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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 <cstdint>
#include <span>
#include "pw_bytes/span.h"
#include "pw_status/status_with_size.h"
namespace pw::random {
// A random generator uses injected entropy to generate random values. Many of
// the guarantees for this interface are provided at the level of the
// implementations. In general:
// * DO NOT assume a generator is cryptographically secure.
// * DO NOT assume uniformity of generated data.
// * DO assume a generator can be exhausted.
class RandomGenerator {
virtual ~RandomGenerator() = default;
template <class T>
StatusWithSize GetInt(T& dest) {
"Use Get() for non-integral types");
return Get({reinterpret_cast<std::byte*>(&dest), sizeof(T)});
// Populates the destination buffer with a randomly generated value. Returns:
// OK - Successfully filled the destination buffer with random data.
// RESOURCE_EXHAUSTED - Filled the buffer with the returned number of bytes.
// The returned size is number of complete bytes with random data.
virtual StatusWithSize Get(ByteSpan dest) = 0;
// Injects entropy into the pool. `data` may have up to 32 bits of random
// entropy. If the number of bits of entropy is less than 32, entropy is
// assumed to be stored in the least significant bits of `data`.
virtual void InjectEntropyBits(uint32_t data, uint_fast8_t num_bits) = 0;
// Injects entropy into the pool byte-by-byte.
void InjectEntropy(ConstByteSpan data) {
for (std::byte b : data) {
InjectEntropyBits(std::to_integer<uint32_t>(b), /*num_bits=*/8);
} // namespace pw::random