On 11/05/16 16:46, Joseph Myers wrote:
On Wed, 11 May 2016, Tejas Belagod wrote:
AFAICS, I don't think it mandates a double-rounding behavior for double to
__fp16 conversions and I don't see a change in stand between the two versions
of ACLE on the behavior of __fp16.
It's not a change between the two versions of ACLE. It's a change
relative to the early (pre-ACLE) __fp16 specification (or, at least, a
clarification thereto in email on 12 Aug 2008) that was used as a basis
for the original implementation of __fp16 in GCC (and that thus is what's
currently implemented by GCC and tested for in the testsuite).
Hi Joseph,
Sorry for the delay in responding.
I've had a conversation with Al and I now have some context. You're right - the
2008 mail you are referring to is the pre-ACLE behavior. By the time the first
draft of the first version of ACLE was reviewed by CodeSourcery(circa 2011), it
already mandated single rounding. No published ACLE has ever allowed double
rounding.
This meant that when the first draft of ACLE was published in 2011, its pre-ACLE
implementations in gcc and armcc were already non-conformant, in other words,
'bug-compatible'.
We do have plans to fix pre-ACLE behavior of fp16 to conform to current ACLE
spec, but can't say when exactly.
Thanks,
Tejas.