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      1 /*
      2  * Copyright (C) 2008 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 package com.android.dx.util;
     18 
     19 /**
     20  * Reads and writes DWARFv3 LEB 128 signed and unsigned integers. See DWARF v3
     21  * section 7.6.
     22  */
     23 public final class Leb128Utils {
     24     /**
     25      * This class is uninstantiable.
     26      */
     27     private Leb128Utils() {
     28         // This space intentionally left blank.
     29     }
     30 
     31     /**
     32      * Gets the number of bytes in the unsigned LEB128 encoding of the
     33      * given value.
     34      *
     35      * @param value the value in question
     36      * @return its write size, in bytes
     37      */
     38     public static int unsignedLeb128Size(int value) {
     39         // TODO: This could be much cleverer.
     40 
     41         int remaining = value >> 7;
     42         int count = 0;
     43 
     44         while (remaining != 0) {
     45             remaining >>= 7;
     46             count++;
     47         }
     48 
     49         return count + 1;
     50     }
     51 
     52     /**
     53      * Gets the number of bytes in the signed LEB128 encoding of the
     54      * given value.
     55      *
     56      * @param value the value in question
     57      * @return its write size, in bytes
     58      */
     59     public static int signedLeb128Size(int value) {
     60         // TODO: This could be much cleverer.
     61 
     62         int remaining = value >> 7;
     63         int count = 0;
     64         boolean hasMore = true;
     65         int end = ((value & Integer.MIN_VALUE) == 0) ? 0 : -1;
     66 
     67         while (hasMore) {
     68             hasMore = (remaining != end)
     69                 || ((remaining & 1) != ((value >> 6) & 1));
     70 
     71             value = remaining;
     72             remaining >>= 7;
     73             count++;
     74         }
     75 
     76         return count;
     77     }
     78 
     79     /**
     80      * Reads an signed integer from {@code in}.
     81      */
     82     public static int readSignedLeb128(ByteInput in) {
     83         int result = 0;
     84         int cur;
     85         int count = 0;
     86         int signBits = -1;
     87 
     88         do {
     89             cur = in.readByte() & 0xff;
     90             result |= (cur & 0x7f) << (count * 7);
     91             signBits <<= 7;
     92             count++;
     93         } while (((cur & 0x80) == 0x80) && count < 5);
     94 
     95         if ((cur & 0x80) == 0x80) {
     96             throw new DexException("invalid LEB128 sequence");
     97         }
     98 
     99         // Sign extend if appropriate
    100         if (((signBits >> 1) & result) != 0 ) {
    101             result |= signBits;
    102         }
    103 
    104         return result;
    105     }
    106 
    107     /**
    108      * Reads an unsigned integer from {@code in}.
    109      */
    110     public static int readUnsignedLeb128(ByteInput in) {
    111         int result = 0;
    112         int cur;
    113         int count = 0;
    114 
    115         do {
    116             cur = in.readByte() & 0xff;
    117             result |= (cur & 0x7f) << (count * 7);
    118             count++;
    119         } while (((cur & 0x80) == 0x80) && count < 5);
    120 
    121         if ((cur & 0x80) == 0x80) {
    122             throw new DexException("invalid LEB128 sequence");
    123         }
    124 
    125         return result;
    126     }
    127 
    128     /**
    129      * Writes {@code value} as an unsigned integer to {@code out}, starting at
    130      * {@code offset}. Returns the number of bytes written.
    131      */
    132     public static void writeUnsignedLeb128(ByteOutput out, int value) {
    133         int remaining = value >>> 7;
    134 
    135         while (remaining != 0) {
    136             out.writeByte((byte) ((value & 0x7f) | 0x80));
    137             value = remaining;
    138             remaining >>>= 7;
    139         }
    140 
    141         out.writeByte((byte) (value & 0x7f));
    142     }
    143 
    144     /**
    145      * Writes {@code value} as a signed integer to {@code out}, starting at
    146      * {@code offset}. Returns the number of bytes written.
    147      */
    148     public static void writeSignedLeb128(ByteOutput out, int value) {
    149         int remaining = value >> 7;
    150         boolean hasMore = true;
    151         int end = ((value & Integer.MIN_VALUE) == 0) ? 0 : -1;
    152 
    153         while (hasMore) {
    154             hasMore = (remaining != end)
    155                     || ((remaining & 1) != ((value >> 6) & 1));
    156 
    157             out.writeByte((byte) ((value & 0x7f) | (hasMore ? 0x80 : 0)));
    158             value = remaining;
    159             remaining >>= 7;
    160         }
    161     }
    162 }
    163