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 #pragma once
15
16 #include <algorithm>
17 #include <cstddef>
18 #include <cstring>
19 #include <initializer_list>
20 #include <span>
21 #include <utility>
22
23 #include "pw_bytes/span.h"
24 #include "pw_kvs/io.h"
25 #include "pw_status/status_with_size.h"
26
27 namespace pw {
28
29 // Returns the value rounded down to the nearest multiple of alignment.
AlignDown(size_t value,size_t alignment)30 constexpr size_t AlignDown(size_t value, size_t alignment) {
31 return (value / alignment) * alignment;
32 }
33
34 // Returns the value rounded up to the nearest multiple of alignment.
AlignUp(size_t value,size_t alignment)35 constexpr size_t AlignUp(size_t value, size_t alignment) {
36 return (value + alignment - 1) / alignment * alignment;
37 }
38
39 // Returns the number of padding bytes required to align the provided length.
Padding(size_t length,size_t alignment)40 constexpr size_t Padding(size_t length, size_t alignment) {
41 return AlignUp(length, alignment) - length;
42 }
43
44 // Class for managing aligned writes. Stores data in an intermediate buffer and
45 // calls an output function with aligned data as the buffer becomes full. Any
46 // bytes remaining in the buffer are written to the output when Flush() is
47 // called or the AlignedWriter goes out of scope.
48 class AlignedWriter {
49 public:
AlignedWriter(std::span<std::byte> buffer,size_t alignment_bytes,Output & writer)50 AlignedWriter(std::span<std::byte> buffer,
51 size_t alignment_bytes,
52 Output& writer)
53 : buffer_(buffer.data()),
54 write_size_(AlignDown(buffer.size(), alignment_bytes)),
55 alignment_bytes_(alignment_bytes),
56 output_(writer),
57 bytes_written_(0),
58 bytes_in_buffer_(0) {
59 // TODO(hepler): Add DCHECK to ensure that buffer.size() >= alignment_bytes.
60 }
61
~AlignedWriter()62 ~AlignedWriter() { Flush(); }
63
64 // Writes bytes to the AlignedWriter. The output may be called if the internal
65 // buffer is filled.
66 //
67 // The size in the return value is the total number of bytes for which a write
68 // has been attempted since Flush or Reset. The size is set for both
69 // successful and failed Write calls. On a failed write call, knowing the
70 // bytes attempted may be important when working with flash memory, since it
71 // can only be written once between erases.
72 StatusWithSize Write(std::span<const std::byte> data);
73
Write(const void * data,size_t size)74 StatusWithSize Write(const void* data, size_t size) {
75 return Write(
76 std::span<const std::byte>(static_cast<const std::byte*>(data), size));
77 }
78
79 // Reads size bytes from the input and writes them to the output.
80 StatusWithSize Write(Input& input, size_t size);
81
82 // Flush and reset the AlignedWriter. Any remaining bytes in the buffer are
83 // zero-padded to an alignment boundary and written to the output. Flush is
84 // automatically called when the AlignedWriter goes out of scope.
85 StatusWithSize Flush();
86
87 private:
88 static constexpr std::byte kPadByte = static_cast<std::byte>(0);
89
90 StatusWithSize AddBytesToBuffer(size_t bytes_added);
91
92 std::byte* const buffer_;
93 const size_t write_size_;
94 const size_t alignment_bytes_;
95
96 Output& output_;
97 size_t bytes_written_;
98 size_t bytes_in_buffer_;
99 };
100
101 // Declares an AlignedWriter with a built-in buffer.
102 template <size_t kBufferSize>
103 class AlignedWriterBuffer : public AlignedWriter {
104 public:
105 template <typename... Args>
AlignedWriterBuffer(Args &&...aligned_writer_args)106 AlignedWriterBuffer(Args&&... aligned_writer_args)
107 : AlignedWriter(buffer_, std::forward<Args>(aligned_writer_args)...) {}
108
109 private:
110 std::byte buffer_[kBufferSize];
111 };
112
113 // Writes data from multiple buffers using an AlignedWriter.
114 template <size_t kBufferSize>
AlignedWrite(Output & output,size_t alignment_bytes,std::span<const std::span<const std::byte>> data)115 StatusWithSize AlignedWrite(Output& output,
116 size_t alignment_bytes,
117 std::span<const std::span<const std::byte>> data) {
118 // TODO: This should convert to PW_CHECK once that is available for use in
119 // host tests.
120 if (alignment_bytes > kBufferSize) {
121 return StatusWithSize::Internal();
122 }
123
124 AlignedWriterBuffer<kBufferSize> buffer(alignment_bytes, output);
125
126 for (const std::span<const std::byte>& chunk : data) {
127 StatusWithSize result = buffer.Write(chunk);
128 if (!result.ok()) {
129 return result;
130 }
131 }
132
133 return buffer.Flush();
134 }
135
136 // Calls AlignedWrite with an initializer list.
137 template <size_t kBufferSize>
AlignedWrite(Output & output,size_t alignment_bytes,std::initializer_list<std::span<const std::byte>> data)138 StatusWithSize AlignedWrite(
139 Output& output,
140 size_t alignment_bytes,
141 std::initializer_list<std::span<const std::byte>> data) {
142 return AlignedWrite<kBufferSize>(
143 output,
144 alignment_bytes,
145 std::span<const ConstByteSpan>(data.begin(), data.size()));
146 }
147
148 } // namespace pw
149