tmp := make([]byte, 72)
	for _, growLen := range []int{0, 100, 1000, 10000, 100000} {
		for _, startLen := range []int{0, 100, 1000, 10000, 100000} {
			xBytes := Repeat(x, startLen)

			buf := NewBuffer(xBytes)
			// If we read, this affects buf.off, which is good to test.
			readBytes, _ := buf.Read(tmp)
			yBytes := Repeat(y, growLen)
			allocs := testing.AllocsPerRun(100, func() {
				buf.Grow(growLen)
				buf.Write(yBytes)

1024                int16       1024 is in the set of 16-bit integers
42.0                byte        42 is in the set of unsigned 8-bit integers
1e10                uint64      10000000000 is in the set of unsigned 64-bit integers
2.718281828459045   float32     2.718281828459045 rounds to 2.7182817 which is in the set of float32 values

	ADDEX R3, R5, $3, R6            // 7cc32f54
	ADDEX R3, $3, R5, R6            // 7cc32f54
	ADDIS $8, R3                    // 3c630008
	ADD   $524288, R3               // 3c630008
	ADDIS $1000, R3, R4             // 3c8303e8

	ANDCC $1, R3                    // 70630001
	ANDCC $1, R3, R4                // 70640001
	ANDCC $-1, R4                   // 3be0ffff7fe42039

1024                int16       1024 is in the set of 16-bit integers
42.0                byte        42 is in the set of unsigned 8-bit integers
1e10                uint64      10000000000 is in the set of unsigned 64-bit integers
2.718281828459045   float32     2.718281828459045 rounds to 2.7182817 which is in the set of float32 values

							{Offset: 0e10, Length: 1e10 - 100},
							{Offset: 1e10, Length: 1e10 - 100},
							{Offset: 2e10, Length: 1e10 - 100},
							{Offset: 3e10, Length: 1e10 - 100},
							{Offset: 4e10, Length: 1e10 - 100},
							{Offset: 5e10, Length: 1e10 - 100},
						},
					}, nil},
					testReadFrom{fileOps{
						int64(1e10 - blockSize),
						strings.Repeat("\x00", blockSize-100) + strings.Repeat("0123456789", 10),

		wantValid:    true,
		wantAligned:  []sparseEntry{{0, 5000}},
		wantInverted: []sparseEntry{{5000, 0}},
	}, {
		in: []sparseEntry{{1000, 4000}}, size: 5000,
		wantValid:    true,
		wantAligned:  []sparseEntry{{1024, 3976}},
		wantInverted: []sparseEntry{{0, 1000}, {5000, 0}},
	}, {
		in: []sparseEntry{{0, 3000}}, size: 5000,
		wantValid:    true,
		wantAligned:  []sparseEntry{{0, 2560}},