[compiler-rt] Refactor FuzzedDataProvider for better readability.

[Dor1s]

updated CL description

[Dor1s]

The failure seems to be clang-tidy again -- I'm not going to change names of the methods. PTAL at lines 37-78, if you find time. The rest is existing code moved out of the class definition block. If no one takes a look, I'll land it in a couple days anyways, no worries.

[hctim]

LGTM w/ one nit

compiler-rt/include/fuzzer/FuzzedDataProvider.h

63

Might be worth adding a comment here that probability is just a float between 0 and 1 [inclusive].

72

Speaking of, is it worth having a std::vector<const T> variant of this?

[Dor1s]

rebase + add a comment for ConsumeProbability

[Dor1s]

thanks, Mitch!

compiler-rt/include/fuzzer/FuzzedDataProvider.h

63

done

72

sounds reasonable, although a version with two iterators (.begin(), .end()) might be even better, but that's out of the scope of this CL

[leonardchan]

Hi. I think this patch might be leading to the linker error we're seeing:

>>> defined at FuzzedDataProvider.h:283 (/b/s/w/ir/k/recipe_cleanup/clangKqmrKj/lib/clang/11.0.0/include/fuzzer/FuzzedDataProvider.h:283)
>>>            obj/zircon/system/ulib/fs/journal/test/journal-replay-fuzzer_test.replay_fuzztest.cc.o:(FuzzedDataProvider::ConsumeBool())
>>> defined at FuzzedDataProvider.h:283 (/b/s/w/ir/k/recipe_cleanup/clangKqmrKj/lib/clang/11.0.0/include/fuzzer/FuzzedDataProvider.h:283)
>>>            obj/zircon/system/ulib/fs/journal/test/fuzz-utils.fuzzer_utils.cc.o:(.text+0x3F0)

ld.lld: error: duplicate symbol: FuzzedDataProvider::ConsumeData(void*, unsigned long)
>>> defined at FuzzedDataProvider.h:318 (/b/s/w/ir/k/recipe_cleanup/clangKqmrKj/lib/clang/11.0.0/include/fuzzer/FuzzedDataProvider.h:318)
>>>            obj/zircon/system/ulib/fs/journal/test/journal-replay-fuzzer_test.replay_fuzztest.cc.o:(FuzzedDataProvider::ConsumeData(void*, unsigned long))
>>> defined at FuzzedDataProvider.h:318 (/b/s/w/ir/k/recipe_cleanup/clangKqmrKj/lib/clang/11.0.0/include/fuzzer/FuzzedDataProvider.h:318)
>>>            obj/zircon/system/ulib/fs/journal/test/fuzz-utils.fuzzer_utils.cc.o:(.text+0x420)

... a bunch more

Would you mind taking a look? Thanks.

Builder: https://ci.chromium.org/p/fuchsia/builders/ci/clang_toolchain.fuchsia-x64-debug-subbuild/b8884854137402901888

[Dor1s]

In D76651#1941953, @leonardchan wrote:

Hi. I think this patch might be leading to the linker error we're seeing:

>>> defined at FuzzedDataProvider.h:283 (/b/s/w/ir/k/recipe_cleanup/clangKqmrKj/lib/clang/11.0.0/include/fuzzer/FuzzedDataProvider.h:283)
>>>            obj/zircon/system/ulib/fs/journal/test/journal-replay-fuzzer_test.replay_fuzztest.cc.o:(FuzzedDataProvider::ConsumeBool())
>>> defined at FuzzedDataProvider.h:283 (/b/s/w/ir/k/recipe_cleanup/clangKqmrKj/lib/clang/11.0.0/include/fuzzer/FuzzedDataProvider.h:283)
>>>            obj/zircon/system/ulib/fs/journal/test/fuzz-utils.fuzzer_utils.cc.o:(.text+0x3F0)

ld.lld: error: duplicate symbol: FuzzedDataProvider::ConsumeData(void*, unsigned long)
>>> defined at FuzzedDataProvider.h:318 (/b/s/w/ir/k/recipe_cleanup/clangKqmrKj/lib/clang/11.0.0/include/fuzzer/FuzzedDataProvider.h:318)
>>>            obj/zircon/system/ulib/fs/journal/test/journal-replay-fuzzer_test.replay_fuzztest.cc.o:(FuzzedDataProvider::ConsumeData(void*, unsigned long))
>>> defined at FuzzedDataProvider.h:318 (/b/s/w/ir/k/recipe_cleanup/clangKqmrKj/lib/clang/11.0.0/include/fuzzer/FuzzedDataProvider.h:318)
>>>            obj/zircon/system/ulib/fs/journal/test/fuzz-utils.fuzzer_utils.cc.o:(.text+0x420)

... a bunch more

Would you mind taking a look? Thanks.

