#include <folly/Likely.h>
#include <cassert>
+#include <cstring>
#include <cinttypes>
#include <iterator>
#include <limits>
*/
namespace detail {
-template <class T>
-struct EndianIntBase {
- public:
- static T swap(T x);
-};
+template <size_t Size>
+struct uint_types_by_size;
-#define FB_GEN(t, fn) \
- template <> \
- inline t EndianIntBase<t>::swap(t x) { \
- return t(fn(std::make_unsigned<t>::type(x))); \
- }
+#define FB_GEN(sz, fn) \
+ static inline uint##sz##_t byteswap_gen(uint##sz##_t v) { \
+ return fn(v); \
+ } \
+ template <> \
+ struct uint_types_by_size<sz> { \
+ using type = uint##sz##_t; \
+ };
-// fn(x) expands to (x) if the second argument is empty, which is exactly
-// what we want for [u]int8_t.
-FB_GEN( int8_t,)
-FB_GEN(uint8_t,)
+FB_GEN(8, uint8_t)
#ifdef _MSC_VER
-FB_GEN( int64_t, _byteswap_uint64)
-FB_GEN(uint64_t, _byteswap_uint64)
-FB_GEN( int32_t, _byteswap_ulong)
-FB_GEN(uint32_t, _byteswap_ulong)
-FB_GEN( int16_t, _byteswap_ushort)
-FB_GEN(uint16_t, _byteswap_ushort)
+FB_GEN(64, _byteswap_uint64)
+FB_GEN(32, _byteswap_ulong)
+FB_GEN(16, _byteswap_ushort)
#else
-FB_GEN( int64_t, __builtin_bswap64)
-FB_GEN(uint64_t, __builtin_bswap64)
-FB_GEN( int32_t, __builtin_bswap32)
-FB_GEN(uint32_t, __builtin_bswap32)
-FB_GEN( int16_t, __builtin_bswap16)
-FB_GEN(uint16_t, __builtin_bswap16)
+FB_GEN(64, __builtin_bswap64)
+FB_GEN(32, __builtin_bswap32)
+FB_GEN(16, __builtin_bswap16)
#endif
#undef FB_GEN
template <class T>
-struct EndianInt : public EndianIntBase<T> {
- public:
+struct EndianInt {
+ static_assert(
+ (std::is_integral<T>::value && !std::is_same<T, bool>::value) ||
+ std::is_floating_point<T>::value,
+ "template type parameter must be non-bool integral or floating point");
+ static T swap(T x) {
+ // we implement this with memcpy because that is defined behavior in C++
+ // we rely on compilers to optimize away the memcpy calls
+ constexpr auto s = sizeof(T);
+ using B = typename uint_types_by_size<8 * s>::type;
+ B b;
+ std::memcpy(&b, &x, s);
+ b = byteswap_gen(b);
+ std::memcpy(&x, &b, s);
+ return x;
+ }
static T big(T x) {
return kIsLittleEndian ? EndianInt::swap(x) : x;
}
#include <folly/Bits.h>
+#include <random>
+
#include <folly/portability/GTest.h>
using namespace folly;
EXPECT_EQ(32, popcount(uint32_t(-1)));
EXPECT_EQ(64, popcount(uint64_t(-1)));
}
+
+TEST(Bits, Endian_swap_uint) {
+ EXPECT_EQ(uint8_t(0xda), Endian::swap(uint8_t(0xda)));
+ EXPECT_EQ(uint16_t(0x4175), Endian::swap(uint16_t(0x7541)));
+ EXPECT_EQ(uint32_t(0x42efb918), Endian::swap(uint32_t(0x18b9ef42)));
+ EXPECT_EQ(
+ uint64_t(0xa244f5e862c71d8a), Endian::swap(uint64_t(0x8a1dc762e8f544a2)));
+}
+
+TEST(Bits, Endian_swap_real) {
+ std::mt19937_64 rng;
+ auto f = std::uniform_real_distribution<float>()(rng);
+ EXPECT_NE(f, Endian::swap(f));
+ EXPECT_EQ(f, Endian::swap(Endian::swap(f)));
+ auto d = std::uniform_real_distribution<double>()(rng);
+ EXPECT_NE(d, Endian::swap(d));
+ EXPECT_EQ(d, Endian::swap(Endian::swap(d)));
+}