fix: crc32 should not have byte order be platform dependent

Author: finger563

include/alpaca/detail/crc32.h

@@ -28,11 +28,10 @@
 // size_t
 #include <cstddef>
 
-// define endianess and some integer data types
-#if defined(_MSC_VER) || defined(__MINGW32__)
-// Windows always little endian
 #define __ALPACA_BYTE_ORDER __ALPACA_LITTLE_ENDIAN
 
+// define some integer data types
+#if defined(_MSC_VER) || defined(__MINGW32__)
 // intrinsics / prefetching
 #if defined(__MINGW32__) || defined(__clang__)
 #define ALPACA_PREFETCH(location) __builtin_prefetch(location)
@@ -42,41 +41,30 @@
 #define ALPACA_PREFETCH(location) _mm_prefetch(location, _MM_HINT_T0)
 #else
 #define ALPACA_PREFETCH(location) ;
-#endif
-#endif
+#endif // __SSE2__
+#endif // __MINGW32__
 #elif defined(__APPLE__) || defined(__MACH__)
-// Apple MacOS uses big endian
-#define __ALPACA_BYTE_ORDER __ALPACA_BIG_ENDIAN
-
 // intrinsics / prefetching
 #ifdef __GNUC__
 #define ALPACA_PREFETCH(location) __builtin_prefetch(location)
-#else
+#else // __GNUC__
 // no prefetching
 #define ALPACA_PREFETCH(location) ;
-#endif
+#endif // __GNUC__
 
 #elif defined(__linux__) || defined(__linux) || defined(linux__) ||            \
     defined(__gnu_linux__)
-// defines BYTE_ORDER as __ALPACA_LITTLE_ENDIAN or __ALPACA_BIG_ENDIAN
 #include <sys/param.h>
-#define __ALPACA_BYTE_ORDER __BYTE_ORDER
-
 // intrinsics / prefetching
 #ifdef __GNUC__
 #define ALPACA_PREFETCH(location) __builtin_prefetch(location)
-#else
+#else // __GNUC__
 // no prefetching
 #define ALPACA_PREFETCH(location) ;
-#endif
-#else
+#endif // __GNUC__
+#else // unknown system
 #error unsupported system
-#endif
-
-// abort if byte order is undefined
-#if !defined(__ALPACA_BYTE_ORDER)
-#error undefined byte order, compile with -D__ALPACA_BYTE_ORDER=1234 (if little endian) or -D__ALPACA_BYTE_ORDER=4321 (big endian)
-#endif
+#endif // system
 
 namespace {
 /// zlib's CRC32 polynomial
@@ -1386,4 +1374,4 @@ static inline uint32_t crc32_combine(uint32_t crcA, uint32_t crcB,
 
   // return combined crc
   return crcA ^ crcB;
-}
+}