Playing with bits using Java

How can I optimize the following class?

prepareSharing packs bits on left and prepareMask counts the required bits for encoding integers between zero and max.

public class KeyFactory
{      
  public static short[] prepareSharing( short[] sharing, int mask )
  {
    // Ensure mask is unsigned short
    //
    mask &= 0xFFFF;

    // Search first zero bits
    //
    // BE CAREFUL : raise java.lang.ArrayIndexOutOfBoundsException if there aren't enough bits available
    //
    int i = 0;
    while( ( sharing[i] & 0xFFFF ) == 0xFFFF )
      i++;

    // Handle masks larger than available free bits
    //
    int remaining = ~( sharing[i] & 0xFFFF ) & 0x0000FFFF;

    if( remaining < mask )
    {
      for( ;remaining > 0; remaining >>= 1, mask >>= 1 );      
      sharing[i++] |= 0xFFFF;
    }

    // Pack bits
    //
    int temporary, current = sharing[i];
    for( temporary = ( current | mask ) & 0xFFFF; ( ( current | ( mask << 1 ) ) & 0xFFFF ) > temporary; mask <<= 1, temporary = ( current | mask ) & 0xFFFF );

    sharing[i] = 0;
    sharing[i] |= temporary;

    return sharing;
  }

  public static int prepareMask( int maxCount )
  {
    int mask = 0;

    for( int i = 0; i < 16; i++ )
      if( maxCount >> i > 0 )
        mask |= 1 << i;

    return mask;
  }
}

Tests:

import org.junit.Assert;
import org.junit.Test;

import fr.meuns.render.KeyFactory;

public class TestKeyFactory
{
  @Test
  public void testPrepareMask()
  {
    Assert.assertEquals( 0b0001 ,KeyFactory.prepareMask( 1 ) );
    Assert.assertEquals( 0b0011 ,KeyFactory.prepareMask( 2 ) );
    Assert.assertEquals( 0b0011 ,KeyFactory.prepareMask( 3 ) );
    Assert.assertEquals( 0b0111 ,KeyFactory.prepareMask( 4 ) );
    Assert.assertEquals( 0b0111 ,KeyFactory.prepareMask( 5 ) );
    Assert.assertEquals( 0b0111 ,KeyFactory.prepareMask( 6 ) );
    Assert.assertEquals( 0b0111 ,KeyFactory.prepareMask( 7 ) );

    for( int i = 8; i < 16; i++ )
      Assert.assertEquals( 0b001111 ,KeyFactory.prepareMask( i ) );

    for( int i = 16; i < 32; i++ )
      Assert.assertEquals( 0b011111 ,KeyFactory.prepareMask( i ) );

    for( int i = 32; i < 64; i++ )
      Assert.assertEquals( 0b111111 ,KeyFactory.prepareMask( i ) );
  }

  @Test
  public void testPackSharing_0x0007()
  {
    short[] sharing = new short[] {
      0x0000, 0x0000
    };

    sharing = KeyFactory.prepareSharing( sharing, (short)0x0007 );    
    Assert.assertEquals( 0xE000, sharing[0] & 0xFFFF );
    Assert.assertEquals( 0x0000, sharing[1] & 0xFFFF );

    sharing = KeyFactory.prepareSharing( sharing, (short)0x0007 );    
    Assert.assertEquals( 0xFC00, sharing[0] & 0xFFFF );
    Assert.assertEquals( 0x0000, sharing[1] & 0xFFFF );

    sharing = KeyFactory.prepareSharing( sharing, (short)0x0007 );    
    Assert.assertEquals( 0xFF80, sharing[0] & 0xFFFF );
    Assert.assertEquals( 0x0000, sharing[1] & 0xFFFF );

    sharing = KeyFactory.prepareSharing( sharing, (short)0x0007 );    
    Assert.assertEquals( 0xFFF0, sharing[0] & 0xFFFF );
    Assert.assertEquals( 0x0000, sharing[1] & 0xFFFF );

    sharing = KeyFactory.prepareSharing( sharing, (short)0x0007 );    
    Assert.assertEquals( 0xFFFE, sharing[0] & 0xFFFF );
    Assert.assertEquals( 0x0000, sharing[1] & 0xFFFF );

    sharing = KeyFactory.prepareSharing( sharing, (short)0x0007 );    
    Assert.assertEquals( 0xFFFF, sharing[0] & 0xFFFF );
    Assert.assertEquals( 0xC000, sharing[1] & 0xFFFF );

    sharing = KeyFactory.prepareSharing( sharing, (short)0x0007 );    
    Assert.assertEquals( 0xFFFF, sharing[0] & 0xFFFF );
    Assert.assertEquals( 0xF800, sharing[1] & 0xFFFF );

    sharing = KeyFactory.prepareSharing( sharing, (short)0x0007 );    
    Assert.assertEquals( 0xFFFF, sharing[0] & 0xFFFF );
    Assert.assertEquals( 0xFF00, sharing[1] & 0xFFFF );

    sharing = KeyFactory.prepareSharing( sharing, (short)0x0007 );    
    Assert.assertEquals( 0xFFFF, sharing[0] & 0xFFFF );
    Assert.assertEquals( 0xFFE0, sharing[1] & 0xFFFF );

    sharing = KeyFactory.prepareSharing( sharing, (short)0x0007 );    
    Assert.assertEquals( 0xFFFF, sharing[0] & 0xFFFF );
    Assert.assertEquals( 0xFFFC, sharing[1] & 0xFFFF );
  }

  @Test
  public void testPackSharing_0x003F()
  {
    short[] sharing = new short[] {
      0x0000, 0x0000
    };

    sharing = KeyFactory.prepareSharing( sharing, (short)0x003F );    
    Assert.assertEquals( 0xFC00, sharing[0] & 0xFFFF );
    Assert.assertEquals( 0x0000, sharing[1] & 0xFFFF );

    sharing = KeyFactory.prepareSharing( sharing, (short)0x003F );    
    Assert.assertEquals( 0xFFF0, sharing[0] & 0xFFFF );
    Assert.assertEquals( 0x0000, sharing[1] & 0xFFFF );

    sharing = KeyFactory.prepareSharing( sharing, (short)0x003F );    
    Assert.assertEquals( 0xFFFF, sharing[0] & 0xFFFF );
    Assert.assertEquals( 0xC000, sharing[1] & 0xFFFF );

    sharing = KeyFactory.prepareSharing( sharing, (short)0x003F );    
    Assert.assertEquals( 0xFFFF, sharing[0] & 0xFFFF );
    Assert.assertEquals( 0xFF00, sharing[1] & 0xFFFF );

    sharing = KeyFactory.prepareSharing( sharing, (short)0x003F );    
    Assert.assertEquals( 0xFFFF, sharing[0] & 0xFFFF );
    Assert.assertEquals( 0xFFFC, sharing[1] & 0xFFFF );
  }
}