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From "Stefan Bodewig (JIRA)" <j...@apache.org>
Subject [jira] [Resolved] (COMPRESS-363) Overflow in BitInputStream
Date Fri, 01 Jul 2016 19:40:10 GMT

     [ https://issues.apache.org/jira/browse/COMPRESS-363?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Stefan Bodewig resolved COMPRESS-363.
-------------------------------------
       Resolution: Fixed
    Fix Version/s: 1.13

Many thanks, I've created a unit test from your example.

Should be fixed with git commit 52dd590.

> Overflow in BitInputStream
> --------------------------
>
>                 Key: COMPRESS-363
>                 URL: https://issues.apache.org/jira/browse/COMPRESS-363
>             Project: Commons Compress
>          Issue Type: Bug
>          Components: Compressors
>    Affects Versions: 1.12
>            Reporter: fredwang_00
>             Fix For: 1.13
>
>
> in Class BitInputStream.java(\src\main\java\org\apache\commons\compress\utils),
> funcion:
>  public long readBits(final int count) throws IOException {
>         if (count < 0 || count > MAXIMUM_CACHE_SIZE) {
>             throw new IllegalArgumentException("count must not be negative or greater
than " + MAXIMUM_CACHE_SIZE);
>         }
>         while (bitsCachedSize < count) {
>             final long nextByte = in.read();
>             if (nextByte < 0) {
>                 return nextByte;
>             }
>             if (byteOrder == ByteOrder.LITTLE_ENDIAN) {
>                 bitsCached |= (nextByte << bitsCachedSize);
>             } else {
>                 bitsCached <<= 8;
>                 bitsCached |= nextByte;
>             }
>             bitsCachedSize += 8;
>         }
>         final long bitsOut;
>         if (byteOrder == ByteOrder.LITTLE_ENDIAN) {
>             bitsOut = (bitsCached & MASKS[count]);
>             bitsCached >>>= count;
>         } else {
>             bitsOut = (bitsCached >> (bitsCachedSize - count)) & MASKS[count];
>         }
>         bitsCachedSize -= count;
>         return bitsOut;
>     }
> I think here "bitsCached |= (nextByte << bitsCachedSize);" will overflow in some
cases. for example, below is a test case:
> public static void test() {
>         ByteArrayInputStream in = new ByteArrayInputStream(new byte[]{87, 45, 66, 15,
>                                                                       90, 29, 88, 61,
33, 74});
>         BitInputStream bin = new BitInputStream(in, ByteOrder.LITTLE_ENDIAN);
>         try {
>             long ret = bin.readBits(5);
>             ret = bin.readBits(63);
>             ret = bin.readBits(12);
>         } catch (Exception e) {
>             e.printStackTrace();
>         }
> }
> overflow occur in "bin.readBits(63);" , so ,result in wrong result from  "bin.readBits(12);"




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