Builder: https://ci.chromium.org/p/fuchsia/builders/ci/clang_toolchain.fuchsia-x64-debug-subbuild/b8884854137402901888

Thank you, looking.

[Dor1s]

@leonardchan I've committed https://github.com/llvm/llvm-project/commit/6d0488f75bb2f37bcfe93fc8f59f6e78c9a0c939, that should help, I'll monitor the buildbot.

[leonardchan]

In D76651#1942163, @Dor1s wrote:

@leonardchan I've committed https://github.com/llvm/llvm-project/commit/6d0488f75bb2f37bcfe93fc8f59f6e78c9a0c939, that should help, I'll monitor the buildbot.

Thanks for the update! Looks to be green now.

compiler-rt/include/fuzzer/FuzzedDataProvider.h

 #include <string>
 #include <type_traits>
 #include <utility>
 #include <vector>
 
 // In addition to the comments below, the API is also briefly documented at
 // https://github.com/google/fuzzing/blob/master/docs/split-inputs.md#fuzzed-data-provider
 class FuzzedDataProvider {
- public:
   // |data| is an array of length |size| that the FuzzedDataProvider wraps to
   // provide more granular access. |data| must outlive the FuzzedDataProvider.
   FuzzedDataProvider(const uint8_t *data, size_t size)
       : data_ptr_(data), remaining_bytes_(size) {}
   ~FuzzedDataProvider() = default;
 
-  // Returns a std::vector containing |num_bytes| of input data. If fewer than
-  // |num_bytes| of data remain, returns a shorter std::vector containing all
-  // of the data that's left. Can be used with any byte sized type, such as
-  // char, unsigned char, uint8_t, etc.
-  template <typename T> std::vector<T> ConsumeBytes(size_t num_bytes) {
-    num_bytes = std::min(num_bytes, remaining_bytes_);
-    return ConsumeBytes<T>(num_bytes, num_bytes);
-  }
+  // See the implementation below (after the class definition) for more verbose
+  // comments for each of the methods.
+
+  // Methods returning std::vector of bytes. These are the most popular choice
+  // when splitting fuzzing input into pieces, as every piece is put into a
+  // separate buffer (i.e. ASan would catch any under-/overflow) and the memory
+  // will be released automatically.
+  template <typename T> std::vector<T> ConsumeBytes(size_t num_bytes);
+  template <typename T>
+  std::vector<T> ConsumeBytesWithTerminator(size_t num_bytes, T terminator = 0);
+  template <typename T> std::vector<T> ConsumeRemainingBytes();
+
+  // Methods returning strings. Use only when you need a std::string or a null
+  // terminated C-string. Otherwise, prefer the methods returning std::vector.
+  std::string ConsumeBytesAsString(size_t num_bytes);
+  std::string ConsumeRandomLengthString(size_t max_length);
+  std::string ConsumeRandomLengthString();
+  std::string ConsumeRemainingBytesAsString();
+
+  // Methods returning integer values.
+  template <typename T> T ConsumeIntegral();
+  template <typename T> T ConsumeIntegralInRange(T min, T max);
+
+  // Methods returning floating point values.
+  template <typename T> T ConsumeFloatingPoint();
+  template <typename T> T ConsumeFloatingPointInRange(T min, T max);
+  template <typename T> T ConsumeProbability();
+
+  bool ConsumeBool();
+
+  // Returns a value chosen from the given enum.
+  template <typename T> T ConsumeEnum();
+
+  // Returns a value from the given array.
+  template <typename T, size_t size> T PickValueInArray(const T (&array)[size]);
+  template <typename T> T PickValueInArray(std::initializer_list<const T> list);
+
+  // Writes data to the given destination and returns number of bytes written.
+  size_t ConsumeData(void *destination, size_t num_bytes);
+
+  // Reports the remaining bytes available for fuzzed input.
+  size_t remaining_bytes() { return remaining_bytes_; }
+
+private:
+  FuzzedDataProvider(const FuzzedDataProvider &) = delete;
+  FuzzedDataProvider &operator=(const FuzzedDataProvider &) = delete;
+
+  void CopyAndAdvance(void *destination, size_t num_bytes);
+
+  void Advance(size_t num_bytes);
+
+  template <typename T>
+  std::vector<T> ConsumeBytes(size_t size, size_t num_bytes);
+
+  template <typename TS, typename TU> TS ConvertUnsignedToSigned(TU value);
+
+  const uint8_t *data_ptr_;
+  size_t remaining_bytes_;
+};
+
+template <typename T>
+std::vector<T> FuzzedDataProvider::ConsumeBytes(size_t num_bytes) {
 
