Function randPrecisionScale

bolt/vector/fuzzer/VectorFuzzer.cpp:176–222

Generate a random precision in range [minPrecision, maxPrecision] and a scale in range [0, random precision generated]. @param maximum precision.

/// and a scale in range [0, random precision generated].
/// @param maximum precision.
std::pair<int8_t, int8_t> randPrecisionScale(
    FuzzerGenerator& rng,
    int8_t minPrecision,
    int8_t maxPrecision) {
  struct DecimalSpec {
    std::optional<int8_t> precision;
    std::optional<int8_t> scale;
  };

  using SpecialDecimalSpecs = std::unordered_map<std::string, DecimalSpec>;
  SpecialDecimalSpecs specialDecimalSpecs = {
      {"MAX_REPRESENTABLE", {maxPrecision, 0}},
      {"MIN_REPRESENTABLE", {maxPrecision, 0}},
      {"VERY_HIGH_PRECISION", {maxPrecision, std::nullopt}},
      {"VERY_LONG_FRACTION", {maxPrecision, maxPrecision}},
      {"LARGEST_PRECISION_LARGEST_SCALE", {maxPrecision, maxPrecision}},
      {"LARGEST_PRECISION_SMALLEST_SCALE", {maxPrecision, 0}},
      {"SMALLEST_PRECISION_LARGEST_SCALE", {minPrecision, minPrecision}},
      {"SMALLEST_PRECISION_SMALLEST_SCALE", {minPrecision, 0}}};
  size_t numSpecialDecimalSpecs = specialDecimalSpecs.size();

  auto isSpecial = rand<bool>(rng);
  if (isSpecial) {
    // Randomly select from predefined special precisions and scales.
    auto index = rand<size_t>(rng) % numSpecialDecimalSpecs;
    auto iteratorSpecialDecimalSpecs = specialDecimalSpecs.begin();
    std::advance(iteratorSpecialDecimalSpecs, index);
    const auto& [specialDecimalName, specialDecimalSpec] =
        *iteratorSpecialDecimalSpecs;
    if (specialDecimalSpec.scale.has_value()) {
      return std::make_pair(
          *specialDecimalSpec.precision, *specialDecimalSpec.scale);
    }

    // If the scale is std::nullopt, generate a scale in range [0, precision].
    auto scale = rand<int8_t>(rng) % (*specialDecimalSpec.precision + 1);
    return std::make_pair(*specialDecimalSpec.precision, scale);
  }

  // Purely random generation.
  // Generate precision in range [min precision, max precision].
  auto precision =
      minPrecision + (rand<int8_t>(rng) % (maxPrecision - minPrecision + 1));
  // Generate scale in range [0, precision].
  auto scale = rand<int8_t>(rng) % (precision + 1);
  return {precision, scale};
}

// Generate a short decimal TypePtr with random / special precision and scale.
inline TypePtr randShortDecimalType(FuzzerGenerator& rng) {