Rework intrinsic.hpp to handle GCC and Clang __builtin_bswap* if available. Add test program.

test/converter_test.cpp

@@ -239,6 +239,8 @@ namespace
 
 int cpp_main(int, char * [])
 {
+  cout << "byte swap intrinsics: " BOOST_ENDIAN_INTRINSIC_MSG << endl;
+  
   //std::cerr << std::hex;
 
   cout << "int16_t" << endl;

test/intrinsic_test.cpp

@@ -0,0 +1,24 @@
+//  Copyright Beman Dawes 2013
+
+//  Distributed under the Boost Software License, Version 1.0.
+//  http://www.boost.org/LICENSE_1_0.txt
+
+#include "intrinsic.hpp"
+#include <iostream>
+#include <cassert>
+#include <cstdint>
+
+int main()
+{
+  std::cout << "BOOST_ENDIAN_INTRINSIC_MSG: " BOOST_ENDIAN_INTRINSIC_MSG << std::endl;
+
+#ifndef BOOST_ENDIAN_NO_INTRINSICS
+  uint16_t x2 = 0x1122U;
+  assert(BOOST_ENDIAN_INTRINSIC_BYTE_SWAP_2(x2) == 0x2211U);
+  uint32_t x4 = 0x11223344UL;
+  assert(BOOST_ENDIAN_INTRINSIC_BYTE_SWAP_4(x4) == 0x44332211UL);
+  uint64_t x8 = 0x1122334455667788U;
+  assert(BOOST_ENDIAN_INTRINSIC_BYTE_SWAP_8(x8) == 0x8877665544332211ULL);
+#endif
+  return 0;
+}