From: Johannes Sixt <j6t@kdbg.org>
Date: Mon, 30 Jan 2017 18:41:37 GMT
Subject: Re: [PATCH 1/5] add SWAP macro
Message-ID: <aa653d57-4a97-ac50-b20c-f94ed43a22fb@kdbg.org>
In-Reply-To: <alpine.DEB.2.20.1701301643260.3469@virtualbox>

Am 30.01.2017 um 17:01 schrieb Johannes Schindelin:
> On Sat, 28 Jan 2017, René Scharfe wrote:
>> diff --git a/git-compat-util.h b/git-compat-util.h
>> index 87237b092b..66cd466eea 100644
>> --- a/git-compat-util.h
>> +++ b/git-compat-util.h
>> @@ -527,6 +527,16 @@ static inline int ends_with(const char *str, const char *suffix)
>>  	return strip_suffix(str, suffix, &len);
>>  }
>>
>> +#define SWAP(a, b) do {						\
>> +	void *_swap_a_ptr = &(a);				\
>> +	void *_swap_b_ptr = &(b);				\
>> +	unsigned char _swap_buffer[sizeof(a)];			\
>> +	memcpy(_swap_buffer, _swap_a_ptr, sizeof(a));		\
>> +	memcpy(_swap_a_ptr, _swap_b_ptr, sizeof(a) +		\
>> +	       BUILD_ASSERT_OR_ZERO(sizeof(a) == sizeof(b)));	\
>> +	memcpy(_swap_b_ptr, _swap_buffer, sizeof(a));		\
>> +} while (0)
>> +
>>  #if defined(NO_MMAP) || defined(USE_WIN32_MMAP)
>
> It may seem as a matter of taste, or maybe not: I prefer this without the
> _swap_a_ptr

The purpose of these pointers is certainly to avoid that the macro 
arguments are evaluated more than once.

-- Hannes