libcruft-util/endian.hpp

147 lines
4.7 KiB
C++

/*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
* Copyright 2010-2014 Danny Robson <danny@nerdcruft.net>
*/
#ifndef __UTIL_ENDIAN_HPP
#define __UTIL_ENDIAN_HPP
#include "types/bits.hpp"
#include <cstdint>
#include <type_traits>
namespace util {
//-------------------------------------------------------------------------
// Uses the TIFF header values. Just because. Don't rely on this.
enum class endian : uint16_t {
BIG = 0x4D4D,
LITTLE = 0x4949,
};
//-------------------------------------------------------------------------
template <typename T>
constexpr T
bswap (T) noexcept;
// CXX: Update using "if constexpr" when available. It doesn't seem to be
// worth the dicking about to use enable_if_t to differentiate the
// signed/unsigned cases.
#define SIGNED_BSWAP(S) \
template <> \
constexpr \
int##S##_t \
bswap (int##S##_t v) noexcept { \
const union { \
int##S##_t s; \
uint##S##_t u; \
} vu = { v }; \
\
return __builtin_bswap##S (vu.u); \
}
SIGNED_BSWAP(16)
SIGNED_BSWAP(32)
SIGNED_BSWAP(64)
template <> constexpr int8_t bswap ( int8_t v) noexcept { return v; }
template <> constexpr uint8_t bswap (uint8_t v) noexcept { return v; }
template <> constexpr uint16_t bswap (uint16_t v) noexcept { return __builtin_bswap16 (v); }
template <> constexpr uint32_t bswap (uint32_t v) noexcept { return __builtin_bswap32 (v); }
template <> constexpr uint64_t bswap (uint64_t v) noexcept { return __builtin_bswap64 (v); }
// use a type-punning union to punt the byte swapping operation to the
// unsigned integer code.
//
// this is debatably safe under production compilers like gcc + clang
// despite what the standard may say about unions.
template <>
constexpr float
bswap (float v) noexcept
{
union {
float f;
uint32_t u;
} temp { .f = v };
temp.u = bswap (temp.u);
return temp.f;
}
//-------------------------------------------------------------------------
template <typename T>
constexpr T
identity (T &&v) {
return v;
}
//-------------------------------------------------------------------------
#if defined(WORDS_BIGENDIAN)
template <typename T> constexpr T hton (T v) { return v; }
template <typename T> constexpr T ntoh (T v) { return v; }
template <typename T> constexpr T htob (T v) { return v; }
template <typename T> constexpr T htol (T v) { return bswap (v); }
template <typename T> constexpr T btoh (T v) { return v; }
template <typename T> constexpr T ltoh (T v) { return bswap (v); }
#else
template <typename T> constexpr T hton (T v) { return bswap (v); }
template <typename T> constexpr T ntoh (T v) { return bswap (v); }
template <typename T> constexpr T htob (T v) { return bswap (v); }
template <typename T> constexpr T htol (T v) { return v; }
template <typename T> constexpr T btoh (T v) { return bswap (v); }
template <typename T> constexpr T ltoh (T v) { return v; }
#endif
//-------------------------------------------------------------------------
struct from_endian {
explicit from_endian (endian _endian):
src (_endian)
{ ; }
template <typename T>
T operator() (const T v) const {
static_assert (std::is_integral<T>::value || std::is_enum<T>::value,
"endian conversion is only defined for integrals currently");
union {
typename sized_type<T>::sint sint;
typename sized_type<T>::uint uint;
};
if (std::is_signed<T>::value)
sint = v;
else
uint = v;
uint = (src == endian::LITTLE) ? ltoh (uint) : btoh (uint);
if (std::is_signed<T>::value)
return T (sint);
else
return T (uint);
}
endian src;
};
}
#endif