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From "fredwang_00 (JIRA)" <j...@apache.org>
Subject [jira] [Created] (COMPRESS-363) Overflow in BitInputStream
Date Wed, 29 Jun 2016 09:19:45 GMT
fredwang_00 created COMPRESS-363:
------------------------------------

             Summary: 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


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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