1 // Copyright (c) 2019 The Chromium Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
4
5 #include "quiche/quic/core/qpack/qpack_required_insert_count.h"
6
7 #include <limits>
8
9 #include "quiche/quic/platform/api/quic_logging.h"
10
11 namespace quic {
12
QpackEncodeRequiredInsertCount(uint64_t required_insert_count,uint64_t max_entries)13 uint64_t QpackEncodeRequiredInsertCount(uint64_t required_insert_count,
14 uint64_t max_entries) {
15 if (required_insert_count == 0) {
16 return 0;
17 }
18
19 return required_insert_count % (2 * max_entries) + 1;
20 }
21
QpackDecodeRequiredInsertCount(uint64_t encoded_required_insert_count,uint64_t max_entries,uint64_t total_number_of_inserts,uint64_t * required_insert_count)22 bool QpackDecodeRequiredInsertCount(uint64_t encoded_required_insert_count,
23 uint64_t max_entries,
24 uint64_t total_number_of_inserts,
25 uint64_t* required_insert_count) {
26 if (encoded_required_insert_count == 0) {
27 *required_insert_count = 0;
28 return true;
29 }
30
31 // |max_entries| is calculated by dividing an unsigned 64-bit integer by 32,
32 // precluding all calculations in this method from overflowing.
33 QUICHE_DCHECK_LE(max_entries, std::numeric_limits<uint64_t>::max() / 32);
34
35 if (encoded_required_insert_count > 2 * max_entries) {
36 return false;
37 }
38
39 *required_insert_count = encoded_required_insert_count - 1;
40 QUICHE_DCHECK_LT(*required_insert_count,
41 std::numeric_limits<uint64_t>::max() / 16);
42
43 uint64_t current_wrapped = total_number_of_inserts % (2 * max_entries);
44 QUICHE_DCHECK_LT(current_wrapped, std::numeric_limits<uint64_t>::max() / 16);
45
46 if (current_wrapped >= *required_insert_count + max_entries) {
47 // Required Insert Count wrapped around 1 extra time.
48 *required_insert_count += 2 * max_entries;
49 } else if (current_wrapped + max_entries < *required_insert_count) {
50 // Decoder wrapped around 1 extra time.
51 current_wrapped += 2 * max_entries;
52 }
53
54 if (*required_insert_count >
55 std::numeric_limits<uint64_t>::max() - total_number_of_inserts) {
56 return false;
57 }
58
59 *required_insert_count += total_number_of_inserts;
60
61 // Prevent underflow, also disallow invalid value 0 for Required Insert Count.
62 if (current_wrapped >= *required_insert_count) {
63 return false;
64 }
65
66 *required_insert_count -= current_wrapped;
67
68 return true;
69 }
70
71 } // namespace quic
72