Bits.cs source code in C# .NET

Source code for the .NET framework in C#

                        
Code:

                         / FX-1434 / FX-1434 / 1.0 / 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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