Added get bits function for arrays

src/zutil/ByteUtil.java

@@ -57,7 +57,18 @@ public class ByteUtil {
     }
 
     /**
-     * Creates a new sub byte from index and with a length
+     * Creates a new sub byte from index and with the given length length
+     *
+     * @param   data    is the byte data
+     * @param   length  is the length of bits to return, valid values 1-8
+     * @return a new byte containing a sub byte defined by the index and length
+     */
+    public static byte getBits(byte data, int length){
+        return getBits(data, 0, length);
+    }
+
+    /**
+     * Creates a new sub byte from index and with the given length length
      *
      * @param   data    is the byte data
      * @param   index   is the bit index, valid values 0-7
@@ -69,6 +80,21 @@ public class ByteUtil {
         return  ret;
     }
 
+    /**
+     * Creates a new sub byte array with only the given length of bits from the data array.
+     *
+     * @param   data    is the byte data array
+     * @param   length  is the length of bits to return
+     * @return a new byte array of te given length containing the given data.
+     */
+    public static byte[] getBits(byte[] data, int length){
+        byte[] dest = new byte[(int) Math.ceil(length/8.0)];
+        System.arraycopy(data, 0, dest, 0, Math.min(data.length, dest.length));
+        if(length % 8 != 0)
+            dest[dest.length-1] = getBits(dest[dest.length-1], length % 8);
+        return dest;
+    }
+
     /**
      * Returns a byte bitmask
      *

test/zutil/ByteUtilTest.java

@@ -26,6 +26,7 @@ package zutil;
 
 import org.junit.Test;
 
+import static org.junit.Assert.assertArrayEquals;
 import static org.junit.Assert.assertEquals;
 
 
@@ -45,4 +46,16 @@ public class ByteUtilTest {
 
         assertEquals((byte)0xFF, ByteUtil.getShiftedBits((byte)0b1111_1111, 7, 8));
     }
+
+
+    @Test
+    public void getBitsArray(){
+        assertArrayEquals(new byte[]{}, ByteUtil.getBits(new byte[]{0x00}, 0));
+        assertArrayEquals(new byte[]{0x00}, ByteUtil.getBits(new byte[]{}, 1));
+        assertArrayEquals(new byte[]{0x00,0x00,0x00,0x00}, ByteUtil.getBits(new byte[]{0x00}, 32));
+        assertArrayEquals(new byte[]{0x00}, ByteUtil.getBits(new byte[]{0x00,0x10}, 1));
+        assertArrayEquals(new byte[]{0x00}, ByteUtil.getBits(new byte[]{0x00,0x10}, 8));
+        assertArrayEquals(new byte[]{0x00,0x01}, ByteUtil.getBits(new byte[]{0x00,0x01}, 9));
+        assertArrayEquals(new byte[]{0x00,0x01}, ByteUtil.getBits(new byte[]{0x00,0x11}, 9));
+    }
 }