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// Copyright 2021 The Tint 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
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// 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.
#include "src/tint/fuzzers/random_generator.h"
#include <algorithm>
#include <cassert>
#include <utility>
#include "src/tint/fuzzers/mersenne_twister_engine.h"
#include "src/tint/fuzzers/random_generator_engine.h"
#include "src/tint/utils/hash.h"
namespace tint::fuzzers {
namespace {
/// Calculate the hash for the contents of a c-style data buffer
/// This is intentionally not implemented as a generic override of HashCombine
/// in "src/tint/utils/hash.h", because it conflicts with the vardiac override
/// for the case where a pointer and an integer are being hashed.
/// @param data - pointer to buffer to be hashed
/// @param size - number of elements in buffer
/// @returns hash of the data in the buffer
size_t HashBuffer(const uint8_t* data, const size_t size) {
size_t hash = utils::Hash(size);
for (size_t i = 0; i < size; i++) {
hash = utils::HashCombine(hash, data[i]);
}
return hash;
}
} // namespace
RandomGenerator::RandomGenerator(std::unique_ptr<RandomGeneratorEngine> engine)
: engine_(std::move(engine)) {}
RandomGenerator::RandomGenerator(uint64_t seed)
: RandomGenerator(std::make_unique<MersenneTwisterEngine>(seed)) {}
uint32_t RandomGenerator::GetUInt32(uint32_t lower, uint32_t upper) {
assert(lower < upper && "|lower| must be strictly less than |upper|");
return engine_->RandomUInt32(lower, upper);
}
uint32_t RandomGenerator::GetUInt32(uint32_t bound) {
assert(bound > 0 && "|bound| must be greater than 0");
return engine_->RandomUInt32(0u, bound);
}
uint64_t RandomGenerator::GetUInt64(uint64_t lower, uint64_t upper) {
assert(lower < upper && "|lower| must be strictly less than |upper|");
return engine_->RandomUInt64(lower, upper);
}
uint64_t RandomGenerator::GetUInt64(uint64_t bound) {
assert(bound > 0 && "|bound| must be greater than 0");
return engine_->RandomUInt64(static_cast<uint64_t>(0), bound);
}
uint8_t RandomGenerator::GetByte() {
uint8_t result;
engine_->RandomNBytes(&result, 1);
return result;
}
uint32_t RandomGenerator::Get4Bytes() {
uint32_t result;
engine_->RandomNBytes(reinterpret_cast<uint8_t*>(&result), 4);
return result;
}
void RandomGenerator::GetNBytes(uint8_t* dest, size_t n) {
assert(dest && "|dest| must not be nullptr");
engine_->RandomNBytes(dest, n);
}
bool RandomGenerator::GetBool() {
return engine_->RandomUInt32(0u, 2u);
}
bool RandomGenerator::GetWeightedBool(uint32_t percentage) {
static const uint32_t kMaxPercentage = 100;
assert(percentage <= kMaxPercentage && "|percentage| needs to be within [0, 100]");
return engine_->RandomUInt32(0u, kMaxPercentage) < percentage;
}
uint64_t RandomGenerator::CalculateSeed(const uint8_t* data, size_t size) {
assert(data != nullptr && "|data| must be !nullptr");
// Number of bytes we want to skip at the start of data for the hash.
// Fewer bytes may be skipped when `size` is small.
// Has lower precedence than kHashDesiredMinBytes.
static const int64_t kHashDesiredLeadingSkipBytes = 5;
// Minimum number of bytes we want to use in the hash.
// Used for short buffers.
static const int64_t kHashDesiredMinBytes = 4;
// Maximum number of bytes we want to use in the hash.
static const int64_t kHashDesiredMaxBytes = 32;
auto size_i64 = static_cast<int64_t>(size);
auto hash_begin_i64 = std::min(kHashDesiredLeadingSkipBytes,
std::max<int64_t>(size_i64 - kHashDesiredMinBytes, 0));
auto hash_end_i64 = std::min(hash_begin_i64 + kHashDesiredMaxBytes, size_i64);
auto hash_begin = static_cast<size_t>(hash_begin_i64);
auto hash_size = static_cast<size_t>(hash_end_i64) - hash_begin;
return HashBuffer(data + hash_begin, hash_size);
}
} // namespace tint::fuzzers