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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 "fuzzers/random_generator.h"
#include <algorithm>
#include <cassert>
#include <vector>
#include "src/utils/hash.h"
namespace tint {
namespace fuzzers {
namespace {
/// Generate integer from uniform distribution
/// @tparam I - integer type
/// @param engine - random number engine to use
/// @param lower - Lower bound of integer generated
/// @param upper - Upper bound of integer generated
/// @returns i, where lower <= i < upper
template <typename I>
I RandomUInt(std::mt19937_64* engine, I lower, I upper) {
assert(lower < upper && "|lower| must be stictly less than |upper|");
return std::uniform_int_distribution<I>(lower, upper - 1)(*engine);
}
/// 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/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 = 102931;
utils::HashCombine(&hash, size);
for (size_t i = 0; i < size; i++) {
utils::HashCombine(&hash, data[i]);
}
return hash;
}
} // namespace
RandomGenerator::RandomGenerator(uint64_t seed) : engine_(seed) {}
RandomGenerator::RandomGenerator(const uint8_t* data, size_t size)
: engine_(RandomGenerator::CalculateSeed(data, size)) {}
uint32_t RandomGenerator::GetUInt32(uint32_t lower, uint32_t upper) {
return RandomUInt(&engine_, lower, upper);
}
uint32_t RandomGenerator::GetUInt32(uint32_t bound) {
assert(bound > 0 && "|bound| must be greater than 0");
return RandomUInt(&engine_, 0u, bound);
}
uint64_t RandomGenerator::GetUInt64(uint64_t lower, uint64_t upper) {
return RandomUInt(&engine_, lower, upper);
}
uint64_t RandomGenerator::GetUInt64(uint64_t bound) {
assert(bound > 0 && "|bound| must be greater than 0");
return RandomUInt(&engine_, static_cast<uint64_t>(0), bound);
}
uint8_t RandomGenerator::GetByte() {
return std::independent_bits_engine<std::mt19937_64, 8, uint8_t>(engine_)();
}
uint32_t RandomGenerator::Get4Bytes() {
return std::independent_bits_engine<std::mt19937_64, 32, uint32_t>(engine_)();
}
void RandomGenerator::GetNBytes(uint8_t* dest, size_t n) {
assert(dest && "|dest| must not be nullptr");
std::generate(
dest, dest + n,
std::independent_bits_engine<std::mt19937_64, 8, uint8_t>(engine_));
}
bool RandomGenerator::GetBool() {
return RandomUInt(&engine_, 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 RandomUInt(&engine_, 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;
int64_t size_i64 = static_cast<int64_t>(size);
int64_t hash_begin_i64 =
std::min(kHashDesiredLeadingSkipBytes,
std::max<int64_t>(size_i64 - kHashDesiredMinBytes, 0));
int64_t hash_end_i64 =
std::min(hash_begin_i64 + kHashDesiredMaxBytes, size_i64);
size_t hash_begin = static_cast<size_t>(hash_begin_i64);
size_t hash_size = static_cast<size_t>(hash_end_i64) - hash_begin;
return HashBuffer(data + hash_begin, hash_size);
}
} // namespace fuzzers
} // namespace tint