path: root/src/mscorlib/src/System/Collections/BitArray.cs

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.

/*=============================================================================
**
**
** 
**
**
** Purpose: The BitArray class manages a compact array of bit values.
**
**
=============================================================================*/
namespace System.Collections {

    using System;
    using System.Security.Permissions;
    using System.Diagnostics.Contracts;
    // A vector of bits.  Use this to store bits efficiently, without having to do bit 
    // shifting yourself.
[System.Runtime.InteropServices.ComVisible(true)]
    [Serializable()] public sealed class BitArray : ICollection, ICloneable {
        private BitArray() {
        }

        /*=========================================================================
        ** Allocates space to hold length bit values. All of the values in the bit
        ** array are set to false.
        **
        ** Exceptions: ArgumentException if length < 0.
        =========================================================================*/
        public BitArray(int length) 
            : this(length, false) {
        }
    
        /*=========================================================================
        ** Allocates space to hold length bit values. All of the values in the bit
        ** array are set to defaultValue.
        **
        ** Exceptions: ArgumentOutOfRangeException if length < 0.
        =========================================================================*/
        public BitArray(int length, bool defaultValue) {
            if (length < 0) {
                throw new ArgumentOutOfRangeException(nameof(length), Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
            }
            Contract.EndContractBlock();
    
            m_array = new int[GetArrayLength(length, BitsPerInt32)];
            m_length = length;
    
            int fillValue = defaultValue ? unchecked(((int)0xffffffff)) : 0;
            for (int i = 0; i < m_array.Length; i++) {
                m_array[i] = fillValue;
            }

            _version = 0;
        }
    
        /*=========================================================================
        ** Allocates space to hold the bit values in bytes. bytes[0] represents
        ** bits 0 - 7, bytes[1] represents bits 8 - 15, etc. The LSB of each byte
        ** represents the lowest index value; bytes[0] & 1 represents bit 0,
        ** bytes[0] & 2 represents bit 1, bytes[0] & 4 represents bit 2, etc.
        **
        ** Exceptions: ArgumentException if bytes == null.
        =========================================================================*/
        public BitArray(byte[] bytes) {
            if (bytes == null) {
                throw new ArgumentNullException(nameof(bytes));
            }
            Contract.EndContractBlock();
            // this value is chosen to prevent overflow when computing m_length.
            // m_length is of type int32 and is exposed as a property, so 
            // type of m_length can't be changed to accommodate.
            if (bytes.Length > Int32.MaxValue / BitsPerByte) {
                throw new ArgumentException(Environment.GetResourceString("Argument_ArrayTooLarge", BitsPerByte), nameof(bytes));
            }
    
            m_array = new int[GetArrayLength(bytes.Length, BytesPerInt32)];
            m_length = bytes.Length * BitsPerByte;
    
            int i = 0;
            int j = 0;
            while (bytes.Length - j >= 4) {
                m_array[i++] = (bytes[j] & 0xff) |
                              ((bytes[j + 1] & 0xff) << 8) |
                              ((bytes[j + 2] & 0xff) << 16) |
                              ((bytes[j + 3] & 0xff) << 24);
                j += 4;
            }
    
            Contract.Assert(bytes.Length - j >= 0, "BitArray byteLength problem");
            Contract.Assert(bytes.Length - j < 4, "BitArray byteLength problem #2");
    
            switch (bytes.Length - j) {
                case 3:
                    m_array[i] = ((bytes[j + 2] & 0xff) << 16);
                    goto case 2;
                    // fall through
                case 2:
                    m_array[i] |= ((bytes[j + 1] & 0xff) << 8);
                    goto case 1;
                    // fall through
                case 1:
                    m_array[i] |= (bytes[j] & 0xff);
            break;
            }

            _version = 0;
        }

        public BitArray(bool[] values) {
            if (values == null) {
                throw new ArgumentNullException(nameof(values));
            }
            Contract.EndContractBlock();
    
            m_array = new int[GetArrayLength(values.Length, BitsPerInt32)];
            m_length = values.Length;
    
            for (int i = 0;i<values.Length;i++) {
                if (values[i])
                    m_array[i/32] |= (1 << (i%32));
            }

