121 lines
4 KiB
C++
121 lines
4 KiB
C++
/*
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* SPDX-License-Identifier: GPL-2.0-or-later
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*
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* Copyright (C) 2020-2020 The dosbox-staging team
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License along
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* with this program; if not, write to the Free Software Foundation, Inc.,
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* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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*/
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#ifndef DOSBOX_BYTEORDER_H
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#define DOSBOX_BYTEORDER_H
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/* Usual way of handling endianess and byteswapping is via endian.h
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* (for e.g. htole* functions) or byteswap.h (e.g. bswap_16 macro).
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*
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* However, these headers are non-standard and almost every OS has their own
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* variations. It's easier to use compiler-provided intrinsics and builtins than
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* to rely on OS libraries.
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*
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* This header provides functions deliberately named differently
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* than popular variations on these implementations (e.g. bswap_u16 instead of
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* bswap_16), to avoid conflicts.
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*/
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#include "config.h"
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#include <cstdint>
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#include <cstdlib>
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#if !defined(_MSC_VER)
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/* Aside of MSVC, every C++11-capable compiler provides __builtin_bswap*
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* as compiler intrinsics or builtin functions.
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*/
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#define bswap_u16(x) __builtin_bswap16(x)
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#define bswap_u32(x) __builtin_bswap32(x)
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#define bswap_u64(x) __builtin_bswap64(x)
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#else
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/* MSVCS does not provide __builtin_bswap* functions, but has its own
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* byteswap builtin's. MSDN lists these as library functions, but MSVC makes
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* good job of inlinig them when compiling with /O2.
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*
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* https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/byteswap-uint64-byteswap-ulong-byteswap-ushort
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*/
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#define bswap_u16(x) _byteswap_ushort(x)
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#define bswap_u32(x) _byteswap_ulong(x)
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#define bswap_u64(x) _byteswap_uint64(x)
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#endif // MSC_VER
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#ifdef WORDS_BIGENDIAN
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#define host_to_le16(x) bswap_u16(static_cast<uint16_t>(x))
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#define host_to_le32(x) bswap_u32(static_cast<uint32_t>(x))
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#define host_to_le64(x) bswap_u64(static_cast<uint64_t>(x))
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#define le16_to_host(x) bswap_u16(static_cast<uint16_t>(x))
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#define le32_to_host(x) bswap_u32(static_cast<uint32_t>(x))
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#define le64_to_host(x) bswap_u64(static_cast<uint64_t>(x))
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#else
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#define host_to_le16(x) static_cast<uint16_t>(x)
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#define host_to_le32(x) static_cast<uint32_t>(x)
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#define host_to_le64(x) static_cast<uint64_t>(x)
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#define le16_to_host(x) static_cast<uint16_t>(x)
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#define le32_to_host(x) static_cast<uint32_t>(x)
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#define le64_to_host(x) static_cast<uint64_t>(x)
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#endif
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/* 'host_to_le' functions allow for byte order conversion on big endian
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* architectures while respecting memory alignment on low endian.
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*
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* We overload these functions to let compiler pick the correct byteswapping
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* function if user is ok with that.
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*
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* The only caveat in here is: MSVC bswap implementations are not constexpr,
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* so these functions won't compile using MSVC for big endian
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* architecture, but it's unlikely to ever be a real problem.
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*/
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constexpr uint8_t host_to_le(uint8_t x) noexcept { return x; }
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#ifdef WORDS_BIGENDIAN
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constexpr uint16_t host_to_le(uint16_t x) noexcept { return bswap_u16(x); }
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constexpr uint32_t host_to_le(uint32_t x) noexcept { return bswap_u32(x); }
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constexpr uint64_t host_to_le(uint64_t x) noexcept { return bswap_u64(x); }
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#else
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constexpr uint16_t host_to_le(uint16_t x) noexcept { return x; }
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constexpr uint32_t host_to_le(uint32_t x) noexcept { return x; }
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constexpr uint64_t host_to_le(uint64_t x) noexcept { return x; }
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#endif
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/* Functions 'le_to_host' and 'host_to_le' are the same function, only the user
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* intent might be different.
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*/
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#define le_to_host(x) host_to_le(x)
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#endif
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