-  // Similar to |ConsumeBytes|, but also appends the terminator value at the end
-  // of the resulting vector. Useful, when a mutable null-terminated C-string is
-  // needed, for example. But that is a rare case. Better avoid it, if possible,
-  // and prefer using |ConsumeBytes| or |ConsumeBytesAsString| methods.
-  template <typename T>
-  std::vector<T> ConsumeBytesWithTerminator(size_t num_bytes,
-                                            T terminator = 0) {
-    num_bytes = std::min(num_bytes, remaining_bytes_);
-    std::vector<T> result = ConsumeBytes<T>(num_bytes + 1, num_bytes);
-    result.back() = terminator;
-    return result;
-  }
+std::vector<T> FuzzedDataProvider::ConsumeBytesWithTerminator(size_t num_bytes,
+                                                              T terminator) {
 
-  // Returns a std::string containing |num_bytes| of input data. Using this and
-  // |.c_str()| on the resulting string is the best way to get an immutable
-  // null-terminated C string. If fewer than |num_bytes| of data remain, returns
-  // a shorter std::string containing all of the data that's left.
-  std::string ConsumeBytesAsString(size_t num_bytes) {
-    static_assert(sizeof(std::string::value_type) == sizeof(uint8_t),
-                  "ConsumeBytesAsString cannot convert the data to a string.");
+// Returns a std::vector containing all remaining bytes of the input data.
+template <typename T>
+std::vector<T> FuzzedDataProvider::ConsumeRemainingBytes() {
+  return ConsumeBytes<T>(remaining_bytes_);
+}
+
+std::string FuzzedDataProvider::ConsumeBytesAsString(size_t num_bytes) {
 
-    num_bytes = std::min(num_bytes, remaining_bytes_);
-    std::string result(
-        reinterpret_cast<const std::string::value_type *>(data_ptr_),
-        num_bytes);
-    Advance(num_bytes);
-    return result;
-  }
+      reinterpret_cast<const std::string::value_type *>(data_ptr_), num_bytes);
 
-  // Returns a number in the range [min, max] by consuming bytes from the
-  // input data. The value might not be uniformly distributed in the given
-  // range. If there's no input data left, always returns |min|. |min| must
-  // be less than or equal to |max|.
-  template <typename T> T ConsumeIntegralInRange(T min, T max) {
-    static_assert(std::is_integral<T>::value, "An integral type is required.");
-    static_assert(sizeof(T) <= sizeof(uint64_t), "Unsupported integral type.");
-
-    if (min > max)
-      abort();
-
-    // Use the biggest type possible to hold the range and the result.
-    uint64_t range = static_cast<uint64_t>(max) - min;
-    uint64_t result = 0;
-    size_t offset = 0;
-
-    while (offset < sizeof(T) * CHAR_BIT && (range >> offset) > 0 &&
-           remaining_bytes_ != 0) {
-      // Pull bytes off the end of the seed data. Experimentally, this seems to
-      // allow the fuzzer to more easily explore the input space. This makes
-      // sense, since it works by modifying inputs that caused new code to run,
-      // and this data is often used to encode length of data read by
-      // |ConsumeBytes|. Separating out read lengths makes it easier modify the
-      // contents of the data that is actually read.
-      --remaining_bytes_;
-      result = (result << CHAR_BIT) | data_ptr_[remaining_bytes_];
-      offset += CHAR_BIT;
-    }
-
-    // Avoid division by 0, in case |range + 1| results in overflow.
-    if (range != std::numeric_limits<decltype(range)>::max())
-      result = result % (range + 1);
-
-    return static_cast<T>(min + result);
-  }
-
-  // Returns a std::string of length from 0 to |max_length|. When it runs out of
-  // input data, returns what remains of the input. Designed to be more stable
-  // with respect to a fuzzer inserting characters than just picking a random
-  // length and then consuming that many bytes with |ConsumeBytes|.
-  std::string ConsumeRandomLengthString(size_t max_length) {
-    // Reads bytes from the start of |data_ptr_|. Maps "\\" to "\", and maps "\"
-    // followed by anything else to the end of the string. As a result of this
-    // logic, a fuzzer can insert characters into the string, and the string
-    // will be lengthened to include those new characters, resulting in a more
-    // stable fuzzer than picking the length of a string independently from
-    // picking its contents.
-    std::string result;
+std::string FuzzedDataProvider::ConsumeRandomLengthString(size_t max_length) {
 
