content: /*
   * 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.
   */
  
  package com.ailiwean.core.zxing.core.common;
  
  /**
   * <p>This provides an easy abstraction to read bits at a time from a sequence of bytes, where the
   * number of bits read is not often a multiple of 8.</p>
   *
   * <p>This class is thread-safe but not reentrant -- unless the caller modifies the bytes array
   * it passed in, in which case all bets are off.</p>
   *
   * @author Sean Owen
   */
  public final class BitSource {
  
    private final byte[] bytes;
    private int byteOffset;
    private int bitOffset;
  
    /**
     * @param bytes bytes from which this will read bits. Bits will be read from the first byte first.
     * Bits are read within a byte from most-significant to least-significant bit.
     */
    public BitSource(byte[] bytes) {
      this.bytes = bytes;
    }
  
    /**
     * @return index of next bit in current byte which would be read by the next call to {@link #readBits(int)}.
     */
    public int getBitOffset() {
      return bitOffset;
    }
  
    /**
     * @return index of next byte in input byte array which would be read by the next call to {@link #readBits(int)}.
     */
    public int getByteOffset() {
      return byteOffset;
    }
  
    /**
     * @param numBits number of bits to read
     * @return int representing the bits read. The bits will appear as the least-significant
     *         bits of the int
     * @throws IllegalArgumentException if numBits isn't in [1,32] or more than is available
     */
    public int readBits(int numBits) {
      if (numBits < 1 || numBits > 32 || numBits > available()) {
        throw new IllegalArgumentException(String.valueOf(numBits));
      }
  
      int result = 0;
  
      // First, read remainder from current byte
      if (bitOffset > 0) {
        int bitsLeft = 8 - bitOffset;
        int toRead = Math.min(numBits, bitsLeft);
        int bitsToNotRead = bitsLeft - toRead;
        int mask = (0xFF >> (8 - toRead)) << bitsToNotRead;
        result = (bytes[byteOffset] & mask) >> bitsToNotRead;
        numBits -= toRead;
        bitOffset += toRead;
        if (bitOffset == 8) {
          bitOffset = 0;
          byteOffset++;
        }
      }
  
      // Next read whole bytes
      if (numBits > 0) {
        while (numBits >= 8) {
          result = (result << 8) | (bytes[byteOffset] & 0xFF);
          byteOffset++;
          numBits -= 8;
        }
  
        // Finally read a partial byte
        if (numBits > 0) {
          int bitsToNotRead = 8 - numBits;
          int mask = (0xFF >> bitsToNotRead) << bitsToNotRead;
          result = (result << numBits) | ((bytes[byteOffset] & mask) >> bitsToNotRead);
          bitOffset += numBits;
        }
      }
  
      return result;
    }
  
    /**
     * @return number of bits that can be read successfully
     */
    public int available() {
      return 8 * (bytes.length - byteOffset) - bitOffset;
    }
  
  }
  