            _version = 0;

        }
    
        /*=========================================================================
        ** Allocates space to hold the bit values in values. values[0] represents
        ** bits 0 - 31, values[1] represents bits 32 - 63, etc. The LSB of each
        ** integer represents the lowest index value; values[0] & 1 represents bit
        ** 0, values[0] & 2 represents bit 1, values[0] & 4 represents bit 2, etc.
        **
        ** Exceptions: ArgumentException if values == null.
        =========================================================================*/
        public BitArray(int[] values) {
            if (values == null) {
                throw new ArgumentNullException(nameof(values));
            }
            Contract.EndContractBlock();
            // this value is chosen to prevent overflow when computing m_length
            if (values.Length > Int32.MaxValue / BitsPerInt32) {
                throw new ArgumentException(Environment.GetResourceString("Argument_ArrayTooLarge", BitsPerInt32), nameof(values));
            }
    
            m_array = new int[values.Length];
            m_length = values.Length * BitsPerInt32;
    
            Array.Copy(values, m_array, values.Length);

            _version = 0;
        }
    
        /*=========================================================================
        ** Allocates a new BitArray with the same length and bit values as bits.
        **
        ** Exceptions: ArgumentException if bits == null.
        =========================================================================*/
        public BitArray(BitArray bits) {
            if (bits == null) {
                throw new ArgumentNullException(nameof(bits));
            }
            Contract.EndContractBlock();
    
            int arrayLength = GetArrayLength(bits.m_length, BitsPerInt32);
            m_array = new int[arrayLength];
            m_length = bits.m_length;
    
            Array.Copy(bits.m_array, m_array, arrayLength);

            _version = bits._version;
        }

        public bool this[int index] {
                get {
                    return Get(index);
                }
                set {
                    Set(index,value);
                }
         }
    
        /*=========================================================================
        ** Returns the bit value at position index.
        **
        ** Exceptions: ArgumentOutOfRangeException if index < 0 or
        **             index >= GetLength().
        =========================================================================*/
        public bool Get(int index) {
            if (index < 0 || index >= Length) {
                throw new ArgumentOutOfRangeException(nameof(index), Environment.GetResourceString("ArgumentOutOfRange_Index"));
            }
            Contract.EndContractBlock();
    
            return (m_array[index / 32] & (1 << (index % 32))) != 0;
        }
    
        /*=========================================================================
        ** Sets the bit value at position index to value.
        **
        ** Exceptions: ArgumentOutOfRangeException if index < 0 or
        **             index >= GetLength().
        =========================================================================*/
        public void Set(int index, bool value) {
            if (index < 0 || index >= Length) {
                throw new ArgumentOutOfRangeException(nameof(index), Environment.GetResourceString("ArgumentOutOfRange_Index"));
            }
            Contract.EndContractBlock();
    
            if (value) {
                m_array[index / 32] |= (1 << (index % 32));
            } else {
                m_array[index / 32] &= ~(1 << (index % 32));
            }

            _version++;
        }
    
        /*=========================================================================
        ** Sets all the bit values to value.
        =========================================================================*/
        public void SetAll(bool value) {
            int fillValue = value ? unchecked(((int)0xffffffff)) : 0;
            int ints = GetArrayLength(m_length, BitsPerInt32);
            for (int i = 0; i < ints; i++) {
                m_array[i] = fillValue;
            }

            _version++;
        }
    
        /*=========================================================================
        ** Returns a reference to the current instance ANDed with value.
        **
        ** Exceptions: ArgumentException if value == null or
        **             value.Length != this.Length.
        =========================================================================*/
        public BitArray And(BitArray value) {
            if (value==null)
                throw new ArgumentNullException(nameof(value));
            if (Length != value.Length)
                throw new ArgumentException(Environment.GetResourceString("Arg_ArrayLengthsDiffer"));
            Contract.EndContractBlock();
    
            int ints = GetArrayLength(m_length, BitsPerInt32);
            for (int i = 0; i < ints; i++) {
                m_array[i] &= value.m_array[i];
            }
    