-    // Reserve the anticipated capaticity to prevent several reallocations.
-    result.reserve(std::min(max_length, remaining_bytes_));
-    for (size_t i = 0; i < max_length && remaining_bytes_ != 0; ++i) {
-      char next = ConvertUnsignedToSigned<char>(data_ptr_[0]);
-      Advance(1);
-      if (next == '\\' && remaining_bytes_ != 0) {
-        next = ConvertUnsignedToSigned<char>(data_ptr_[0]);
-        Advance(1);
-        if (next != '\\')
-          break;
-      }
-      result += next;
-    }
 
-    result.shrink_to_fit();
-    return result;
-  }
 
-  // Returns a std::string of length from 0 to |remaining_bytes_|.
-  std::string ConsumeRandomLengthString() {
-    return ConsumeRandomLengthString(remaining_bytes_);
-  }
+std::string FuzzedDataProvider::ConsumeRandomLengthString() {
 
-  // Returns a std::vector containing all remaining bytes of the input data.
-  template <typename T> std::vector<T> ConsumeRemainingBytes() {
-    return ConsumeBytes<T>(remaining_bytes_);
-  }
-
-  // Returns a std::string containing all remaining bytes of the input data.
-  // Prefer using |ConsumeRemainingBytes| unless you actually need a std::string
-  // object.
-  std::string ConsumeRemainingBytesAsString() {
-    return ConsumeBytesAsString(remaining_bytes_);
-  }
+std::string FuzzedDataProvider::ConsumeRemainingBytesAsString() {
 
-  // Returns a number in the range [Type's min, Type's max]. The value might
-  // not be uniformly distributed in the given range. If there's no input data
-  // left, always returns |min|.
-  template <typename T> T ConsumeIntegral() {
-    return ConsumeIntegralInRange(std::numeric_limits<T>::min(),
-                                  std::numeric_limits<T>::max());
-  }
+template <typename T> T FuzzedDataProvider::ConsumeIntegral() {
 
-  // Reads one byte and returns a bool, or false when no data remains.
-  bool ConsumeBool() { return 1 & ConsumeIntegral<uint8_t>(); }
-
-  // Returns a copy of the value selected from the given fixed-size |array|.
-  template <typename T, size_t size>
-  T PickValueInArray(const T (&array)[size]) {
-    static_assert(size > 0, "The array must be non empty.");
-    return array[ConsumeIntegralInRange<size_t>(0, size - 1)];
-  }
-
-  template <typename T>
-  T PickValueInArray(std::initializer_list<const T> list) {
-    // TODO(Dor1s): switch to static_assert once C++14 is allowed.
-    if (!list.size())
-      abort();
+// Returns a number in the range [min, max] by consuming bytes from the
+// input data. The value might not be uniformly distributed in the given
+// range. If there's no input data left, always returns |min|. |min| must
+// be less than or equal to |max|.
+T FuzzedDataProvider::ConsumeIntegralInRange(T min, T max) {
+  static_assert(std::is_integral<T>::value, "An integral type is required.");
+  static_assert(sizeof(T) <= sizeof(uint64_t), "Unsupported integral type.");
+
+  if (min > max)
 
-    return *(list.begin() + ConsumeIntegralInRange<size_t>(0, list.size() - 1));
-  }
+  // Use the biggest type possible to hold the range and the result.
+  uint64_t range = static_cast<uint64_t>(max) - min;
+  uint64_t result = 0;
+  size_t offset = 0;
 
-  // Returns an enum value. The enum must start at 0 and be contiguous. It must
-  // also contain |kMaxValue| aliased to its largest (inclusive) value. Such as:
-  // enum class Foo { SomeValue, OtherValue, kMaxValue = OtherValue };
-  template <typename T> T ConsumeEnum() {
-    static_assert(std::is_enum<T>::value, "|T| must be an enum type.");
-    return static_cast<T>(ConsumeIntegralInRange<uint32_t>(
-        0, static_cast<uint32_t>(T::kMaxValue)));
+  while (offset < sizeof(T) * CHAR_BIT && (range >> offset) > 0 &&
+         remaining_bytes_ != 0) {
+    // Pull bytes off the end of the seed data. Experimentally, this seems to
+    // allow the fuzzer to more easily explore the input space. This makes
+    // sense, since it works by modifying inputs that caused new code to run,
+    // and this data is often used to encode length of data read by
+    // |ConsumeBytes|. Separating out read lengths makes it easier modify the
+    // contents of the data that is actually read.
+    --remaining_bytes_;
+    result = (result << CHAR_BIT) | data_ptr_[remaining_bytes_];
+    offset += CHAR_BIT;
   }
 
