From c9eef4572efd3d660b7b00e835fe8f1e35c08036 Mon Sep 17 00:00:00 2001
From: Roman Koshelev <roman.koshelev@bk.ru>
Date: Tue, 31 Aug 2021 07:51:06 +0300
Subject: [PATCH] Fix copy_str performance

---
 include/fmt/core.h | 25 +++++++++++++++++++------
 1 file changed, 19 insertions(+), 6 deletions(-)

diff --git a/include/fmt/core.h b/include/fmt/core.h
index 2f0cfb0b72c55..afb0075980eeb 100644
--- a/include/fmt/core.h
+++ b/include/fmt/core.h
@@ -740,19 +740,32 @@ inline auto get_container(std::back_insert_iterator<Container> it)
 }
 
 template <typename Char, typename InputIt, typename OutputIt>
-FMT_CONSTEXPR auto copy_str(InputIt begin, InputIt end, OutputIt out)
+FMT_CONSTEXPR auto copy_str_constexpr(InputIt begin, InputIt end, OutputIt out)
     -> OutputIt {
   while (begin != end) *out++ = static_cast<Char>(*begin++);
   return out;
 }
 
-template <typename Char, FMT_ENABLE_IF(std::is_same<Char, char>::value)>
-FMT_CONSTEXPR auto copy_str(const Char* begin, const Char* end, Char* out)
-    -> Char* {
+template <typename Char, typename InputIt, typename OutputIt>
+FMT_CONSTEXPR auto copy_str(InputIt begin, InputIt end, OutputIt out)
+    -> OutputIt {
+  return copy_str_constexpr<Char>(begin, end, out);
+}
+
+template <typename Char, typename InputIt, typename OutputIt>
+FMT_CONSTEXPR
+typename std::enable_if
+<
+  std::is_same<typename std::remove_const<InputIt>::type, OutputIt>::value &&
+  std::is_trivially_copy_assignable<OutputIt>::value,
+  OutputIt*
+>::type
+copy_str(InputIt* begin, InputIt* end, OutputIt* out)
+{
   if (is_constant_evaluated())
-    return copy_str<Char, const Char*, Char*>(begin, end, out);
+    return copy_str_constexpr<Char>(begin, end, out);
   auto size = to_unsigned(end - begin);
-  memcpy(out, begin, size);
+  memcpy(out, begin, size * sizeof(OutputIt));
   return out + size;
 }