On Fri, 16 Sep 2016, Jonathan Wakely wrote:
On 16/09/16 09:04 +0200, Rainer Orth wrote:
Hi Jason,
OK, one more:
this works just fine on both sparc-sun-solaris2.12 and
i386-pc-solaris2.12.
Once Jonathan's patch to heed aligned_alloc's requirement on size being
a multiple of alignment is in, all is fine on Solaris.
I've got a slightly different fix now.
We only need to make the size a multiple of alignment for
aligned_alloc, however for posix_memalign we need to ensure the
alignment is a multiple of sizeof(void*).
I'm testing this now (but only on x86_64 GNU/Linux where it wasn't
failing anyway).
+ // The value of alignment shall be a power of two multiple of sizeof(void *).
+ if (al < sizeof(void*))
+ al = sizeof(void*);
The code doesn't exactly match the comment. I can't find the precondition
in the standard that says operator new can only be called on a power of
2... (maybe we can add it if it is really missing?)
Would using __builtin_expect (sz == 0, false) make sense? Surely it's
rare to try to allocate zero bytes.
https://gcc.gnu.org/ml/libstdc++/2014-03/msg00001.html
gcc already guesses that a test like sz == 0 is usually false (not with as
large a probability as if you use __builtin_expect, but enough that the
generated code is unlikely to differ). But adding __builtin_expect cannot
hurt...
Is the division (by a non-constant denominator) really necessary? Since
align has to be a power of 2, x % align should be the same as x & (align -
1), for instance.
I guess people interested in performance will do for aligned new the same
as for the old new: provide an inline version that skips all the overhead
to forward directly to malloc/aligned_alloc (and avoid questionable calls
in their code).
--
Marc Glisse
