var spd sparseDatas
		var spb []byte
		if len(hdr.SparseHoles) > 0 {
			sph := append([]sparseEntry{}, hdr.SparseHoles...) // Copy sparse map
			sph = alignSparseEntries(sph, hdr.Size)
			spd = invertSparseEntries(sph, hdr.Size)

			// Format the sparse map.
			hdr.Size = 0 // Replace with encoded size
			spb = append(strconv.AppendInt(spb, int64(len(spd)), 10), '\n')
			for _, s := range spd {
				hdr.Size += s.Length

			fw = &regFileWriter{w, maker.size}
			wantStr = maker.wantStr
		case makeSparse:
			if !validateSparseEntries(maker.sph, maker.size) {
				t.Fatalf("invalid sparse map: %v", maker.sph)
			}
			spd := invertSparseEntries(maker.sph, maker.size)
			fw = &regFileWriter{w, maker.makeReg.size}
			fw = &sparseFileWriter{fw, spd, 0}
			wantStr = maker.makeReg.wantStr
		default:

			fr = &regFileReader{r, maker.size}
		case makeSparse:
			if !validateSparseEntries(maker.spd, maker.size) {
				t.Fatalf("invalid sparse map: %v", maker.spd)
			}
			sph := invertSparseEntries(maker.spd, maker.size)
			r := testNonEmptyReader{strings.NewReader(maker.makeReg.str)}
			fr = &regFileReader{r, maker.makeReg.size}
			fr = &sparseFileReader{fr, sph, 0}
		default: