diff --git a/libcxx/include/__charconv/to_chars_base_10.h b/libcxx/include/__charconv/to_chars_base_10.h
--- a/libcxx/include/__charconv/to_chars_base_10.h
+++ b/libcxx/include/__charconv/to_chars_base_10.h
@@ -10,10 +10,10 @@
 #ifndef _LIBCPP___CHARCONV_TO_CHARS_BASE_10_H
 #define _LIBCPP___CHARCONV_TO_CHARS_BASE_10_H
 
+#include <__algorithm/copy_n.h>
 #include <__charconv/tables.h>
 #include <__config>
 #include <cstdint>
-#include <cstring>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
@@ -25,98 +25,97 @@
 
 namespace __itoa {
 
-template <class _Tp>
-_LIBCPP_HIDE_FROM_ABI char* __append1(char* __buffer, _Tp __value) noexcept {
-  *__buffer = '0' + static_cast<char>(__value);
-  return __buffer + 1;
+_LIBCPP_HIDE_FROM_ABI inline char* __append1(char* __first, uint32_t __value) noexcept {
+  *__first = '0' + static_cast<char>(__value);
+  return __first + 1;
 }
 
-template <class _Tp>
-_LIBCPP_HIDE_FROM_ABI char* __append2(char* __buffer, _Tp __value) noexcept {
-  std::memcpy(__buffer, &__table<>::__digits_base_10[(__value)*2], 2);
-  return __buffer + 2;
+_LIBCPP_HIDE_FROM_ABI inline char* __append2(char* __first, uint32_t __value) noexcept {
+  return std::copy_n(&__table<>::__digits_base_10[__value * 2], 2, __first);
 }
 
-template <class _Tp>
-_LIBCPP_HIDE_FROM_ABI char* __append3(char* __buffer, _Tp __value) noexcept {
-  return __itoa::__append2(__itoa::__append1(__buffer, (__value) / 100), (__value) % 100);
+_LIBCPP_HIDE_FROM_ABI inline char* __append3(char* __first, uint32_t __value) noexcept {
+  return __itoa::__append2(__itoa::__append1(__first, __value / 100), __value % 100);
 }
 
-template <class _Tp>
-_LIBCPP_HIDE_FROM_ABI char* __append4(char* __buffer, _Tp __value) noexcept {
-  return __itoa::__append2(__itoa::__append2(__buffer, (__value) / 100), (__value) % 100);
+_LIBCPP_HIDE_FROM_ABI inline char* __append4(char* __first, uint32_t __value) noexcept {
+  return __itoa::__append2(__itoa::__append2(__first, __value / 100), __value % 100);
 }
 
-template <class _Tp>
-_LIBCPP_HIDE_FROM_ABI char* __append2_no_zeros(char* __buffer, _Tp __value) noexcept {
-  if (__value < 10)
-    return __itoa::__append1(__buffer, __value);
-  else
-    return __itoa::__append2(__buffer, __value);
+_LIBCPP_HIDE_FROM_ABI inline char* __append5(char* __first, uint32_t __value) noexcept {
+  return __itoa::__append4(__itoa::__append1(__first, __value / 10000), __value % 10000);
 }
 
-template <class _Tp>
-_LIBCPP_HIDE_FROM_ABI char* __append4_no_zeros(char* __buffer, _Tp __value) noexcept {
-  if (__value < 100)
-    return __itoa::__append2_no_zeros(__buffer, __value);
-  else if (__value < 1000)
-    return __itoa::__append3(__buffer, __value);
-  else
-    return __itoa::__append4(__buffer, __value);
+_LIBCPP_HIDE_FROM_ABI inline char* __append6(char* __first, uint32_t __value) noexcept {
+  return __itoa::__append4(__itoa::__append2(__first, __value / 10000), __value % 10000);
+}
+
+_LIBCPP_HIDE_FROM_ABI inline char* __append7(char* __first, uint32_t __value) noexcept {
+  return __itoa::__append6(__itoa::__append1(__first, __value / 1000000), __value % 1000000);
 }
 
