Hi Hannes,
On Mon, 30 Jan 2017, Johannes Sixt wrote:
> 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.
I mistook "a" being used in sizeof(a) for breaking that assumption, but of
course a is *not* evaluated in that case. It is curious, though, that an
expression like "sizeof(a++)" would not be rejected.
Further, what would SWAP(a++, b) do? Swap a and b, and *then* increment a?
Ciao,
Johannes
