Support new FST writer API (#6871) (#6992)

include/fstcpp/fstcpp_variable_info.cpp

@@ -0,0 +1,39 @@
+// SPDX-FileCopyrightText: 2026 Yu-Sheng Lin <[email protected]>
+// SPDX-License-Identifier: MIT
+// Project: libfstwriter
+// Website: https://github.com/gtkwave/libfstwriter
+// direct include
+#include "fstcpp/fstcpp_variable_info.h"
+// C system headers
+// C++ standard library headers
+#include <algorithm>
+// Other libraries' .h files.
+// Your project's .h files.
+
+namespace fst {
+
+// I don't know why I need to define them here, but StackOverflow says it
+constexpr uint64_t VariableInfo::kCapacityBaseShift;
+constexpr uint64_t VariableInfo::kCapacityBase;
+
+void VariableInfo::reallocate(uint64_t new_size) {
+	// Allocate new memory
+	const uint32_t new_capacity_log2{
+		std::max(
+			static_cast<uint32_t>(platform::clog2(new_size)),
+			static_cast<uint32_t>(kCapacityBaseShift)
+		) -
+		static_cast<uint32_t>(kCapacityBaseShift)
+	};
+	uint8_t *new_data{new uint8_t[kCapacityBase << new_capacity_log2]};
+	// Copy old data to new memory
+	if (m_data != nullptr) {
+		const uint64_t old_size{size()};
+		std::copy_n(m_data, old_size, new_data);
+		delete[] m_data;
+	}
+	m_data = new_data;
+	capacity_log2(new_capacity_log2);
+}
+
+}  // namespace fst