+_LIBCPP_HIDE_FROM_ABI inline char* __append8(char* __first, uint32_t __value) noexcept {
+  return __itoa::__append6(__itoa::__append2(__first, __value / 1000000), __value % 1000000);
+}
+
+_LIBCPP_HIDE_FROM_ABI inline char* __append9(char* __first, uint32_t __value) noexcept {
+  return __itoa::__append8(__itoa::__append1(__first, __value / 100000000), __value % 100000000);
+}
+
+// This function is used for uint32_t and uint64_t.
 template <class _Tp>
-_LIBCPP_HIDE_FROM_ABI char* __append8_no_zeros(char* __buffer, _Tp __value) noexcept {
-  if (__value < 10000)
-    __buffer = __itoa::__append4_no_zeros(__buffer, __value);
-  else {
-    __buffer = __itoa::__append4_no_zeros(__buffer, __value / 10000);
-    __buffer = __itoa::__append4(__buffer, __value % 10000);
-  }
-  return __buffer;
+_LIBCPP_HIDE_FROM_ABI char* __append10(char* __first, _Tp __value) noexcept {
+  return __itoa::__append8(__itoa::__append2(__first, static_cast<uint32_t>(__value / 100000000)),
+                           static_cast<uint32_t>(__value % 100000000));
 }
 
-_LIBCPP_HIDE_FROM_ABI inline char* __base_10_u32(uint32_t __value, char* __buffer) noexcept {
-  if (__value < 100000000)
-    __buffer = __itoa::__append8_no_zeros(__buffer, __value);
-  else {
-    // __value = aabbbbcccc in decimal
-    const uint32_t __a = __value / 100000000; // 1 to 42
-    __value %= 100000000;
-
-    __buffer = __itoa::__append2_no_zeros(__buffer, __a);
-    __buffer = __itoa::__append4(__buffer, __value / 10000);
-    __buffer = __itoa::__append4(__buffer, __value % 10000);
+_LIBCPP_HIDE_FROM_ABI inline char* __base_10_u32(char* __first, uint32_t __value) noexcept {
+  if (__value < 1000000) {
+    if (__value < 10000) {
+      if (__value < 100) {
+        // 0 <= __value < 100
+        if (__value < 10)
+          return __itoa::__append1(__first, __value);
+        return __itoa::__append2(__first, __value);
+      }
+      // 100 <= __value < 10'000
+      if (__value < 1000)
+        return __itoa::__append3(__first, __value);
+      return __itoa::__append4(__first, __value);
+    }
+
+    // 10'000 <= __value < 1'000'000
+    if (__value < 100000)
+      return __itoa::__append5(__first, __value);
+    return __itoa::__append6(__first, __value);
   }
 
-  return __buffer;
+  // __value => 1'000'000
+  if (__value < 100000000) {
+    // 1'000'000 <= __value < 100'000'000
+    if (__value < 10000000)
+      return __itoa::__append7(__first, __value);
+    return __itoa::__append8(__first, __value);
+  }
+
+  // 100'000'000 <= __value < max
+  if (__value < 1000000000)
+    return __itoa::__append9(__first, __value);
+  return __itoa::__append10(__first, __value);
 }
 
