code: func pack9(in []uint32) uint32 {
  	return 2<<28 |
  		in[0]<<1 |
  		in[1]<<4 |
  		in[2]<<7 |
  		in[3]<<10 |
  		in[4]<<13 |
  		in[5]<<16 |
  		in[6]<<19 |
  		in[7]<<22 |
  		in[8]<<25
  }
docs: // pack9 packs 9 values from in using 3 bits each