code: func (ix *Index) slice(off uint32, n int) []byte {
  	o := int(off)
  	if uint32(o) != off || n >= 0 && o+n > len(ix.data.d) {
  		corrupt()
  	}
  	if n < 0 {
  		return ix.data.d[o:]
  	}
  	return ix.data.d[o : o+n]
  }
docs: // slice returns the slice of index data starting at the given byte offset.
  // If n >= 0, the slice must have length at least n and is truncated to length n.