Move endianness check to compile time if it possible

fmtlib · Jan 4, 2022 · 3f6e0f1 · 3f6e0f1
1 parent 074cc78
commit 3f6e0f1
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Showing 2 changed files with 12 additions and 2 deletions.
diff --git a/include/fmt/chrono.h b/include/fmt/chrono.h
@@ -558,7 +558,7 @@ inline void write_digit2_separated(char* buf, unsigned a, unsigned b,
   auto usep = static_cast<unsigned long long>(sep);
   // Add ASCII '0' to each digit byte and insert separators.
   digits |= 0x3030003030003030 | (usep << 16) | (usep << 40);
-  if (is_big_endian()) {
+  if (const_check(is_big_endian())) {
     char tmp[8];
     memcpy(tmp, &digits, 8);
     std::reverse_copy(tmp, tmp + 8, buf);

diff --git a/include/fmt/format.h b/include/fmt/format.h
@@ -295,12 +295,22 @@ FMT_CONSTEXPR20 auto bit_cast(const From& from) -> To {
   return to;
 }
 
+#ifdef _WIN32
+constexpr auto is_big_endian() -> bool { return false; }
+#elif defined(__BIG_ENDIAN__)
+constexpr auto is_big_endian() -> bool { return true; }
+#elif defined(__BYTE_ORDER__) && defined(__ORDER_BIG_ENDIAN__)
+constexpr auto is_big_endian() -> bool {
+  return __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__;
+}
+#else
 inline auto is_big_endian() -> bool {
   struct bytes {
     char data[sizeof(int)];
   };
   return bit_cast<bytes>(1).data[0] == 0;
 }
+#endif
 
 // A fallback implementation of uintptr_t for systems that lack it.
 struct fallback_uintptr {
@@ -309,7 +319,7 @@ struct fallback_uintptr {
   fallback_uintptr() = default;
   explicit fallback_uintptr(const void* p) {
     *this = bit_cast<fallback_uintptr>(p);
-    if (is_big_endian()) {
+    if (const_check(is_big_endian())) {
       for (size_t i = 0, j = sizeof(void*) - 1; i < j; ++i, --j)
         std::swap(value[i], value[j]);
     }