chore: use int128_t calculation

Author: zhjwpku

src/iceberg/util/decimal.cc

@@ -356,12 +356,7 @@ Decimal::Decimal(std::string_view str) {
 }
 
 Decimal& Decimal::Negate() {
-  uint64_t result_low = ~low() + 1;
-  int64_t result_high = ~high();
-  if (result_low == 0) {
-    result_high = SafeSignedAdd<int64_t>(result_high, 1);
-  }
-  *this = Decimal(result_high, result_low);
+  data_ = ~data_ + 1;
   return *this;
 }
 
@@ -373,35 +368,17 @@ Decimal Decimal::Abs(const Decimal& value) {
 }
 
 Decimal& Decimal::operator+=(const Decimal& other) {
-  int64_t result_high = SafeSignedAdd(high(), other.high());
-  uint64_t result_low = low() + other.low();
-  result_high = SafeSignedAdd<int64_t>(result_high, result_low < low());
-  *this = Decimal(result_high, result_low);
+  data_ += other.data_;
   return *this;
 }
 
 Decimal& Decimal::operator-=(const Decimal& other) {
-  int64_t result_high = SafeSignedSubtract(high(), other.high());
-  uint64_t result_low = low() - other.low();
-  result_high = SafeSignedSubtract<int64_t>(result_high, result_low > low());
-  *this = Decimal(result_high, result_low);
+  data_ -= other.data_;
   return *this;
 }
 
 Decimal& Decimal::operator*=(const Decimal& other) {
-  // Since the max value of Decimal is supposed to be 1e38 - 1 and the min the
-  // negation taking the abosolute values here should aways be safe.
-  const bool negate = Sign() != other.Sign();
-  Decimal x = Decimal::Abs(*this);
-  Decimal y = Decimal::Abs(other);
-
-  Uint128 r(x);
-  r *= Uint128(y);
-
-  *this = Decimal(static_cast<int64_t>(r.high()), r.low());
-  if (negate) {
-    Negate();
-  }
+  data_ *= other.data_;
   return *this;
 }
 
@@ -412,9 +389,7 @@ Result<std::pair<Decimal, Decimal>> Decimal::Divide(const Decimal& divisor) cons
 }
 
 Decimal& Decimal::operator/=(const Decimal& other) {
-  Decimal remainder;
-  auto s = DecimalDivide(*this, other, this, &remainder);
-  assert(s);
+  data_ /= other.data_;
   return *this;
 }
 

src/iceberg/util/decimal.h

@@ -54,6 +54,10 @@ class ICEBERG_EXPORT Decimal {
   /// \brief Default constructor initializes to zero.
   constexpr Decimal() noexcept = default;
 
+  /// \brief Create a Decimal from a 128-bit integer.
+  constexpr Decimal(int128_t value) noexcept  // NOLINT
+      : data_(value) {}
+
   /// \brief Create a Decimal from any integer not wider than 64 bits.
   template <typename T>
     requires(std::is_integral_v<T> && (sizeof(T) <= sizeof(uint64_t)))