            _version++;
            return this;
        }
    
        /*=========================================================================
        ** Returns a reference to the current instance ORed with value.
        **
        ** Exceptions: ArgumentException if value == null or
        **             value.Length != this.Length.
        =========================================================================*/
        public BitArray Or(BitArray value) {
            if (value==null)
                throw new ArgumentNullException(nameof(value));
            if (Length != value.Length)
                throw new ArgumentException(Environment.GetResourceString("Arg_ArrayLengthsDiffer"));
            Contract.EndContractBlock();
    
            int ints = GetArrayLength(m_length, BitsPerInt32);
            for (int i = 0; i < ints; i++) {
                m_array[i] |= value.m_array[i];
            }
    
            _version++;
            return this;
        }
    
        /*=========================================================================
        ** Returns a reference to the current instance XORed with value.
        **
        ** Exceptions: ArgumentException if value == null or
        **             value.Length != this.Length.
        =========================================================================*/
        public BitArray Xor(BitArray value) {
            if (value==null)
                throw new ArgumentNullException(nameof(value));
            if (Length != value.Length)
                throw new ArgumentException(Environment.GetResourceString("Arg_ArrayLengthsDiffer"));
            Contract.EndContractBlock();
    
            int ints = GetArrayLength(m_length, BitsPerInt32);
            for (int i = 0; i < ints; i++) {
                m_array[i] ^= value.m_array[i];
            }
            
            _version++;
            return this;
        }
    
        /*=========================================================================
        ** Inverts all the bit values. On/true bit values are converted to
        ** off/false. Off/false bit values are turned on/true. The current instance
        ** is updated and returned.
        =========================================================================*/
        public BitArray Not() {
            int ints = GetArrayLength(m_length, BitsPerInt32);
            for (int i = 0; i < ints; i++) {
                m_array[i] = ~m_array[i];
            }
    
            _version++;
            return this;
        }

        public int Length {
            get {
                Contract.Ensures(Contract.Result<int>() >= 0);
                return m_length;
            }
            set {
                if (value < 0) {
                    throw new ArgumentOutOfRangeException(nameof(value), Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
                }
                Contract.EndContractBlock();

                int newints = GetArrayLength(value, BitsPerInt32);
                if (newints > m_array.Length || newints + _ShrinkThreshold < m_array.Length) {
                    // grow or shrink (if wasting more than _ShrinkThreshold ints)
                    int[] newarray = new int[newints];
                    Array.Copy(m_array, newarray, newints > m_array.Length ? m_array.Length : newints);
                    m_array = newarray;
                }
                
                if (value > m_length) {
                    // clear high bit values in the last int
                    int last = GetArrayLength(m_length, BitsPerInt32) - 1;
                    int bits = m_length % 32;
                    if (bits > 0) {
                        m_array[last] &= (1 << bits) - 1;
                    }
                    
                    // clear remaining int values
                    Array.Clear(m_array, last + 1, newints - last - 1);
                }
                
                m_length = value;
                _version++;
            }
        }

        // ICollection implementation
        public void CopyTo(Array array, int index)
        {
            if (array == null)
                throw new ArgumentNullException(nameof(array));

            if (index < 0)
                throw new ArgumentOutOfRangeException(nameof(index), Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));

            if (array.Rank != 1)
                throw new ArgumentException(Environment.GetResourceString("Arg_RankMultiDimNotSupported"), nameof(array));
                
            Contract.EndContractBlock();

            if (array is int[])
            {
                Array.Copy(m_array, 0, array, index, GetArrayLength(m_length, BitsPerInt32));
            }
            else if (array is byte[])
            {
                int arrayLength = GetArrayLength(m_length, BitsPerByte);
                if ((array.Length - index) < arrayLength)
                     throw new ArgumentException(Environment.GetResourceString("Argument_InvalidOffLen"));

                byte [] b = (byte[])array;
                for (int i = 0; i < arrayLength; i++)
                    b[index + i] = (byte)((m_array[i/4] >> ((i%4)*8)) & 0x000000FF); // Shift to bring the required byte to LSB, then mask
            }
            else if (array is bool[])
            {
                if (array.Length - index < m_length)
                     throw new ArgumentException(Environment.GetResourceString("Argument_InvalidOffLen"));

