| /* |
| * 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; |
| |
| /** |
| * 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 |
| */ |
| public BitwiseInputStream(byte buf[]) { |
| mBuf = buf; |
| mEnd = buf.length << 3; |
| mPos = 0; |
| } |
| |
| /** |
| * Return the number of bit still available for reading. |
| */ |
| 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) |
| */ |
| 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 |
| */ |
| 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 |
| */ |
| public void skip(int bits) throws AccessException { |
| if ((mPos + bits) > mEnd) { |
| throw new AccessException("illegal skip " + |
| "(pos " + mPos + ", end " + mEnd + ", bits " + bits + ")"); |
| } |
| mPos += bits; |
| } |
| } |