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//------------------------------------------------------------------------------
// <copyright file="Bits.cs" company="Microsoft">
// Copyright (c) Microsoft Corporation. All rights reserved.
// </copyright>
// <owner current="true" primary="true">[....]</owner>
//------------------------------------------------------------------------------
namespace System.Xml {
using System;
using System.Diagnostics;
/// <summary>
/// Contains static utility methods used to manipulate bits in a word.
/// </summary>
internal static class Bits {
private static readonly uint MASK_0101010101010101 = 0x55555555;
private static readonly uint MASK_0011001100110011 = 0x33333333;
private static readonly uint MASK_0000111100001111 = 0x0f0f0f0f;
private static readonly uint MASK_0000000011111111 = 0x00ff00ff;
private static readonly uint MASK_1111111111111111 = 0x0000ffff;
/// <summary>
/// Returns the number of 1 bits in an unsigned integer. Counts bits by divide-and-conquer method,
/// first computing 16 2-bit counts, then 8 4-bit counts, then 4 8-bit counts, then 2 16-bit counts,
/// and finally 1 32-bit count.
/// </summary>
public static int Count(uint num) {
num = (num & MASK_0101010101010101) + ((num >> 1) & MASK_0101010101010101);
num = (num & MASK_0011001100110011) + ((num >> 2) & MASK_0011001100110011);
num = (num & MASK_0000111100001111) + ((num >> 4) & MASK_0000111100001111);
num = (num & MASK_0000000011111111) + ((num >> 8) & MASK_0000000011111111);
num = (num & MASK_1111111111111111) + (num >> 16);
return (int) num;
}
/// <summary>
/// Returns true if the unsigned integer has exactly one bit set.
/// </summary>
public static bool ExactlyOne(uint num) {
return num != 0 && (num & (num - 1)) == 0;
}
#if !SILVERLIGHT // These methods are not used in Silverlight
/// <summary>
/// Returns true if the unsigned integer has more than one bit set.
/// </summary>
public static bool MoreThanOne(uint num) {
return (num & (num - 1)) != 0;
}
/// <summary>
/// Clear the least significant bit that is set and return the result.
/// </summary>
public static uint ClearLeast(uint num) {
return num & (num - 1);
}
#endif
/// <summary>
/// Compute the 1-based position of the least sigificant bit that is set, and return it (return 0 if no bits are set).
/// (e.g. 0x1001100 will return 3, since the 3rd bit is set).
/// </summary>
public static int LeastPosition(uint num) {
if (num == 0) return 0;
return Count(num ^ (num - 1));
}
}
}
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