Am 31.01.2017 um 13:13 schrieb Johannes Schindelin:
Hi René,
On Mon, 30 Jan 2017, René Scharfe wrote:
Am 30.01.2017 um 21:48 schrieb Johannes Schindelin:
The commit you quoted embarrasses me, and I have no excuse for it. I
would love to see that myswap() ugliness fixed by replacing it with a
construct that is simpler, and generates good code even without any
smart compiler.
I don't see a way to do that without adding a type parameter.
Exactly. And you know what? I would be very okay with that type parameter.
Coccinelle [*1*] should be able to cope with that, too, mehtinks.
Yes, a semantic patch can turn the type of the temporary variable into a
macro parameter. Programmers would have to type the type, though,
making the macro only half as good.
It would be trivially "optimized" out of the box, even when compiling with
Tiny C or in debug mode.
Such a compiler is already slowed down by memset(3) calls for
initializing objects and lack of other optimizations. I doubt a few
more memcpy(3) calls would make that much of a difference.
NB: git as compiled with TCC fails several tests, alas. Builds wickedly
fast, though.
And it would even allow things like this:
#define SIMPLE_SWAP(T, a, b) do { T tmp_ = a; a = b; b = tmp_; } while (0)
...
uint32_t large;
char nybble;
...
if (!(large & ~0xf)) {
SIMPLE_SWAP(char, nybble, large);
...
}
i.e. mixing types, when possible.
And while I do not necessarily expect that we need anything like this
anytime soon, merely the fact that it allows for this flexibility, while
being very readable at the same time, would make it a pretty good design
in my book.
Such a skinny macro which only hides repetition is kind of attractive
due to its simplicity; I can't say the same about the mixed type example
above, though.
The fat version isn't that bad either even without inlining, includes a
few safety checks and doesn't require us to tell the compiler something
it already knows very well. I'd rather let the machine do the work.
René