Function ComputeRoundingDelta

cpp/src/gandiva/precompiled/decimal_ops.cc:564–612

Compute the rounding delta for the given rounding type.

// Compute the rounding delta for the given rounding type.
static int32_t ComputeRoundingDelta(const BasicDecimal128& x, int32_t x_scale,
                                    int32_t out_scale, RoundType type) {
  if (type == kRoundTypeTrunc ||  // no rounding for this type.
      out_scale >= x_scale) {     // no digits dropped, so no rounding.
    return 0;
  }

  int32_t result = 0;
  switch (type) {
    case kRoundTypeHalfRoundUp: {
      auto base = BasicDecimal128::GetScaleMultiplier(x_scale - out_scale);
      auto trailing = x % base;
      if (trailing == 0) {
        result = 0;
      } else if (trailing.Abs() < base / 2) {
        result = 0;
      } else {
        result = (x < 0) ? -1 : 1;
      }
      break;
    }

    case kRoundTypeCeil:
      if (x < 0) {
        // no rounding for -ve
        result = 0;
      } else {
        auto base = BasicDecimal128::GetScaleMultiplier(x_scale - out_scale);
        auto trailing = x % base;
        result = (trailing == 0) ? 0 : 1;
      }
      break;

    case kRoundTypeFloor:
      if (x > 0) {
        // no rounding for +ve
        result = 0;
      } else {
        auto base = BasicDecimal128::GetScaleMultiplier(x_scale - out_scale);
        auto trailing = x % base;
        result = (trailing == 0) ? 0 : -1;
      }
      break;

    case kRoundTypeTrunc:
      break;
  }
  return result;
}

// Modify the scale and round.
static BasicDecimal128 RoundWithPositiveScale(const BasicDecimalScalar128& x,