1 //
2 //
3 // Copyright 2015 gRPC authors.
4 //
5 // Licensed under the Apache License, Version 2.0 (the "License");
6 // you may not use this file except in compliance with the License.
7 // You may obtain a copy of the License at
8 //
9 // http://www.apache.org/licenses/LICENSE-2.0
10 //
11 // Unless required by applicable law or agreed to in writing, software
12 // distributed under the License is distributed on an "AS IS" BASIS,
13 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 // See the License for the specific language governing permissions and
15 // limitations under the License.
16 //
17 //
18
19 #ifndef GRPC_SRC_CORE_EXT_TRANSPORT_CHTTP2_TRANSPORT_VARINT_H
20 #define GRPC_SRC_CORE_EXT_TRANSPORT_CHTTP2_TRANSPORT_VARINT_H
21
22 #include <grpc/support/port_platform.h>
23
24 #include <stdint.h>
25 #include <stdlib.h>
26
27 #include <grpc/support/log.h>
28
29 // Helpers for hpack varint encoding
30
31 namespace grpc_core {
32
33 // maximum value that can be bitpacked with the opcode if the opcode has a
34 // prefix of length prefix_bits
MaxInVarintPrefix(uint8_t prefix_bits)35 constexpr uint32_t MaxInVarintPrefix(uint8_t prefix_bits) {
36 return (1 << (8 - prefix_bits)) - 1;
37 }
38
39 // length of a value that needs varint tail encoding (it's bigger than can be
40 // bitpacked into the opcode byte) - returned value includes the length of the
41 // opcode byte
42 size_t VarintLength(size_t tail_value);
43 void VarintWriteTail(size_t tail_value, uint8_t* target, size_t tail_length);
44
45 template <uint8_t kPrefixBits>
46 class VarintWriter {
47 public:
48 static constexpr uint32_t kMaxInPrefix = MaxInVarintPrefix(kPrefixBits);
49
VarintWriter(size_t value)50 explicit VarintWriter(size_t value)
51 : value_(value),
52 length_(value < kMaxInPrefix ? 1 : VarintLength(value - kMaxInPrefix)) {
53 GPR_ASSERT(value <= UINT32_MAX);
54 }
55
value()56 size_t value() const { return value_; }
length()57 size_t length() const { return length_; }
58
Write(uint8_t prefix,uint8_t * target)59 void Write(uint8_t prefix, uint8_t* target) const {
60 if (length_ == 1) {
61 target[0] = prefix | value_;
62 } else {
63 target[0] = prefix | kMaxInPrefix;
64 VarintWriteTail(value_ - kMaxInPrefix, target + 1, length_ - 1);
65 }
66 }
67
68 private:
69 const size_t value_;
70 // length required to bitpack value_
71 const size_t length_;
72 };
73
74 } // namespace grpc_core
75
76 #endif // GRPC_SRC_CORE_EXT_TRANSPORT_CHTTP2_TRANSPORT_VARINT_H
77