Prevent unaligned memory access in adlib

This removes the last warnings in this area; in this case changing endianess
is not used for accessing emulated memory, just to flip few values to
low endian for storage.

INSTALL

@@ -50,7 +50,7 @@ alsa-lib (optional)
 
 If you want compile from developer sources (SVN) under a unix system, you will need:
  - Subversion to checkout the sources, or gzip and tar to unpack them from archive
- - GCC (>=4.8.1) or Clang (>=3.3)
+ - GCC (>=4.8.1) or Clang (>=3.4)
  - automake (>=1.6)
  - autoconf (>=2.50)
  - autoconf-archive (>=2009.x)

include/mem.h

@@ -105,6 +105,36 @@ static INLINE void host_writed(HostPt off,Bit32u val) {
 
 #endif
 
+// host_to_le functions allow for byte order conversion on big endian
+// architectures while respecting memory alignment on low endian.
+//
+// It is extremely unlikely that we'll ever try to compile on big endian arch
+// with a compiler missing __builtin_bswap*, so let's not overcomplicate
+// things.
+//
+// __builtin_bswap* is supported since GCC 4.3 and Clang 3.4
+
+#if defined(WORDS_BIGENDIAN)
+
+constexpr static INLINE uint16_t host_to_le(uint16_t val) {
+	return __builtin_bswap16(val);
+}
+
+constexpr static INLINE uint32_t host_to_le(uint32_t val) {
+	return __builtin_bswap32(val);
+}
+
+#else
+
+constexpr static INLINE uint16_t host_to_le(uint16_t val) {
+	return val;
+}
+
+constexpr static INLINE uint32_t host_to_le(uint32_t val) {
+	return val;
+}
+
+#endif
 
 static INLINE void var_write(Bit8u * var, Bit8u val) {
 	host_writeb(var, val);

src/hardware/adlib.cpp

@@ -328,10 +328,10 @@ class Capture {
 		if ( handle ) {
 			ClearBuf();
 			/* Endianize the header and write it to beginning of the file */
-			var_write( &header.versionHigh, header.versionHigh );
-			var_write( &header.versionLow, header.versionLow );
-			var_write( &header.commands, header.commands );
-			var_write( &header.milliseconds, header.milliseconds );
+			header.versionHigh  = host_to_le(header.versionHigh);
+			header.versionLow   = host_to_le(header.versionLow);
+			header.commands     = host_to_le(header.commands);
+			header.milliseconds = host_to_le(header.milliseconds);
 			fseek( handle, 0, SEEK_SET );
 			fwrite( &header, 1, sizeof( header ), handle );
 			fclose( handle );