Code:
/ DotNET / DotNET / 8.0 / untmp / whidbey / REDBITS / ndp / fx / src / Xml / System / Xml / Bits.cs / 1 / Bits.cs
//------------------------------------------------------------------------------ //// Copyright (c) Microsoft Corporation. All rights reserved. // //[....] //----------------------------------------------------------------------------- namespace System.Xml { using System; using System.Diagnostics; ////// Contains static utility methods used to manipulate bits in a word. /// 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; ////// 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. /// 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; } ////// Returns true if the unsigned integer has exactly one bit set. /// public static bool ExactlyOne(uint num) { return num != 0 && (num & (num - 1)) == 0; } ////// Returns true if the unsigned integer has more than one bit set. /// public static bool MoreThanOne(uint num) { return (num & (num - 1)) != 0; } ////// Clear the least significant bit that is set and return the result. /// public static uint ClearLeast(uint num) { return num & (num - 1); } ////// 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). /// public static int LeastPosition(uint num) { if (num == 0) return 0; return Count(num ^ (num - 1)); } } } // File provided for Reference Use Only by Microsoft Corporation (c) 2007. // Copyright (c) Microsoft Corporation. All rights reserved.
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