133 lines
4.5 KiB
C++
133 lines
4.5 KiB
C++
// Copyright 2021 The Tint Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#include "fuzzers/random_generator.h"
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#include <algorithm>
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#include <cassert>
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#include <vector>
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#include "src/utils/hash.h"
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namespace tint {
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namespace fuzzers {
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namespace {
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/// Generate integer from uniform distribution
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/// @tparam I - integer type
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/// @param engine - random number engine to use
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/// @param lower - Lower bound of integer generated
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/// @param upper - Upper bound of integer generated
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/// @returns i, where lower <= i < upper
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template <typename I>
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I RandomUInt(std::mt19937_64* engine, I lower, I upper) {
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assert(lower < upper && "|lower| must be stictly less than |upper|");
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return std::uniform_int_distribution<I>(lower, upper - 1)(*engine);
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}
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/// Calculate the hash for the contents of a c-style data buffer
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/// This is intentionally not implemented as a generic override of HashCombine
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/// in "src/utils/hash.h", because it conflicts with the vardiac override for
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/// the case where a pointer and an integer are being hashed.
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/// @param data - pointer to buffer to be hashed
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/// @param size - number of elements in buffer
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/// @returns hash of the data in the buffer
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size_t HashBuffer(const uint8_t* data, const size_t size) {
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size_t hash = 102931;
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utils::HashCombine(&hash, size);
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for (size_t i = 0; i < size; i++) {
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utils::HashCombine(&hash, data[i]);
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}
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return hash;
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}
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} // namespace
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RandomGenerator::RandomGenerator(uint64_t seed) : engine_(seed) {}
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RandomGenerator::RandomGenerator(const uint8_t* data, size_t size)
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: engine_(RandomGenerator::CalculateSeed(data, size)) {}
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uint32_t RandomGenerator::GetUInt32(uint32_t lower, uint32_t upper) {
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return RandomUInt(&engine_, lower, upper);
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}
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uint32_t RandomGenerator::GetUInt32(uint32_t bound) {
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assert(bound > 0 && "|bound| must be greater than 0");
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return RandomUInt(&engine_, 0u, bound);
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}
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uint64_t RandomGenerator::GetUInt64(uint64_t lower, uint64_t upper) {
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return RandomUInt(&engine_, lower, upper);
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}
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uint64_t RandomGenerator::GetUInt64(uint64_t bound) {
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assert(bound > 0 && "|bound| must be greater than 0");
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return RandomUInt(&engine_, static_cast<uint64_t>(0), bound);
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}
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uint8_t RandomGenerator::GetByte() {
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return std::independent_bits_engine<std::mt19937_64, 8, uint8_t>(engine_)();
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}
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uint32_t RandomGenerator::Get4Bytes() {
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return std::independent_bits_engine<std::mt19937_64, 32, uint32_t>(engine_)();
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}
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void RandomGenerator::GetNBytes(uint8_t* dest, size_t n) {
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assert(dest && "|dest| must not be nullptr");
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std::generate(
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dest, dest + n,
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std::independent_bits_engine<std::mt19937_64, 8, uint8_t>(engine_));
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}
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bool RandomGenerator::GetBool() {
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return RandomUInt(&engine_, 0u, 2u);
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}
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bool RandomGenerator::GetWeightedBool(uint32_t percentage) {
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static const uint32_t kMaxPercentage = 100;
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assert(percentage <= kMaxPercentage &&
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"|percentage| needs to be within [0, 100]");
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return RandomUInt(&engine_, 0u, kMaxPercentage) < percentage;
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}
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uint64_t RandomGenerator::CalculateSeed(const uint8_t* data, size_t size) {
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assert(data != nullptr && "|data| must be !nullptr");
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// Number of bytes we want to skip at the start of data for the hash.
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// Fewer bytes may be skipped when `size` is small.
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// Has lower precedence than kHashDesiredMinBytes.
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static const int64_t kHashDesiredLeadingSkipBytes = 5;
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// Minimum number of bytes we want to use in the hash.
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// Used for short buffers.
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static const int64_t kHashDesiredMinBytes = 4;
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// Maximum number of bytes we want to use in the hash.
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static const int64_t kHashDesiredMaxBytes = 32;
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int64_t size_i64 = static_cast<int64_t>(size);
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int64_t hash_begin_i64 =
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std::min(kHashDesiredLeadingSkipBytes,
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std::max<int64_t>(size_i64 - kHashDesiredMinBytes, 0));
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int64_t hash_end_i64 =
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std::min(hash_begin_i64 + kHashDesiredMaxBytes, size_i64);
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size_t hash_begin = static_cast<size_t>(hash_begin_i64);
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size_t hash_size = static_cast<size_t>(hash_end_i64) - hash_begin;
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return HashBuffer(data + hash_begin, hash_size);
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}
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} // namespace fuzzers
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} // namespace tint
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