Improve endian check if macro is not set

Author: oschwald

Changes.md

@@ -2,6 +2,7 @@
 
 * The handling of float and double types was rewritten to fix compiler errors
   and to eliminate the use of volatile.
+* Improved endian preprocessor check if `MMDB_LITTLE_ENDIAN` is not set.
 
 ## 1.12.2 - 2025-01-10
 

include/maxminddb.h

@@ -12,6 +12,14 @@ extern "C" {
 #include <stdio.h>
 #include <sys/types.h>
 
+#ifdef __has_include
+#if __has_include(<endian.h>)
+#include <endian.h>
+#elif __has_include(<sys/endian.h>)
+#include <sys/endian.h>
+#endif
+#endif
+
 #ifdef _WIN32
 #include <winsock2.h>
 #include <ws2tcpip.h>
@@ -28,6 +36,17 @@ extern "C" {
 #include <sys/socket.h>
 #endif
 
+#if !defined(MMDB_LITTLE_ENDIAN)
+#if defined(__BYTE_ORDER__) && defined(__ORDER_LITTLE_ENDIAN__)
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+#define MMDB_LITTLE_ENDIAN 1
+#endif
+#elif defined(_WIN32) || defined(_WIN64)
+// We assume modern Windows targets are little endian
+#define MMDB_LITTLE_ENDIAN 1
+#endif
+#endif
+
 #define MMDB_DATA_TYPE_EXTENDED (0)
 #define MMDB_DATA_TYPE_POINTER (1)
 #define MMDB_DATA_TYPE_UTF8_STRING (2)

src/maxminddb.c

@@ -1803,9 +1803,7 @@ static float get_ieee754_float(const uint8_t *restrict p) {
 
     memcpy(&i, p, sizeof(uint32_t));
 
-/* Windows builds don't use autoconf but we can assume they're all
- * little-endian. */
-#if MMDB_LITTLE_ENDIAN || _WIN32
+#if MMDB_LITTLE_ENDIAN
     i = bswap32(i);
 #endif
 
@@ -1820,7 +1818,7 @@ static double get_ieee754_double(const uint8_t *restrict p) {
 
     memcpy(&i, p, sizeof(uint64_t));
 
-#if MMDB_LITTLE_ENDIAN || _WIN32
+#if MMDB_LITTLE_ENDIAN
     i = bswap64(i);
 #endif