On Thursday, 02 June 2005, at 15:56:40 (-0400),
John Ellson wrote:
> RCS file: /cvsroot/enlightenment/eterm/libast/configure.in,v
> retrieving revision 1.24
Got it, thanks.
On Thursday, 02 June 2005, at 16:02:00 (-0400),
Mike Frysinger wrote:
> would an ifdef like:
> #if STRICT_ISO_C99 || __GNUC__ > 4
> be unacceptable ? that way the installed libast wouldnt need to be
> reconfigured/built/installed just to change STRICT_ISO_C99 ...
How about this:
#ifdef __GNUC__
# if __GNUC__ >= 4
# define STRICT_ISO_C99
# fi
...
#endif
On Thursday, 02 June 2005, at 18:39:01 (-0600),
Tres Melton wrote:
> #define BINSWAP(a, b) \
> (((long) (a)) ^= ((long) (b)) ^= ((long) (a)) ^= ((long) (b)))
>
> int main( void )
> {
> long a = 3;
> long b = 8;
>
> asm( "noop;noop;noop" );
> BINSWAP(a,b);
> asm( "noop;noop;noop" );
>
> }
>
> yields:
>
> noop;noop;noop
> movq -16(%rbp), %rdx
> leaq -8(%rbp), %rax
> xorq %rdx, (%rax)
> movq -8(%rbp), %rdx
> leaq -16(%rbp), %rax
> xorq %rdx, (%rax)
> movq -16(%rbp), %rdx
> leaq -8(%rbp), %rax
> xorq %rdx, (%rax)
> noop;noop;noop
>
> If you enable -O[123] then you will need to use the values a & b before
> and after the BINSWAP call or they will be optimized away. And simply
> using immediate values like I did will cause the compiler to simply set
> the different registers that are used to access them in reverse order.
> In other words the swap gets optimized out. The above code is without
> -O and is clearly more complicated (by more than double) than it needs
> to be.
Interesting. You think I should just get rid of it then?
On Thursday, 02 June 2005, at 21:04:59 (-0400),
John Ellson wrote:
> I understand that this is a ISO C99 restriction and that gcc4 is
> just a bit more pedantic than gcc3.
gcc4 does C99 by default now, does it not?
> In fact my first attempt at a fix was to just not use the xor
> BINSWAP macro at all, but this is really a question for Michael. I
> was just trying to get his code to compile.
It's actually slower normally but faster optimized:
-O0
Profiling SWAP() macro...3000000 iterations in 0.052468 seconds, 1.7489e-08
seconds per iteration
Profiling BINSWAP() macro...3000000 iterations in 0.067905 seconds, 2.2635e-08
seconds per iteration
-O2
Profiling SWAP() macro...3000000 iterations in 0.014328 seconds, 4.776e-09
seconds per iteration
Profiling BINSWAP() macro...3000000 iterations in 0.014183 seconds, 4.7277e-09
seconds per iteration
(Done with libast's "make perf")
Michael
--
Michael Jennings (a.k.a. KainX) http://www.kainx.org/ <[EMAIL PROTECTED]>
n + 1, Inc., http://www.nplus1.net/ Author, Eterm (www.eterm.org)
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