-_LIBCPP_HIDE_FROM_ABI inline char* __base_10_u64(uint64_t __value, char* __buffer) noexcept {
-  if (__value < 100000000)
-    __buffer = __itoa::__append8_no_zeros(__buffer, static_cast<uint32_t>(__value));
-  else if (__value < 10000000000000000) {
-    const uint32_t __v0 = static_cast<uint32_t>(__value / 100000000);
-    const uint32_t __v1 = static_cast<uint32_t>(__value % 100000000);
-
-    __buffer = __itoa::__append8_no_zeros(__buffer, __v0);
-    __buffer = __itoa::__append4(__buffer, __v1 / 10000);
-    __buffer = __itoa::__append4(__buffer, __v1 % 10000);
-  } else {
-    const uint32_t __a = static_cast<uint32_t>(__value / 10000000000000000); // 1 to 1844
-    __value %= 10000000000000000;
-
-    __buffer = __itoa::__append4_no_zeros(__buffer, __a);
-
-    const uint32_t __v0 = static_cast<uint32_t>(__value / 100000000);
-    const uint32_t __v1 = static_cast<uint32_t>(__value % 100000000);
-    __buffer = __itoa::__append4(__buffer, __v0 / 10000);
-    __buffer = __itoa::__append4(__buffer, __v0 % 10000);
-    __buffer = __itoa::__append4(__buffer, __v1 / 10000);
-    __buffer = __itoa::__append4(__buffer, __v1 % 10000);
-  }
+_LIBCPP_HIDE_FROM_ABI inline char* __base_10_u64(char* __buffer, uint64_t __value) noexcept {
+  if (__value <= UINT32_MAX)
+    return __itoa::__base_10_u32(__buffer, static_cast<uint32_t>(__value));
 
-  return __buffer;
+  // Numbers in the range UINT32_MAX <= val < 10'000'000'000 always contain 10
+  // digits and are outputted after this if statement.
+  if (__value >= 10000000000) {
+    // This function properly deterimines the first non-zero leading digit.
+    __buffer = __itoa::__base_10_u32(__buffer, static_cast<uint32_t>(__value / 10000000000));
+    __value %= 10000000000;
+  }
+  return __itoa::__append10(__buffer, __value);
 }
 
 } // namespace __itoa
diff --git a/libcxx/include/charconv b/libcxx/include/charconv
--- a/libcxx/include/charconv
+++ b/libcxx/include/charconv
@@ -125,9 +125,9 @@
         return __t - (__v < __table<>::__pow10_64[__t]) + 1;
     }
 
-    static _LIBCPP_HIDE_FROM_ABI char* __convert(_Tp __v, char* __p)
+    static _LIBCPP_HIDE_FROM_ABI char* __convert(char* __p, _Tp __v)
     {
-        return __itoa::__base_10_u64(__v, __p);
+        return __itoa::__base_10_u64(__p, __v);
     }
 
     static _LIBCPP_HIDE_FROM_ABI decltype(__table<>::__pow10_64)& __pow() { return __table<>::__pow10_64; }
@@ -145,9 +145,9 @@
         return __t - (__v < __table<>::__pow10_32[__t]) + 1;
     }
 
-    static _LIBCPP_HIDE_FROM_ABI char* __convert(_Tp __v, char* __p)
+    static _LIBCPP_HIDE_FROM_ABI char* __convert(char* __p, _Tp __v)
     {
-        return __itoa::__base_10_u32(__v, __p);
+        return __itoa::__base_10_u32(__p, __v);
     }
 
     static _LIBCPP_HIDE_FROM_ABI decltype(__table<>::__pow10_32)& __pow() { return __table<>::__pow10_32; }
@@ -262,7 +262,7 @@
     auto __diff = __last - __first;
 
     if (__tx::digits <= __diff || __tx::__width(__value) <= __diff)
-        return {__tx::__convert(__value, __first), errc(0)};
+        return {__tx::__convert(__first, __value), errc(0)};
     else
         return {__last, errc::value_too_large};
 }
diff --git a/libcxx/src/charconv.cpp b/libcxx/src/charconv.cpp
--- a/libcxx/src/charconv.cpp
+++ b/libcxx/src/charconv.cpp
@@ -21,13 +21,13 @@
 _LIBCPP_FUNC_VIS char*
 __u32toa(uint32_t value, char* buffer) noexcept
 {
-	return __base_10_u32(value, buffer);
+	return __base_10_u32(buffer, value);
 }
 
 _LIBCPP_FUNC_VIS char*
 __u64toa(uint64_t value, char* buffer) noexcept
 {
-	return __base_10_u64(value, buffer);
+	return __base_10_u64(buffer, value);
 }
 
 }  // namespace __itoa