should be it

external/duckdb/extension/parquet/include/parquet_decimal_utils.hpp

@@ -0,0 +1,55 @@
+//===----------------------------------------------------------------------===//
+//                         DuckDB
+//
+// parquet_decimal_utils.hpp
+//
+//
+//===----------------------------------------------------------------------===//
+
+#pragma once
+
+#include "column_reader.hpp"
+#include "reader/templated_column_reader.hpp"
+
+namespace duckdb {
+
+class ParquetDecimalUtils {
+public:
+	template <class PHYSICAL_TYPE>
+	static PHYSICAL_TYPE ReadDecimalValue(const_data_ptr_t pointer, idx_t size, const ParquetColumnSchema &) {
+		PHYSICAL_TYPE res = 0;
+
+		auto res_ptr = (uint8_t *)&res;
+		bool positive = (*pointer & 0x80) == 0;
+
+		// numbers are stored as two's complement so some muckery is required
+		for (idx_t i = 0; i < MinValue<idx_t>(size, sizeof(PHYSICAL_TYPE)); i++) {
+			auto byte = *(pointer + (size - i - 1));
+			res_ptr[i] = positive ? byte : byte ^ 0xFF;
+		}
+		// Verify that there are only 0s here
+		if (size > sizeof(PHYSICAL_TYPE)) {
+			for (idx_t i = sizeof(PHYSICAL_TYPE); i < size; i++) {
+				auto byte = *(pointer + (size - i - 1));
+				if (!positive) {
+					byte ^= 0xFF;
+				}
+				if (byte != 0) {
+					throw InvalidInputException("Invalid decimal encoding in Parquet file");
+				}
+			}
+		}
+		if (!positive) {
+			res += 1;
+			return -res;
+		}
+		return res;
+	}
+
+	static unique_ptr<ColumnReader> CreateReader(ParquetReader &reader, const ParquetColumnSchema &schema);
+};
+
+template <>
+double ParquetDecimalUtils::ReadDecimalValue(const_data_ptr_t pointer, idx_t size, const ParquetColumnSchema &schema);
+
+} // namespace duckdb