pitrou commented on a change in pull request #8475:
URL: https://github.com/apache/arrow/pull/8475#discussion_r507832411
##########
File path: cpp/src/arrow/util/basic_decimal.cc
##########
@@ -775,4 +833,119 @@ int32_t BasicDecimal128::CountLeadingBinaryZeros() const {
}
}
+#if ARROW_LITTLE_ENDIAN
+BasicDecimal256::BasicDecimal256(const uint8_t* bytes)
+ : little_endian_array_(
+ std::array<uint64_t, 4>({reinterpret_cast<const uint64_t*>(bytes)[0],
+ reinterpret_cast<const uint64_t*>(bytes)[1],
+ reinterpret_cast<const uint64_t*>(bytes)[2],
+ reinterpret_cast<const
uint64_t*>(bytes)[3]})) {}
+#else
+BasicDecimal256::BasicDecimal256(const uint8_t* bytes)
+ : little_endian_array_(
+ std::array<uint64_t, 4>({reinterpret_cast<const uint64_t*>(bytes)[3],
+ reinterpret_cast<const uint64_t*>(bytes)[2],
+ reinterpret_cast<const uint64_t*>(bytes)[1],
+ reinterpret_cast<const
uint64_t*>(bytes)[0]})) {
+#endif
+
+BasicDecimal256& BasicDecimal256::Negate() {
+ uint64_t carry = 1;
+ for (uint64_t& elem : little_endian_array_) {
+ elem = ~elem + carry;
+ carry &= (elem == 0);
+ }
+ return *this;
+}
+
+BasicDecimal256& BasicDecimal256::Abs() { return *this < 0 ? Negate() : *this;
}
+
+BasicDecimal256 BasicDecimal256::Abs(const BasicDecimal256& in) {
+ BasicDecimal256 result(in);
+ return result.Abs();
+}
+
+std::array<uint8_t, 32> BasicDecimal256::ToBytes() const {
+ std::array<uint8_t, 32> out{{0}};
+ ToBytes(out.data());
+ return out;
+}
+
+void BasicDecimal256::ToBytes(uint8_t* out) const {
+ DCHECK_NE(out, nullptr);
+#if ARROW_LITTLE_ENDIAN
+ reinterpret_cast<int64_t*>(out)[0] = little_endian_array_[0];
+ reinterpret_cast<int64_t*>(out)[1] = little_endian_array_[1];
+ reinterpret_cast<int64_t*>(out)[2] = little_endian_array_[2];
+ reinterpret_cast<int64_t*>(out)[3] = little_endian_array_[3];
+#else
+ reinterpret_cast<int64_t*>(out)[0] = little_endian_array_[3];
+ reinterpret_cast<int64_t*>(out)[1] = little_endian_array_[2];
+ reinterpret_cast<int64_t*>(out)[2] = little_endian_array_[1];
+ reinterpret_cast<int64_t*>(out)[3] = little_endian_array_[0];
+#endif
+}
+
+BasicDecimal256& BasicDecimal256::operator*=(const BasicDecimal256& right) {
+ // Since the max value of BasicDecimal256 is supposed to be 1e76 - 1 and the
+ // min the negation taking the absolute values here should always be safe.
+ const bool negate = Sign() != right.Sign();
+ BasicDecimal256 x = BasicDecimal256::Abs(*this);
+ BasicDecimal256 y = BasicDecimal256::Abs(right);
+
+ uint128_t r_hi;
+ uint128_t r_lo;
+ std::array<uint64_t, 4> res{0, 0, 0, 0};
+ MultiplyUnsignedArray<4>(x.little_endian_array_, y.little_endian_array_,
&res);
+ little_endian_array_ = res;
+ if (negate) {
+ Negate();
+ }
+ return *this;
+}
+
+DecimalStatus BasicDecimal256::Rescale(int32_t original_scale, int32_t
new_scale,
+ BasicDecimal256* out) const {
+ if (original_scale == new_scale) {
+ return DecimalStatus::kSuccess;
+ }
+ // TODO: implement.
+ return DecimalStatus::kRescaleDataLoss;
+}
+
+BasicDecimal256 operator*(const BasicDecimal256& left, const BasicDecimal256&
right) {
+ BasicDecimal256 result = left;
+ result *= right;
+ return result;
+}
+
+bool operator==(const BasicDecimal256& left, const BasicDecimal256& right) {
+ return left.little_endian_array() == right.little_endian_array();
+}
+
+bool operator!=(const BasicDecimal256& left, const BasicDecimal256& right) {
+ return left.little_endian_array() != right.little_endian_array();
+}
+
+bool operator<(const BasicDecimal256& left, const BasicDecimal256& right) {
+ const std::array<uint64_t, 4>& lhs = left.little_endian_array();
+ const std::array<uint64_t, 4>& rhs = right.little_endian_array();
+ return lhs[3] != rhs[3]
+ ? static_cast<int64_t>(lhs[3]) < static_cast<int64_t>(rhs[3])
+ : lhs[2] != rhs[2] ? lhs[2] < rhs[2]
+ : lhs[1] != rhs[1] ? lhs[1] < rhs[1] : lhs[0]
< rhs[0];
+}
+
+bool operator<=(const BasicDecimal256& left, const BasicDecimal256& right) {
+ return !operator>(left, right);
Review comment:
Also, these indirections may be put in the `.h` as inline methods.
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