Index: configure.ac
==================================================================
--- configure.ac
+++ configure.ac
@@ -792,10 +792,32 @@
 ])
 
 AS_IF([test x"$enable_sockets" != x"no" -a x"$enable_threads" != x"no"], [
 	AC_SUBST(OFHTTPCLIENTTESTS_M, "OFHTTPClientTests.m")
 ])
+
+AC_DEFUN([CHECK_BUILTIN_BSWAP], [
+	AC_MSG_CHECKING(for __builtin_bswap$1)
+	AC_TRY_LINK([
+		#include <stdint.h>
+		#include <stdio.h>
+		#include <inttypes.h>
+		#include <errno.h>
+	], [
+		uint$1_t i = errno;
+		printf("%" PRIu$1, __builtin_bswap$1(i));
+	], [
+		AC_MSG_RESULT(yes)
+		AC_DEFINE(OF_HAVE_BUILTIN_BSWAP$1, 1,
+			[Whether we have __builtin_bswap$1])
+	], [
+		AC_MSG_RESULT(no)
+	])
+])
+CHECK_BUILTIN_BSWAP(16)
+CHECK_BUILTIN_BSWAP(32)
+CHECK_BUILTIN_BSWAP(64)
 
 case "$host" in
 	arm-apple-darwin*)
 		have_processes="no"
 		;;

Index: src/macros.h
==================================================================
--- src/macros.h
+++ src/macros.h
@@ -197,11 +197,13 @@
 }
 
 static OF_INLINE uint16_t OF_CONST_FUNC
 OF_BSWAP16_NONCONST(uint16_t i)
 {
-#if defined(OF_X86_64_ASM) || defined(OF_X86_ASM)
+#if defined(OF_HAVE_BUILTIN_BSWAP16)
+	return __builtin_bswap16(i);
+#elif defined(OF_X86_64_ASM) || defined(OF_X86_ASM)
 	__asm__ (
 	    "xchgb	%h0, %b0"
 	    : "=Q"(i)
 	    : "0"(i)
 	);
@@ -225,11 +227,13 @@
 }
 
 static OF_INLINE uint32_t OF_CONST_FUNC
 OF_BSWAP32_NONCONST(uint32_t i)
 {
-#if defined(OF_X86_64_ASM) || defined(OF_X86_ASM)
+#if defined(OF_HAVE_BUILTIN_BSWAP32)
+	return __builtin_bswap32(i);
+#elif defined(OF_X86_64_ASM) || defined(OF_X86_ASM)
 	__asm__ (
 	    "bswap	%0"
 	    : "=q"(i)
 	    : "0"(i)
 	);
@@ -255,11 +259,13 @@
 }
 
 static OF_INLINE uint64_t OF_CONST_FUNC
 OF_BSWAP64_NONCONST(uint64_t i)
 {
-#if defined(OF_X86_64_ASM)
+#if defined(OF_HAVE_BUILTIN_BSWAP64)
+	return __builtin_bswap64(i);
+#elif defined(OF_X86_64_ASM)
 	__asm__ (
 	    "bswap	%0"
 	    : "=r"(i)
 	    : "0"(i)
 	);

Index: src/objfw-defs.h.in
==================================================================
--- src/objfw-defs.h.in
+++ src/objfw-defs.h.in
@@ -1,10 +1,13 @@
 #undef OF_APPLE_RUNTIME
 #undef OF_BIG_ENDIAN
 #undef OF_FLOAT_BIG_ENDIAN
 #undef OF_HAVE_ASPRINTF
 #undef OF_HAVE_ATOMIC_OPS
+#undef OF_HAVE_BUILTIN_BSWAP16
+#undef OF_HAVE_BUILTIN_BSWAP32
+#undef OF_HAVE_BUILTIN_BSWAP64
 #undef OF_HAVE_CHMOD
 #undef OF_HAVE_CHOWN
 #undef OF_HAVE_COMPILER_TLS
 #undef OF_HAVE_FILES
 #undef OF_HAVE_FORWARDING_TARGET_FOR_SELECTOR