-  // Returns a floating point number in the range [0.0, 1.0]. If there's no
-  // input data left, always returns 0.
-  template <typename T> T ConsumeProbability() {
-    static_assert(std::is_floating_point<T>::value,
-                  "A floating point type is required.");
-
-    // Use different integral types for different floating point types in order
-    // to provide better density of the resulting values.
-    using IntegralType =
-        typename std::conditional<(sizeof(T) <= sizeof(uint32_t)), uint32_t,
-                                  uint64_t>::type;
+  // Avoid division by 0, in case |range + 1| results in overflow.
+  if (range != std::numeric_limits<decltype(range)>::max())
+    result = result % (range + 1);
 
-    T result = static_cast<T>(ConsumeIntegral<IntegralType>());
-    result /= static_cast<T>(std::numeric_limits<IntegralType>::max());
-    return result;
-  }
+  return static_cast<T>(min + result);
 
-  // Returns a floating point value in the range [Type's lowest, Type's max] by
-  // consuming bytes from the input data. If there's no input data left, always
-  // returns approximately 0.
-  template <typename T> T ConsumeFloatingPoint() {
-    return ConsumeFloatingPointInRange<T>(std::numeric_limits<T>::lowest(),
-                                          std::numeric_limits<T>::max());
-  }
+template <typename T> T FuzzedDataProvider::ConsumeFloatingPoint() {
 
-  // Returns a floating point value in the given range by consuming bytes from
-  // the input data. If there's no input data left, returns |min|. Note that
-  // |min| must be less than or equal to |max|.
-  template <typename T> T ConsumeFloatingPointInRange(T min, T max) {
-    if (min > max)
-      abort();
+template <typename T>
+T FuzzedDataProvider::ConsumeFloatingPointInRange(T min, T max) {
 
-    T range = .0;
-    T result = min;
-    constexpr T zero(.0);
-    if (max > zero && min < zero && max > min + std::numeric_limits<T>::max()) {
-      // The diff |max - min| would overflow the given floating point type. Use
-      // the half of the diff as the range and consume a bool to decide whether
-      // the result is in the first of the second part of the diff.
-      range = (max / 2.0) - (min / 2.0);
-      if (ConsumeBool()) {
-        result += range;
-      }
-    } else {
-      range = max - min;
-    }
 
-    return result + range * ConsumeProbability<T>();
-  }
 
-  // Writes |num_bytes| of input data to the given destination pointer. If there
-  // is not enough data left, writes all remaining bytes. Return value is the
-  // number of bytes written.
-  // In general, it's better to avoid using this function, but it may be useful
-  // in cases when it's necessary to fill a certain buffer or object with
-  // fuzzing data.
-  size_t ConsumeData(void *destination, size_t num_bytes) {
-    num_bytes = std::min(num_bytes, remaining_bytes_);
-    CopyAndAdvance(destination, num_bytes);
-    return num_bytes;
-  }
+// Returns a floating point number in the range [0.0, 1.0]. If there's no
+// input data left, always returns 0.
+template <typename T> T FuzzedDataProvider::ConsumeProbability() {
+  static_assert(std::is_floating_point<T>::value,
+                "A floating point type is required.");
+
+  // Use different integral types for different floating point types in order
+  // to provide better density of the resulting values.
+  using IntegralType =
+      typename std::conditional<(sizeof(T) <= sizeof(uint32_t)), uint32_t,
+                                uint64_t>::type;
+
+  T result = static_cast<T>(ConsumeIntegral<IntegralType>());
+  result /= static_cast<T>(std::numeric_limits<IntegralType>::max());
+  return result;
+}
+
+// Reads one byte and returns a bool, or false when no data remains.
+bool FuzzedDataProvider::ConsumeBool() {
+  return 1 & ConsumeIntegral<uint8_t>();
+}
+
+// Returns an enum value. The enum must start at 0 and be contiguous. It must
+// also contain |kMaxValue| aliased to its largest (inclusive) value. Such as:
+// enum class Foo { SomeValue, OtherValue, kMaxValue = OtherValue };
+template <typename T> T FuzzedDataProvider::ConsumeEnum() {
+  static_assert(std::is_enum<T>::value, "|T| must be an enum type.");
+  return static_cast<T>(
+      ConsumeIntegralInRange<uint32_t>(0, static_cast<uint32_t>(T::kMaxValue)));
+}
+
+// Returns a copy of the value selected from the given fixed-size |array|.
+template <typename T, size_t size>
+T FuzzedDataProvider::PickValueInArray(const T (&array)[size]) {
+  static_assert(size > 0, "The array must be non empty.");
+  return array[ConsumeIntegralInRange<size_t>(0, size - 1)];
+}
+
+template <typename T>
+T FuzzedDataProvider::PickValueInArray(std::initializer_list<const T> list) {
+  // TODO(Dor1s): switch to static_assert once C++14 is allowed.
+  if (!list.size())
+    abort();
+
+  return *(list.begin() + ConsumeIntegralInRange<size_t>(0, list.size() - 1));
+}
+
+size_t FuzzedDataProvider::ConsumeData(void *destination, size_t num_bytes) {
 
