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// Copyright 2020 The Pigweed Authors
// Licensed under the Apache License, Version 2.0 (the "License"); you may not
// use this file except in compliance with the License. You may obtain a copy of
// the License at
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
// License for the specific language governing permissions and limitations under
// the License.
#pragma once
#include <cstddef>
#include "pw_kvs/alignment.h"
#include "pw_span/span.h"
#include "pw_status/status.h"
namespace pw::kvs {
class ChecksumAlgorithm {
// Resets the checksum to its initial state.
virtual void Reset() = 0;
// Updates the checksum with the provided data.
virtual void Update(span<const std::byte> data) = 0;
// Updates the checksum from a pointer and size.
void Update(const void* data, size_t size_bytes) {
return Update(span(static_cast<const std::byte*>(data), size_bytes));
// Returns the final result of the checksum. Update() can no longer be called
// after this. The returned span is valid until a call to Reset().
// Finish MUST be called before calling Verify.
span<const std::byte> Finish() {
Finalize(); // Implemented by derived classes, if required.
return state();
// Returns the size of the checksum state.
constexpr size_t size_bytes() const { return state_.size(); }
// Compares a calculated checksum to this checksum's state. The checksum must
// be at least as large as size_bytes(). If it is larger, bytes beyond
// size_bytes() are ignored.
// Finish MUST be called before calling Verify.
Status Verify(span<const std::byte> checksum) const;
// A derived class provides a span of its state buffer.
constexpr ChecksumAlgorithm(span<const std::byte> state) : state_(state) {}
// Protected destructor prevents deleting ChecksumAlgorithms from the base
// class, so that it is safe to have a non-virtual destructor.
~ChecksumAlgorithm() = default;
// Returns the current checksum state.
constexpr span<const std::byte> state() const { return state_; }
// Checksums that require finalizing operations may override this method.
virtual void Finalize() {}
span<const std::byte> state_;
// Calculates a checksum in kAlignmentBytes chunks. Checksum classes can inherit
// from this and implement UpdateAligned and FinalizeAligned instead of Update
// and Finalize.
template <size_t kAlignmentBytes, size_t kBufferSize = kAlignmentBytes>
class AlignedChecksum : public ChecksumAlgorithm {
void Update(span<const std::byte> data) final { writer_.Write(data); }
constexpr AlignedChecksum(span<const std::byte> state)
: ChecksumAlgorithm(state),
writer_(kAlignmentBytes, output_) {}
~AlignedChecksum() = default;
static_assert(kBufferSize >= kAlignmentBytes);
void Finalize() final {
virtual void UpdateAligned(span<const std::byte> data) = 0;
virtual void FinalizeAligned() = 0;
OutputToMethod<&AlignedChecksum::UpdateAligned> output_;
AlignedWriterBuffer<kBufferSize> writer_;
} // namespace pw::kvs