                bool [] b = (bool[])array;
                for (int i = 0;i<m_length;i++)
                    b[index + i] = ((m_array[i/32] >> (i%32)) & 0x00000001) != 0;
            }
            else
                throw new ArgumentException(Environment.GetResourceString("Arg_BitArrayTypeUnsupported"), nameof(array));
        }
        
        public int Count
        { 
            get
            {
                Contract.Ensures(Contract.Result<int>() >= 0);

                return m_length;
            }
        }

        public Object Clone()
        {
            Contract.Ensures(Contract.Result<Object>() != null);
            Contract.Ensures(((BitArray)Contract.Result<Object>()).Length == this.Length);

            return new BitArray(this);
        }
        
        public Object SyncRoot
        {
             get
             {
                if( _syncRoot == null) {
                    System.Threading.Interlocked.CompareExchange<Object>(ref _syncRoot, new Object(), null);    
                }
                return _syncRoot; 
             }
        }
    
        public bool IsReadOnly 
        { 
            get
            {
                return false;
            }
        }

        public bool IsSynchronized
        { 
            get
            {
                return false;
            }
        }

        public IEnumerator GetEnumerator()
        {
            return new BitArrayEnumeratorSimple(this);
        }

        // XPerY=n means that n Xs can be stored in 1 Y. 
        private const int BitsPerInt32 = 32;
        private const int BytesPerInt32 = 4;
        private const int BitsPerByte = 8;

        /// <summary>
        /// Used for conversion between different representations of bit array. 
        /// Returns (n+(div-1))/div, rearranged to avoid arithmetic overflow. 
        /// For example, in the bit to int case, the straightforward calc would 
        /// be (n+31)/32, but that would cause overflow. So instead it's 
        /// rearranged to ((n-1)/32) + 1, with special casing for 0.
        /// 
        /// Usage:
        /// GetArrayLength(77, BitsPerInt32): returns how many ints must be 
        /// allocated to store 77 bits.
        /// </summary>
        /// <param name="n"></param>
        /// <param name="div">use a conversion constant, e.g. BytesPerInt32 to get
        /// how many ints are required to store n bytes</param>
        /// <returns></returns>
        private static int GetArrayLength(int n, int div) {
            Contract.Assert(div > 0, "GetArrayLength: div arg must be greater than 0");
            return n > 0 ? (((n - 1) / div) + 1) : 0;
        }

        [Serializable]
        private class BitArrayEnumeratorSimple : IEnumerator, ICloneable
        {
            private BitArray bitarray;
            private int index;
            private int version;
            private bool currentElement;
               
            internal BitArrayEnumeratorSimple(BitArray bitarray) {
                this.bitarray = bitarray;
                this.index = -1;
                version = bitarray._version;
            }

            public Object Clone() {
                return MemberwiseClone();
            }
                
            public virtual bool MoveNext() {
                if (version != bitarray._version) throw new InvalidOperationException(Environment.GetResourceString(ResId.InvalidOperation_EnumFailedVersion));
                if (index < (bitarray.Count-1)) {
                    index++;
                    currentElement = bitarray.Get(index);
                    return true;
                }
                else
                    index = bitarray.Count;
                
                return false;
            }
    
            public virtual Object Current {
                get {
                    if (index == -1)
                        throw new InvalidOperationException(Environment.GetResourceString(ResId.InvalidOperation_EnumNotStarted));
                    if (index >= bitarray.Count)
                        throw new InvalidOperationException(Environment.GetResourceString(ResId.InvalidOperation_EnumEnded)); 
                    return currentElement;
                }
            }
    
            public void Reset() {
                if (version != bitarray._version) throw new InvalidOperationException(Environment.GetResourceString(ResId.InvalidOperation_EnumFailedVersion));
                index = -1;
            }
        }
    
        private int[] m_array;
        private int m_length;
        private int _version;
        [NonSerialized]
        private Object _syncRoot;
    
        private const int _ShrinkThreshold = 256;
    }

}