1 // Copyright 2020 The Pigweed Authors
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License"); you may not
4 // use this file except in compliance with the License. You may obtain a copy of
5 // the License at
6 //
7 // https://www.apache.org/licenses/LICENSE-2.0
8 //
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
11 // WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
12 // License for the specific language governing permissions and limitations under
13 // the License.
14
15 #include "pw_tokenizer/encode_args.h"
16
17 #include <algorithm>
18 #include <cstring>
19
20 #include "pw_preprocessor/compiler.h"
21 #include "pw_varint/varint.h"
22
23 namespace pw {
24 namespace tokenizer {
25 namespace {
26
27 // Declare the types as an enum for convenience.
28 enum class ArgType : uint8_t {
29 kInt = PW_TOKENIZER_ARG_TYPE_INT,
30 kInt64 = PW_TOKENIZER_ARG_TYPE_INT64,
31 kDouble = PW_TOKENIZER_ARG_TYPE_DOUBLE,
32 kString = PW_TOKENIZER_ARG_TYPE_STRING,
33 };
34
EncodeInt(int value,const std::span<std::byte> & output)35 size_t EncodeInt(int value, const std::span<std::byte>& output) {
36 return varint::Encode(value, std::as_writable_bytes(output));
37 }
38
EncodeInt64(int64_t value,const std::span<std::byte> & output)39 size_t EncodeInt64(int64_t value, const std::span<std::byte>& output) {
40 return varint::Encode(value, std::as_writable_bytes(output));
41 }
42
EncodeFloat(float value,const std::span<std::byte> & output)43 size_t EncodeFloat(float value, const std::span<std::byte>& output) {
44 if (output.size() < sizeof(value)) {
45 return 0;
46 }
47 std::memcpy(output.data(), &value, sizeof(value));
48 return sizeof(value);
49 }
50
EncodeString(const char * string,const std::span<std::byte> & output)51 size_t EncodeString(const char* string, const std::span<std::byte>& output) {
52 // The top bit of the status byte indicates if the string was truncated.
53 static constexpr size_t kMaxStringLength = 0x7Fu;
54
55 if (output.empty()) { // At least one byte is needed for the status/size.
56 return 0;
57 }
58
59 if (string == nullptr) {
60 string = "NULL";
61 }
62
63 // Subtract 1 to save room for the status byte.
64 const size_t max_bytes =
65 std::min(static_cast<size_t>(output.size()), kMaxStringLength) - 1;
66
67 // Scan the string to find out how many bytes to copy.
68 size_t bytes_to_copy = 0;
69 std::byte overflow_bit = std::byte(0);
70
71 while (string[bytes_to_copy] != '\0') {
72 if (bytes_to_copy == max_bytes) {
73 overflow_bit = std::byte('\x80');
74 break;
75 }
76 bytes_to_copy += 1;
77 }
78
79 output[0] = static_cast<std::byte>(bytes_to_copy) | overflow_bit;
80 std::memcpy(output.data() + 1, string, bytes_to_copy);
81
82 return bytes_to_copy + 1; // include the status byte in the total
83 }
84
85 } // namespace
86
EncodeArgs(pw_tokenizer_ArgTypes types,va_list args,std::span<std::byte> output)87 size_t EncodeArgs(pw_tokenizer_ArgTypes types,
88 va_list args,
89 std::span<std::byte> output) {
90 size_t arg_count = types & PW_TOKENIZER_TYPE_COUNT_MASK;
91 types >>= PW_TOKENIZER_TYPE_COUNT_SIZE_BITS;
92
93 size_t encoded_bytes = 0;
94 while (arg_count != 0u) {
95 // How many bytes were encoded; 0 indicates that there wasn't enough space.
96 size_t argument_bytes = 0;
97
98 switch (static_cast<ArgType>(types & 0b11u)) {
99 case ArgType::kInt:
100 argument_bytes = EncodeInt(va_arg(args, int), output);
101 break;
102 case ArgType::kInt64:
103 argument_bytes = EncodeInt64(va_arg(args, int64_t), output);
104 break;
105 case ArgType::kDouble:
106 argument_bytes =
107 EncodeFloat(static_cast<float>(va_arg(args, double)), output);
108 break;
109 case ArgType::kString:
110 argument_bytes = EncodeString(va_arg(args, const char*), output);
111 break;
112 }
113
114 // If zero bytes were encoded, the encoding buffer is full.
115 if (argument_bytes == 0u) {
116 break;
117 }
118
119 output = output.subspan(argument_bytes);
120 encoded_bytes += argument_bytes;
121
122 arg_count -= 1;
123 types >>= 2; // each argument type is encoded in two bits
124 }
125
126 return encoded_bytes;
127 }
128
129 } // namespace tokenizer
130 } // namespace pw
131