Hi Joe,
On Apr 13, 2016, at 3:02 PM, Joseph D. Darcy <[email protected]> wrote:
> On 4/13/2016 12:43 PM, Brian Burkhalter wrote:
>>
>> A couple of points of curiosity. Firstly, is this not “fused multiply-add”
>> rather than “fused multiply-accumulate?” Secondly, why the choice of name
>> “fusedMac()” instead of the common “fma()” or the longer but perhaps clearer
>> “fusedMultiplyAdd()?”
>
> On naming, there are a few candidates. As background, I'll note that the
> naming in java.lang.Math at times follows the C-style naming ("cos" rather
> than "cosine"), but that methods we've added more recently outside of the
> traditional C math.h have followed more Java-style conventions. FWIW, C99
> calls this "fma".
>
> So, "fma()" is a possible choice, certainly concise, but I don't think many
> people would find it very suggestive as to what it does, at least not with
> the current familiarity with fused multiply-add.
>
> In the IEEE 754 2008 standard, the operation is spelled out as
> "fusedMultiplyAdd", but that is a bit long.
>
> The "multiply accumulate" term is how I first heard of the operation and
> there is some other usage of it
> (https://en.wikipedia.org/wiki/Multiply%E2%80%93accumulate_operation), but
> "fused multiply add" is also an accurate description.
Yes, I saw this latter as well. It is the mention of the accumulator there
which made me think that multiply-add is more apt.
> As part of favoring "simplicity over speed," I intentionally wrote the code
> in a way that tried to follow the structure of the specification in a
> straightforward manner. […] For this initial implementation, I think this
> kind of simplicity is desirable. Longer term, I wouldn't be surprised if this
> implementation was retired out to be a reference implementation for
> additional regression tests.
Well that is a good point: if the eventual target is an intrinsic or other
accelerated implementation then this probably does not matter that much.
Brian
