endianness.h

/*
 * Copyright (c) 2017, Matias Fontanini
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 * 
 * * Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * * Redistributions in binary form must reproduce the above
 *   copyright notice, this list of conditions and the following disclaimer
 *   in the documentation and/or other materials provided with the
 *   distribution.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 */
 
#ifndef TINS_ENDIANNESS_H
#define TINS_ENDIANNESS_H

#include <stdint.h>
#include <tins/macros.h>

#if defined(__APPLE__)
    #include <sys/types.h>
    #define TINS_IS_LITTLE_ENDIAN (BYTE_ORDER == LITTLE_ENDIAN)
    #define TINS_IS_BIG_ENDIAN (BYTE_ORDER == BIG_ENDIAN)
#elif defined(BSD)
    #include <sys/endian.h>
    #define TINS_IS_LITTLE_ENDIAN (_BYTE_ORDER == _LITTLE_ENDIAN)
    #define TINS_IS_BIG_ENDIAN (_BYTE_ORDER == _BIG_ENDIAN)
#elif defined(_WIN32)
    #include <cstdlib>
    // Assume windows == little endian. fixme later
    #define TINS_IS_LITTLE_ENDIAN 1
    #define TINS_IS_BIG_ENDIAN 0
#else
    #include <endian.h>
    #define TINS_IS_LITTLE_ENDIAN (__BYTE_ORDER == __LITTLE_ENDIAN)
    #define TINS_IS_BIG_ENDIAN (__BYTE_ORDER == __BIG_ENDIAN)
#endif

// Define macros to swap bytes using compiler intrinsics when possible
#if defined(_MSC_VER)
    #define TINS_BYTE_SWAP_16(data) _byteswap_ushort(data)
    #define TINS_BYTE_SWAP_32(data) _byteswap_ulong(data)
    #define TINS_BYTE_SWAP_64(data) _byteswap_uint64(data)
#elif defined(TINS_HAVE_GCC_BUILTIN_SWAP)
    #define TINS_BYTE_SWAP_16(data) __builtin_bswap16(data)
    #define TINS_BYTE_SWAP_32(data) __builtin_bswap32(data)
    #define TINS_BYTE_SWAP_64(data) __builtin_bswap64(data)
#else
    #define TINS_NO_BYTE_SWAP_INTRINSICS
#endif

namespace Tins {
namespace Endian {

inline uint8_t do_change_endian(uint8_t data) {
    return data;
}

inline uint16_t do_change_endian(uint16_t data) {
    #ifdef TINS_NO_BYTE_SWAP_INTRINSICS
        return ((data & 0xff00) >> 8)  | ((data & 0x00ff) << 8);
    #else
        return TINS_BYTE_SWAP_16(data);
    #endif
}

inline uint32_t do_change_endian(uint32_t data) {
    #ifdef TINS_NO_BYTE_SWAP_INTRINSICS
        return (((data & 0xff000000) >> 24) | ((data & 0x00ff0000) >> 8)  |
               ((data & 0x0000ff00) << 8)  | ((data & 0x000000ff) << 24));
    #else
        return TINS_BYTE_SWAP_32(data);
    #endif
}

 inline uint64_t do_change_endian(uint64_t data) {
    #ifdef TINS_NO_BYTE_SWAP_INTRINSICS
        return (((uint64_t)(do_change_endian((uint32_t)(data & 0xffffffff))) << 32) |
               (do_change_endian(((uint32_t)(data >> 32)))));
    #else
        return TINS_BYTE_SWAP_64(data);
    #endif
 }
 
// Helpers to convert
template<typename T>
struct conversion_dispatch_helper {
    static T dispatch(T data) {
        return do_change_endian(data);
    }
};


template<size_t>
struct conversion_dispatcher;

template<>
struct conversion_dispatcher<sizeof(uint8_t)> 
: public conversion_dispatch_helper<uint8_t> { };

template<>
struct conversion_dispatcher<sizeof(uint16_t)> 
: public conversion_dispatch_helper<uint16_t> { };

template<>
struct conversion_dispatcher<sizeof(uint32_t)> 
: public conversion_dispatch_helper<uint32_t> { };

template<>
struct conversion_dispatcher<sizeof(uint64_t)> 
: public conversion_dispatch_helper<uint64_t> { };

 template<typename T>
 inline T change_endian(T data) {
     return conversion_dispatcher<sizeof(T)>::dispatch(data);
 }

#if TINS_IS_LITTLE_ENDIAN

    template<typename T>
    inline T host_to_be(T data) {
        return change_endian(data);
    }
     
     template<typename T>
     inline T host_to_le(T data) {
         return data;
     }
     
     template<typename T>
     inline T be_to_host(T data) {
         return change_endian(data);
     }
     
     template<typename T>
     inline T le_to_host(T data) {
         return data;
     }
#elif TINS_IS_BIG_ENDIAN

    template<typename T>
    inline T host_to_be(T data) {
        return data;
    }
     
     template<typename T>
     inline T host_to_le(T data) {
         return change_endian(data);
     }
     
     template<typename T>
     inline T be_to_host(T data) {
         return data;
     }
     
     template<typename T>
     inline T le_to_host(T data) {
         return change_endian(data);
     }
#endif
     
} // Endian
} // Tins

#endif // TINS_ENDIANNESS_H