On 16/09/16 13:12 +0100, Jonathan Wakely wrote:
On 16/09/16 11:56 +0100, Jonathan Wakely wrote:
On 16/09/16 11:37 +0200, Marc Glisse wrote:
Is the division (by a non-constant denominator) really necessary?
Probably not, but I've asked the committee for clarification what this
function should do when called with an invalid alignment.
Since align has to be a power of 2, x % align should be the same
as x & (align - 1), for instance.
Thanks, if it's UB to call it with alignments that aren't a power of
two then we can do that.
I've committed the patch now, to fix the failures for Solaris. I'll
revisit it when I get clarification from the committee about invalid
alignment arguments.
I missed 18.6.2/1 which is clear that we don't have to support invalid
alignments passed to operator new, so I'm committing this.
Tested x86_64-linux.
commit 0a70fa595953ff1e6e46266d7f86bc6d7e3400a4
Author: Jonathan Wakely <jwak...@redhat.com>
Date: Fri Sep 16 17:36:44 2016 +0100
Replace modulus with mask operation in over-aligned new
2016-09-16 Jonathan Wakely <jwak...@redhat.com>
Marc Glisse <marc.gli...@inria.fr>
* libsupc++/new_opa.cc [_GLIBCXX_HAVE_ALIGNED_ALLOC]
(operator new(size_t, align_val_t)): Replace modulus operator with
mask.
diff --git a/libstdc++-v3/libsupc++/new_opa.cc b/libstdc++-v3/libsupc++/new_opa.cc
index 9c859c1..91e53a8 100644
--- a/libstdc++-v3/libsupc++/new_opa.cc
+++ b/libstdc++-v3/libsupc++/new_opa.cc
@@ -69,7 +69,7 @@ operator new (std::size_t sz, std::align_val_t al)
#if _GLIBCXX_HAVE_ALIGNED_ALLOC
/* C11: the value of size shall be an integral multiple of alignment. */
- if (std::size_t rem = sz % align)
+ if (std::size_t rem = sz & (align - 1))
sz += align - rem;
#endif
