BitwiseInputStream.java revision e564b19ed2f6b8b5667648254bc6c6859bb536e7
183917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink/* 283917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink * Copyright (C) 2008 The Android Open Source Project 383917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink * 483917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink * Licensed under the Apache License, Version 2.0 (the "License"); 583917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink * you may not use this file except in compliance with the License. 683917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink * You may obtain a copy of the License at 783917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink * 883917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink * http://www.apache.org/licenses/LICENSE-2.0 983917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink * 1083917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink * Unless required by applicable law or agreed to in writing, software 1183917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink * distributed under the License is distributed on an "AS IS" BASIS, 1283917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 1383917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink * See the License for the specific language governing permissions and 1483917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink * limitations under the License. 1583917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink */ 1683917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink 1783917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalinkpackage com.android.internal.util; 1883917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink 1983917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink/** 2083917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink * An object that provides bitwise incremental read access to a byte array. 2183917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink * 2283917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink * This is useful, for example, when accessing a series of fields that 2383917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink * may not be aligned on byte boundaries. 2483917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink * 2583917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink * NOTE -- This class is not threadsafe. 2683917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink */ 2783917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalinkpublic class BitwiseInputStream { 2883917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink 2983917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink // The byte array being read from. 3083917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink private byte[] mBuf; 3183917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink 3283917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink // The current position offset, in bits, from the msb in byte 0. 3383917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink private int mPos; 3483917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink 3583917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink // The last valid bit offset. 3683917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink private int mEnd; 3783917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink 3883917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink /** 3983917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink * An exception to report access problems. 4083917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink */ 4183917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink public static class AccessException extends Exception { 4283917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink public AccessException(String s) { 4383917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink super("BitwiseInputStream access failed: " + s); 4483917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink } 4583917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink } 4683917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink 4783917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink /** 4883917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink * Create object from byte array. 4983917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink * 5083917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink * @param buf a byte array containing data 5183917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink */ 5283917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink public BitwiseInputStream(byte buf[]) { 5383917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink mBuf = buf; 54e564b19ed2f6b8b5667648254bc6c6859bb536e7Tammo Spalink mEnd = buf.length << 3; 5583917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink mPos = 0; 5683917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink } 5783917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink 5883917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink /** 5983917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink * Return the number of bit still available for reading. 6083917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink */ 6183917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink public int available() { 6283917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink return mEnd - mPos; 6383917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink } 6483917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink 6583917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink /** 6683917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink * Read some data and increment the current position. 6783917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink * 6883917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink * @param bits the amount of data to read (gte 0, lte 8) 6983917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink * 7083917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink * @return byte of read data (possibly partially filled, from lsb) 7183917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink */ 7283917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink public byte read(int bits) throws AccessException { 73e564b19ed2f6b8b5667648254bc6c6859bb536e7Tammo Spalink int index = mPos >>> 3; 74e564b19ed2f6b8b5667648254bc6c6859bb536e7Tammo Spalink int offset = 16 - (mPos & 0x07) - bits; // &7==%8 7583917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink if ((bits < 0) || (bits > 8) || ((mPos + bits) > mEnd)) { 7683917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink throw new AccessException("illegal read " + 7783917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink "(pos " + mPos + ", end " + mEnd + ", bits " + bits + ")"); 7883917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink } 79e564b19ed2f6b8b5667648254bc6c6859bb536e7Tammo Spalink int data = (mBuf[index] & 0x00FF) << 8; 8083917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink if (offset < 8) data |= (mBuf[index + 1] & 0xFF); 8183917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink data >>>= offset; 8283917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink data &= (-1 >>> (32 - bits)); 8383917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink mPos += bits; 8483917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink return (byte)data; 8583917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink } 8683917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink 8783917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink /** 8883917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink * Read data in bulk into a byte array and increment the current position. 8983917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink * 9083917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink * @param bits the amount of data to read 9183917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink * 9283917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink * @return newly allocated byte array of read data 9383917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink */ 9483917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink public byte[] readByteArray(int bits) throws AccessException { 95e564b19ed2f6b8b5667648254bc6c6859bb536e7Tammo Spalink int bytes = (bits >>> 3) + ((bits & 0x07) > 0 ? 1 : 0); // &7==%8 9683917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink byte[] arr = new byte[bytes]; 9783917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink for (int i = 0; i < bytes; i++) { 98e564b19ed2f6b8b5667648254bc6c6859bb536e7Tammo Spalink int increment = Math.min(8, bits - (i << 3)); 9983917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink arr[i] = (byte)(read(increment) << (8 - increment)); 10083917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink } 10183917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink return arr; 10283917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink } 10383917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink 10483917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink /** 10583917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink * Increment the current position and ignore contained data. 10683917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink * 10783917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink * @param bits the amount by which to increment the position 10883917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink */ 10983917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink public void skip(int bits) throws AccessException { 11083917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink if ((mPos + bits) > mEnd) { 11183917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink throw new AccessException("illegal skip " + 11283917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink "(pos " + mPos + ", end " + mEnd + ", bits " + bits + ")"); 11383917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink } 11483917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink mPos += bits; 11583917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink } 11683917db040bd7498ebca3b74f879dc1c9e223d8eTammo Spalink} 117