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