BitHelper.cs source code in C# .NET

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                         / 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / ndp / fx / src / CompMod / System / Collections / Generic / BitHelper.cs / 1305376 / BitHelper.cs
                        
                        
                            using System; 
using System.Collections;
using System.Text;

namespace System.Collections.Generic { 

    ///  
    /// ABOUT: 
    /// Helps with operations that rely on bit marking to indicate whether an item in the
    /// collection should be added, removed, visited already, etc. 
    ///
    /// BitHelper doesn't allocate the array; you must pass in an array or ints allocated on the
    /// stack or heap. ToIntArrayLength() tells you the int array size you must allocate.
    /// 
    /// USAGE:
    /// Suppose you need to represent a bit array of length (i.e. logical bit array length) 
    /// BIT_ARRAY_LENGTH. Then this is the suggested way to instantiate BitHelper: 
    /// ****************************************************************************
    /// int intArrayLength = BitHelper.ToIntArrayLength(BIT_ARRAY_LENGTH); 
    /// BitHelper bitHelper;
    /// if (intArrayLength less than stack alloc threshold)
    ///     int* m_arrayPtr = stackalloc int[intArrayLength];
    ///     bitHelper = new BitHelper(m_arrayPtr, intArrayLength); 
    /// else
    ///     int[] m_arrayPtr = new int[intArrayLength]; 
    ///     bitHelper = new BitHelper(m_arrayPtr, intArrayLength); 
    /// ***************************************************************************
    /// 
    /// IMPORTANT:
    /// The second ctor args, length, should be specified as the length of the int array, not
    /// the logical bit array. Because length is used for bounds checking into the int array,
    /// it's especially important to get this correct for the stackalloc version. See the code 
    /// samples above; this is the value gotten from ToIntArrayLength().
    /// 
    /// The length ctor argument is the only exception; for other methods -- MarkBit and 
    /// IsMarked -- pass in values as indices into the logical bit array, and it will be mapped
    /// to the position within the array of ints. 
    ///
    ///

 

 
    unsafe internal class BitHelper {   // should not be serialized 

        private const byte MarkedBitFlag = 1; 
        private const byte IntSize = 32;

        // m_length of underlying int array (not logical bit array)
        private int m_length; 

        // ptr to stack alloc'd array of ints 
        private int* m_arrayPtr; 

        // array of ints 
        private int[] m_array;

        // whether to operate on stack alloc'd or heap alloc'd array
        private bool useStackAlloc; 

        ///  
        /// Instantiates a BitHelper with a heap alloc'd array of ints 
        /// 
        /// int array to hold bits 
        /// length of int array
        // 
        // 
        //  
        // 
        [System.Security.SecurityCritical] 
        internal BitHelper(int* bitArrayPtr, int length) { 
            this.m_arrayPtr = bitArrayPtr;
            this.m_length = length; 
            useStackAlloc = true;
        }

        ///  
        /// Instantiates a BitHelper with a heap alloc'd array of ints
        ///  
        /// int array to hold bits 
        /// length of int array
        internal BitHelper(int[] bitArray, int length) { 
            this.m_array = bitArray;
            this.m_length = length;
        }
 
        /// 
        /// Mark bit at specified position 
        ///  
        /// 
        //  
        // 
        // 
        [System.Security.SecurityCritical]
        internal unsafe void MarkBit(int bitPosition) { 
            if (useStackAlloc) {
                int bitArrayIndex = bitPosition / IntSize; 
                if (bitArrayIndex < m_length && bitArrayIndex >= 0) { 
                    m_arrayPtr[bitArrayIndex] |= (MarkedBitFlag << (bitPosition % IntSize));
                } 
            }
            else {
                int bitArrayIndex = bitPosition / IntSize;
                if (bitArrayIndex < m_length && bitArrayIndex >= 0) { 
                    m_array[bitArrayIndex] |= (MarkedBitFlag << (bitPosition % IntSize));
                } 
            } 
        }
 
        /// 
        /// Is bit at specified position marked?
        /// 
        ///  
        /// 
        //  
        //  
        // 
        [System.Security.SecurityCritical] 
        internal unsafe bool IsMarked(int bitPosition) {
            if (useStackAlloc) {
                int bitArrayIndex = bitPosition / IntSize;
                if (bitArrayIndex < m_length && bitArrayIndex >= 0) { 
                    return ((m_arrayPtr[bitArrayIndex] & (MarkedBitFlag << (bitPosition % IntSize))) != 0);
                } 
                return false; 
            }
            else { 
                int bitArrayIndex = bitPosition / IntSize;
                if (bitArrayIndex < m_length && bitArrayIndex >= 0) {
                    return ((m_array[bitArrayIndex] & (MarkedBitFlag << (bitPosition % IntSize))) != 0);
                } 
                return false;
            } 
        } 

        ///  
        /// How many ints must be allocated to represent n bits. Returns (n+31)/32, but
        /// avoids overflow
        /// 
        ///  
        /// 
        internal static int ToIntArrayLength(int n) { 
            return n > 0 ? ((n - 1) / IntSize + 1) : 0; 
        }
 
    }
}

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
// Copyright (c) Microsoft Corporation. All rights reserved.
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BitHelper.cs source code in C# .NET

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