common: add va_args.h

This PR is upstreaming changes in the Seraphis lib here: https://github.com/UkoeHB/monero/pull/39. This header adds a macro `VA_ARGS_COMMAPREFIX`
which, when passed `__VA_ARGS__`, expands to `, __VA_ARGS__` unless the length of `__VA_ARGS__` is 0, in which case it expands to nothing. This
macro is useful for passing/declaring optional function arguments.
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jeffro256 2024-04-11 11:32:03 -05:00
parent c8214782fb
commit bc05e724cb
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// Copyright (c) 2024, The Monero Project
//
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without modification, are
// permitted provided that the following conditions are met:
//
// 1. Redistributions of source code must retain the above copyright notice, this list of
// conditions and the following disclaimer.
//
// 2. 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.
//
// 3. Neither the name of the copyright holder nor the names of its contributors may be
// used to endorse or promote products derived from this software without specific
// prior written permission.
//
// 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 HOLDER 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.
#pragma once
// Check for __VA_OPT__ support
// Apdated from cpplearner's StackOverflow answer: https://stackoverflow.com/a/48045656
#define PP_THIRD_ARG(a,b,c,...) c
#define VA_OPT_SUPPORTED_I(...) PP_THIRD_ARG(__VA_OPT__(,),true,false,)
#define VA_OPT_SUPPORTED VA_OPT_SUPPORTED_I(?)
// VA_ARGS_COMMAPREFIX(): VA_ARGS_COMMAPREFIX(__VA_ARGS__) expands to __VA_ARGS__ with a comma in
// front if more than one argument, else nothing.
// If __VA_OPT__ supported, use that. Else, use GCC's ,## hack
#if VA_OPT_SUPPORTED
# define VA_ARGS_COMMAPREFIX(...) __VA_OPT__(,) __VA_ARGS__
#else
# define VA_ARGS_COMMAPREFIX(...) , ## __VA_ARGS__
#endif