-  // Reports the remaining bytes available for fuzzed input.
-  size_t remaining_bytes() { return remaining_bytes_; }
-
- private:
-  FuzzedDataProvider(const FuzzedDataProvider &) = delete;
-  FuzzedDataProvider &operator=(const FuzzedDataProvider &) = delete;
-
-  void CopyAndAdvance(void *destination, size_t num_bytes) {
-    std::memcpy(destination, data_ptr_, num_bytes);
-    Advance(num_bytes);
-  }
+// Private methods.
+void FuzzedDataProvider::CopyAndAdvance(void *destination, size_t num_bytes) {
 
-  void Advance(size_t num_bytes) {
-    if (num_bytes > remaining_bytes_)
-      abort();
+void FuzzedDataProvider::Advance(size_t num_bytes) {
 
-    data_ptr_ += num_bytes;
-    remaining_bytes_ -= num_bytes;
-  }
 
-  template <typename T>
-  std::vector<T> ConsumeBytes(size_t size, size_t num_bytes) {
-    static_assert(sizeof(T) == sizeof(uint8_t), "Incompatible data type.");
+std::vector<T> FuzzedDataProvider::ConsumeBytes(size_t size, size_t num_bytes) {
 
-    // The point of using the size-based constructor below is to increase the
-    // odds of having a vector object with capacity being equal to the length.
-    // That part is always implementation specific, but at least both libc++ and
-    // libstdc++ allocate the requested number of bytes in that constructor,
-    // which seems to be a natural choice for other implementations as well.
-    // To increase the odds even more, we also call |shrink_to_fit| below.
-    std::vector<T> result(size);
-    if (size == 0) {
-      if (num_bytes != 0)
-        abort();
-      return result;
-    }
 
-    CopyAndAdvance(result.data(), num_bytes);
 
-    // Even though |shrink_to_fit| is also implementation specific, we expect it
-    // to provide an additional assurance in case vector's constructor allocated
-    // a buffer which is larger than the actual amount of data we put inside it.
-    result.shrink_to_fit();
-    return result;
-  }
 
-  template <typename TS, typename TU> TS ConvertUnsignedToSigned(TU value) {
-    static_assert(sizeof(TS) == sizeof(TU), "Incompatible data types.");
-    static_assert(!std::numeric_limits<TU>::is_signed,
-                  "Source type must be unsigned.");
+template <typename TS, typename TU>
+TS FuzzedDataProvider::ConvertUnsignedToSigned(TU value) {
 
-    // TODO(Dor1s): change to `if constexpr` once C++17 becomes mainstream.
-    if (std::numeric_limits<TS>::is_modulo)
-      return static_cast<TS>(value);
 
-    // Avoid using implementation-defined unsigned to signed conversions.
-    // To learn more, see https://stackoverflow.com/questions/13150449.
-    if (value <= std::numeric_limits<TS>::max()) {
-      return static_cast<TS>(value);
-    } else {
-      constexpr auto TS_min = std::numeric_limits<TS>::min();
-      return TS_min + static_cast<char>(value - TS_min);
-    }
-  }
 
-  const uint8_t *data_ptr_;
-  size_t remaining_bytes_;
-};
-
 #endif // LLVM_FUZZER_FUZZED_DATA_PROVIDER_H_