Uses built-in byte swap if available (Apple) and if bswap_XX is undefined

src/qt/test/compattests.cpp

@@ -0,0 +1,23 @@
+// Copyright (c) 2016 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include "paymentrequestplus.h" // this includes protobuf's port.h which defines its own bswap macos
+
+#include "compattests.h"
+
+#include "compat/byteswap.h"
+
+void CompatTests::bswapTests()
+{
+	// Sibling in bitcoin/src/test/bswap_tests.cpp
+	uint16_t u1 = 0x1234;
+	uint32_t u2 = 0x56789abc;
+	uint64_t u3 = 0xdef0123456789abc;
+	uint16_t e1 = 0x3412;
+	uint32_t e2 = 0xbc9a7856;
+	uint64_t e3 = 0xbc9a78563412f0de;
+	QVERIFY(bswap_16(u1) == e1);
+	QVERIFY(bswap_32(u2) == e2);
+	QVERIFY(bswap_64(u3) == e3);
+}