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