Auto-detect bswap operations

source/m3_config_platforms.h

@@ -191,6 +191,18 @@
  * Detect/define features
  */
 
+# ifdef __has_feature
+#  define M3_COMPILER_HAS_FEATURE(x) __has_feature(x)
+# else
+#  define M3_COMPILER_HAS_FEATURE(x) 0
+# endif
+
+# ifdef __has_builtin
+#  define M3_COMPILER_HAS_BUILTIN(x) __has_builtin(x)
+# else
+#  define M3_COMPILER_HAS_BUILTIN(x) 0
+# endif
+
 # if defined(M3_COMPILER_MSVC)
 #  include <stdint.h>
 #  if UINTPTR_MAX == 0xFFFFFFFF
@@ -218,11 +230,57 @@
 
 // Byte swapping (for Big-Endian systems only)
 
+# if defined(_MSC_VER)
+#  define m3_bswap16(x)     _byteswap_ushort((x))
+#  define m3_bswap32(x)     _byteswap_ulong((x))
+#  define m3_bswap64(x)     _byteswap_uint64((x))
+# elif defined(__GNUC__) && __GNUC_PREREQ(4, 8)
+// __builtin_bswap32/64 added in gcc 4.3, __builtin_bswap16 added in gcc 4.8
+#  define m3_bswap16(x)     __builtin_bswap16((x))
+#  define m3_bswap32(x)     __builtin_bswap32((x))
+#  define m3_bswap64(x)     __builtin_bswap64((x))
+# elif M3_COMPILER_HAS_BUILTIN(__builtin_bswap16)
+#  define m3_bswap16(x)     __builtin_bswap16((x))
+#  define m3_bswap32(x)     __builtin_bswap32((x))
+#  define m3_bswap64(x)     __builtin_bswap64((x))
+# else
+#  include <endian.h>
+#  if defined(__bswap_16)
+#   define m3_bswap16(x)     __bswap_16((x))
+#   define m3_bswap32(x)     __bswap_32((x))
+#   define m3_bswap64(x)     __bswap_64((x))
+#  else
+#   warning "Using naive (probably slow) bswap operations"
+    static inline
+    uint16_t m3_bswap16(uint16_t x) {
+      return ((( x  >> 8 ) & 0xffu ) | (( x  & 0xffu ) << 8 ));
+    }
+    static inline
+    uint32_t m3_bswap32(uint32_t x) {
+      return ((( x & 0xff000000u ) >> 24 ) |
+              (( x & 0x00ff0000u ) >> 8  ) |
+              (( x & 0x0000ff00u ) << 8  ) |
+              (( x & 0x000000ffu ) << 24 ));
+    }
+    static inline
+    uint64_t m3_bswap64(uint64_t x) {
+      return ((( x & 0xff00000000000000ull ) >> 56 ) |
+              (( x & 0x00ff000000000000ull ) >> 40 ) |
+              (( x & 0x0000ff0000000000ull ) >> 24 ) |
+              (( x & 0x000000ff00000000ull ) >> 8  ) |
+              (( x & 0x00000000ff000000ull ) << 8  ) |
+              (( x & 0x0000000000ff0000ull ) << 24 ) |
+              (( x & 0x000000000000ff00ull ) << 40 ) |
+              (( x & 0x00000000000000ffull ) << 56 ));
+    }
+#  endif
+# endif
+
 # if defined(M3_BIG_ENDIAN)
 #  define M3_BSWAP_u8(X)  {}
-#  define M3_BSWAP_u16(X) { (X)=__builtin_bswap16((X)); }
-#  define M3_BSWAP_u32(X) { (X)=__builtin_bswap32((X)); }
-#  define M3_BSWAP_u64(X) { (X)=__builtin_bswap64((X)); }
+#  define M3_BSWAP_u16(X) { (X)=m3_bswap16((X)); }
+#  define M3_BSWAP_u32(X) { (X)=m3_bswap32((X)); }
+#  define M3_BSWAP_u64(X) { (X)=m3_bswap64((X)); }
 #  define M3_BSWAP_i8(X)  {}
 #  define M3_BSWAP_i16(X) M3_BSWAP_u16(X)
 #  define M3_BSWAP_i32(X) M3_BSWAP_u32(X)