diff --git a/libc/src/__support/builtin_wrappers.h b/libc/src/__support/builtin_wrappers.h
--- a/libc/src/__support/builtin_wrappers.h
+++ b/libc/src/__support/builtin_wrappers.h
@@ -64,6 +64,58 @@
   return __internal::clz(val);
 }
 
+// Add with carry
+template <typename T>
+inline constexpr T add_with_carry(T a, T b, T carry_in, T &carry_out) {
+  T tmp = a + carry_in;
+  T sum = b + tmp;
+  carry_out = (sum < b) | (tmp < a);
+  return sum;
+}
+
+#if __has_builtin(__builtin_addc)
+// https://clang.llvm.org/docs/LanguageExtensions.html#multiprecision-arithmetic-builtins
+
+template <>
+inline unsigned char add_with_carry<unsigned char>(unsigned char a,
+                                                   unsigned char b,
+                                                   unsigned char carry_in,
+                                                   unsigned char &carry_out) {
+  return __builtin_addcb(a, b, carry_in, &carry_out);
+}
+
+template <>
+inline unsigned short
+add_with_carry<unsigned short>(unsigned short a, unsigned short b,
+                               unsigned short carry_in,
+                               unsigned short &carry_out) {
+  return __builtin_addcs(a, b, carry_in, &carry_out);
+}
+
+template <>
+inline unsigned int add_with_carry<unsigned int>(unsigned int a, unsigned int b,
+                                                 unsigned int carry_in,
+                                                 unsigned int &carry_out) {
+  return __builtin_addc(a, b, carry_in, &carry_out);
+}
+
+template <>
+inline unsigned long add_with_carry<unsigned long>(unsigned long a,
+                                                   unsigned long b,
+                                                   unsigned long carry_in,
+                                                   unsigned long &carry_out) {
+  return __builtin_addcl(a, b, carry_in, &carry_out);
+}
+
+template <>
+inline unsigned long long
+add_with_carry<unsigned long long>(unsigned long long a, unsigned long long b,
+                                   unsigned long long carry_in,
+                                   unsigned long long &carry_out) {
+  return __builtin_addcll(a, b, carry_in, &carry_out);
+}
+#endif // __has_builtin(__builtin_addc)
+
 } // namespace __llvm_libc
 
 #endif // LLVM_LIBC_SRC_SUPPORT_BUILTIN_WRAPPERS_H