zxing/csharp/qrcode/encoder/BitVector.cs

/*
* Copyright 2007 ZXing authors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
*      http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
using System;
using System.Text;
using com.google.zxing;
using com.google.zxing.common;

namespace com.google.zxing.qrcode.encoder
{
    public sealed class BitVector { 
    
          private int sizeInBits;
          private sbyte[] array;

          // For efficiency, start out with some room to work.
          private static int DEFAULT_SIZE_IN_BYTES = 32;

          public BitVector() {
            sizeInBits = 0;
            array = new sbyte[DEFAULT_SIZE_IN_BYTES];
          }

          // Return the bit value at "index".
          public int at(int index) {
            if (index < 0 || index >= sizeInBits) {
              throw new ArgumentException("Bad index: " + index);
            }
            int value = array[index >> 3] & 0xff;
            return (value >> (7 - (index & 0x7))) & 1;
          }

          // Return the number of bits in the bit vector.
          public int size() {
            return sizeInBits;
          }

          // Return the number of bytes in the bit vector.
          public int sizeInBytes() {
            return (sizeInBits + 7) >> 3;
          }

          // Append one bit to the bit vector.
          public void appendBit(int bit) {
            if (!(bit == 0 || bit == 1)) {
              throw new ArgumentException("Bad bit");
            }
            int numBitsInLastByte = sizeInBits & 0x7;
            // We'll expand array if we don't have bits in the last byte.
            if (numBitsInLastByte == 0) {
              appendByte(0);
              sizeInBits -= 8;
            }
            // Modify the last byte.
            array[sizeInBits >> 3] |= (sbyte)(bit << (7 - numBitsInLastByte));
            ++sizeInBits;
          }

          // Append "numBits" bits in "value" to the bit vector.
          // REQUIRES: 0<= numBits <= 32.
          //
          // Examples:
          // - appendBits(0x00, 1) adds 0.
          // - appendBits(0x00, 4) adds 0000.
          // - appendBits(0xff, 8) adds 11111111.
          public void appendBits(int value, int numBits) {
            if (numBits < 0 || numBits > 32) {
              throw new ArgumentException("Num bits must be between 0 and 32");
            }
            int numBitsLeft = numBits;
            while (numBitsLeft > 0) {
              // Optimization for byte-oriented appending.
              if ((sizeInBits & 0x7) == 0 && numBitsLeft >= 8) {
                int newByte = (value >> (numBitsLeft - 8)) & 0xff;
                appendByte(newByte);
                numBitsLeft -= 8;
              } else {
                int bit = (value >> (numBitsLeft - 1)) & 1;
                appendBit(bit);
                --numBitsLeft;
              }
            }
          }

          // Append "bits".
          public void appendBitVector(BitVector bits) {
            int size = bits.size();
            for (int i = 0; i < size; ++i) {
              appendBit(bits.at(i));
            }
          }

          // Modify the bit vector by XOR'ing with "other"
          public void xor(BitVector other) {
            if (sizeInBits != other.size()) {
              throw new ArgumentException("BitVector sizes don't match");
            }
            int sizeInBytes = (sizeInBits + 7) >> 3;
            for (int i = 0; i < sizeInBytes; ++i) {
              // The last byte could be incomplete (i.e. not have 8 bits in
              // it) but there is no problem since 0 XOR 0 == 0.
              array[i] ^= other.array[i];
            }
          }

          // Return String like "01110111" for debugging.
          public String toString() {
              StringBuilder result = new StringBuilder(sizeInBits);
            for (int i = 0; i < sizeInBits; ++i) {
              if (at(i) == 0) {
                result.Append('0');
              } else if (at(i) == 1) {
                result.Append('1');
              } else {
                throw new ArgumentException("Byte isn't 0 or 1");
              }
            }
            return result.ToString();
          }

          // Callers should not assume that array.length is the exact number of bytes needed to hold
          // sizeInBits - it will typically be larger for efficiency.
          public sbyte[] getArray() {
            return array;
          }

          // Add a new byte to the end, possibly reallocating and doubling the size of the array if we've
          // run out of room.
          private void appendByte(int value) {
            if ((sizeInBits >> 3) == array.Length) {
              sbyte[] newArray = new sbyte[(array.Length << 1)];
              System.Array.Copy (array, 0, newArray, 0, array.Length);
              array = newArray;
            }
            array[sizeInBits >> 3] = (sbyte) value;
            sizeInBits += 8;
          }
    }
}