int NextPowerOf2(this int value) {
      return (int)NextPowerOf2((uint)value);
    }

    /// <summary>Returns the next highest power of 2 from the specified value</summary>
    /// <param name="value">Value of which to return the next highest power of 2</param>
    /// <returns>The next highest power of 2 to the value</returns>
    public static uint NextPowerOf2(this uint value) {
      if (value == 0)
        return 1;

      --value;
      value |= value >> 1;
      value |= value >> 2;
      value |= value >> 4;
      value |= value >> 8;
      value |= value >> 16;
      ++value;

      return value;
    }

    /// <summary>Returns the number of bits set in an integer</summary>
    /// <param name="value">Value whose bits will be counted</param>
    /// <returns>The number of bits set in the integer</returns>
    public static int CountBits(this int value) {
      return CountBits((uint)value);
    }

    /// <summary>Returns the number of bits set in an unsigned integer</summary>
    /// <param name="value">Value whose bits will be counted</param>
    /// <returns>The number of bits set in the unsigned integer</returns>
    /// <remarks>
    ///   Based on a trick revealed here:
    ///   http://stackoverflow.com/questions/109023
    /// </remarks>
    public static int CountBits(this uint value) {
      value = value - ((value >> 1) & 0x55555555);
      value = (value & 0x33333333) + ((value >> 2) & 0x33333333);

      return (int)unchecked(
        ((value + (value >> 4) & 0xF0F0F0F) * 0x1010101) >> 24
      );
    }

    /// <summary>Returns the number of bits set in a long integer</summary>
    /// <param name="value">Value whose bits will be counted</param>
    /// <returns>The number of bits set in the long integer</returns>
    public static int CountBits(this long value) {
      return CountBits((ulong)value);
    }

    /// <summary>Returns the number of bits set in an unsigned long integer</summary>
    /// <param name="value">Value whose bits will be counted</param>
    /// <returns>The number of bits set in the unsigned long integer</returns>
    /// <remarks>
    ///   Based on a trick revealed here:
    ///   http://stackoverflow.com/questions/2709430
    /// </remarks>
    public static int CountBits(this ulong value) {
      value = value - ((value >> 1) & 0x5555555555555555UL);
      value = (value & 0x3333333333333333UL) + ((value >> 2) & 0x3333333333333333UL);

      return (int)unchecked(
        (((value + (value >> 4)) & 0xF0F0F0F0F0F0F0FUL) * 0x101010101010101UL) >> 56
      );
    }

  }

} // namespace Nuclex.Support