diff --git a/iguana/pb_util.hpp b/iguana/pb_util.hpp
new file mode 100644
index 00000000..37f34a77
--- /dev/null
+++ b/iguana/pb_util.hpp
@@ -0,0 +1,92 @@
+#pragma once
+#include <cassert>
+#include <cstring>
+#include <map>
+#include <string>
+#include <vector>
+
+namespace iguana {
+namespace detail {
+[[nodiscard]] inline uint32_t encode_zigzag(int32_t v) {
+  return (static_cast<uint32_t>(v) << 1U) ^
+         static_cast<uint32_t>(
+             -static_cast<int32_t>(static_cast<uint32_t>(v) >> 31U));
+}
+[[nodiscard]] inline uint64_t encode_zigzag(int64_t v) {
+  return (static_cast<uint64_t>(v) << 1U) ^
+         static_cast<uint64_t>(
+             -static_cast<int64_t>(static_cast<uint64_t>(v) >> 63U));
+}
+
+[[nodiscard]] inline int64_t decode_zigzag(uint64_t u) {
+  return static_cast<int64_t>((u >> 1U)) ^
+         static_cast<uint64_t>(-static_cast<int64_t>(u & 1U));
+}
+[[nodiscard]] inline int64_t decode_zigzag(uint32_t u) {
+  return static_cast<int64_t>((u >> 1U)) ^
+         static_cast<uint64_t>(-static_cast<int64_t>(u & 1U));
+}
+
+[[nodiscard]] inline bool decode_varint(const char* data, std::size_t& pos_,
+                                        std::size_t size_, uint64_t& v) {
+  // fix test failed on arm due to different char definition
+  const signed char* data_ = reinterpret_cast<const signed char*>(data);
+  // from https://github.com/facebook/folly/blob/main/folly/Varint.h
+  if (pos_ < size_ && (static_cast<uint64_t>(data_[pos_]) & 0x80U) == 0) {
+    v = static_cast<uint64_t>(data_[pos_]);
+    pos_++;
+    return true;
+  }
+  constexpr const int8_t max_varint_length = sizeof(uint64_t) * 8 / 7 + 1;
+  uint64_t val = 0;
+  if (size_ - pos_ >= max_varint_length) [[likely]] {
+    do {
+      // clang-format off
+                int64_t b = data_[pos_++];
+                val  = ((uint64_t(b) & 0x7fU)       ); if (b >= 0) { break; }
+                b = data_[pos_++]; val |= ((uint64_t(b) & 0x7fU) <<  7U); if (b >= 0) { break; }
+                b = data_[pos_++]; val |= ((uint64_t(b) & 0x7fU) << 14U); if (b >= 0) { break; }
+                b = data_[pos_++]; val |= ((uint64_t(b) & 0x7fU) << 21U); if (b >= 0) { break; }
+                b = data_[pos_++]; val |= ((uint64_t(b) & 0x7fU) << 28U); if (b >= 0) { break; }
+                b = data_[pos_++]; val |= ((uint64_t(b) & 0x7fU) << 35U); if (b >= 0) { break; }
+                b = data_[pos_++]; val |= ((uint64_t(b) & 0x7fU) << 42U); if (b >= 0) { break; }
+                b = data_[pos_++]; val |= ((uint64_t(b) & 0x7fU) << 49U); if (b >= 0) { break; }
+                b = data_[pos_++]; val |= ((uint64_t(b) & 0x7fU) << 56U); if (b >= 0) { break; }
+                b = data_[pos_++]; val |= ((uint64_t(b) & 0x01U) << 63U); if (b >= 0) { break; }
+      // clang-format on
+      return false;
+    } while (false);
+  }
+  else {
+    unsigned int shift = 0;
+    while (pos_ != size_ && int64_t(data_[pos_]) < 0) {
+      val |= (uint64_t(data_[pos_++]) & 0x7fU) << shift;
+      shift += 7;
+    }
+    if (pos_ == size_) {
+      return false;
+    }
+    val |= uint64_t(data_[pos_++]) << shift;
+  }
+  v = val;
+  return true;
+}
+
+template <typename Stream>
+inline void serialize_varint(uint64_t v, Stream& out) {
+  while (v >= 0x80) {
+    out.push_back(static_cast<uint8_t>(v | 0x80));
+    v >>= 7;
+  }
+  out.push_back(static_cast<uint8_t>(v));
+}
+[[nodiscard]] inline bool deserialize_varint(const char* data, std::size_t& pos,
+                                             std::size_t size, uint64_t& v) {
+  return decode_varint(data, pos, size, v);
+}
+[[nodiscard]] inline bool read_tag(const char* data, std::size_t& pos,
+                                   std::size_t size, uint64_t& tag) {
+  return deserialize_varint(data, pos, size, tag);
+}
+}  // namespace detail
+}  // namespace iguana
\ No newline at end of file
diff --git a/iguana/struct_pb.hpp b/iguana/struct_pb.hpp
index f10edc0b..9ad5c4dd 100644
--- a/iguana/struct_pb.hpp
+++ b/iguana/struct_pb.hpp
@@ -7,7 +7,9 @@
 #include <utility>
 #include <variant>
 
+#include "pb_util.hpp"
 #include "reflection.hpp"
+
 namespace iguana {
 namespace detail {
 enum class WireType : uint32_t {
@@ -19,53 +21,21 @@ enum class WireType : uint32_t {
   Fixed32 = 5,
 };
 
-template <class To, class From>
-inline To bit_cast(From from) {
-  static_assert(sizeof(To) == sizeof(From), "");
-  static_assert(std::is_trivially_copyable_v<To>, "");
-  static_assert(std::is_trivially_copyable_v<From>, "");
-
-  To to;
-  std::memcpy(&to, &from, sizeof(from));
-  return to;
-}
-
-inline void write_varint(uint32_t value, auto& out) {
-  uint8_t b[5]{};
-  for (size_t i = 0; i < 5; ++i) {
-    b[i] = value & 0b0111'1111;
-    value >>= 7;
-    if (value) {
-      b[i] |= 0b1000'0000;
-    }
-    else {
-      out.append((const char*)b, i + 1);
-      // out.write(b, i + 1);
-      break;
-    }
-  }
-}
-
-inline void write_varint(int32_t value, auto& out) {
-  write_varint(bit_cast<uint32_t>(value), out);
-}
-
 inline uint32_t make_tag_wire_type(uint32_t tag, WireType wire_type) {
   return (tag << 3) | static_cast<uint32_t>(wire_type);
 }
 
-inline void write_tag_wire_type(uint32_t tag, WireType wire_type, auto& out) {
-  write_varint(make_tag_wire_type(tag, wire_type), out);
-}
-
 struct varint_serializer {
-  static void serialize(uint32_t tag, int32_t value, auto& out) {
+  template <typename T>
+  static void serialize(uint32_t field_number, int32_t value, T& out) {
     if (value == 0) {
       return;
     }
 
-    write_tag_wire_type(tag, WireType::Varint, out);
-    write_varint(value, out);
+    uint32_t key =
+        (field_number << 3) | static_cast<uint32_t>(WireType::Varint);
+    serialize_varint(key, out);
+    serialize_varint(value, out);
   }
 };
 }  // namespace detail