content: /*
   * Copyright (C) 2008 The Android Open Source Project
   *
   * 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.android.internal.util;
  
  import android.annotation.UnsupportedAppUsage;
  
  /**
   * An object that provides bitwise incremental read access to a byte array.
   *
   * This is useful, for example, when accessing a series of fields that
   * may not be aligned on byte boundaries.
   *
   * NOTE -- This class is not threadsafe.
   */
  public class BitwiseInputStream {
  
      // The byte array being read from.
      private byte[] mBuf;
  
      // The current position offset, in bits, from the msb in byte 0.
      private int mPos;
  
      // The last valid bit offset.
      private int mEnd;
  
      /**
       * An exception to report access problems.
       */
      public static class AccessException extends Exception {
          public AccessException(String s) {
              super("BitwiseInputStream access failed: " + s);
          }
      }
  
      /**
       * Create object from byte array.
       *
       * @param buf a byte array containing data
       */
      @UnsupportedAppUsage
      public BitwiseInputStream(byte buf[]) {
          mBuf = buf;
          mEnd = buf.length << 3;
          mPos = 0;
      }
  
      /**
       * Return the number of bit still available for reading.
       */
      @UnsupportedAppUsage
      public int available() {
          return mEnd - mPos;
      }
  
      /**
       * Read some data and increment the current position.
       *
       * The 8-bit limit on access to bitwise streams is intentional to
       * avoid endianness issues.
       *
       * @param bits the amount of data to read (gte 0, lte 8)
       * @return byte of read data (possibly partially filled, from lsb)
       */
      @UnsupportedAppUsage
      public int read(int bits) throws AccessException {
          int index = mPos >>> 3;
          int offset = 16 - (mPos & 0x07) - bits;  // &7==%8
          if ((bits < 0) || (bits > 8) || ((mPos + bits) > mEnd)) {
              throw new AccessException("illegal read " +
                  "(pos " + mPos + ", end " + mEnd + ", bits " + bits + ")");
          }
          int data = (mBuf[index] & 0xFF) << 8;
          if (offset < 8) data |= mBuf[index + 1] & 0xFF;
          data >>>= offset;
          data &= (-1 >>> (32 - bits));
          mPos += bits;
          return data;
      }
  
      /**
       * Read data in bulk into a byte array and increment the current position.
       *
       * @param bits the amount of data to read
       * @return newly allocated byte array of read data
       */
      @UnsupportedAppUsage
      public byte[] readByteArray(int bits) throws AccessException {
          int bytes = (bits >>> 3) + ((bits & 0x07) > 0 ? 1 : 0);  // &7==%8
          byte[] arr = new byte[bytes];
          for (int i = 0; i < bytes; i++) {
              int increment = Math.min(8, bits - (i << 3));
              arr[i] = (byte)(read(increment) << (8 - increment));
          }
          return arr;
      }
  
      /**
       * Increment the current position and ignore contained data.
       *
       * @param bits the amount by which to increment the position
       */
      @UnsupportedAppUsage
      public void skip(int bits) throws AccessException {
          if ((mPos + bits) > mEnd) {
              throw new AccessException("illegal skip " +
                  "(pos " + mPos + ", end " + mEnd + ", bits " + bits + ")");
          }
          mPos += bits;
      }
  }
  