std.math performance (SSE vs. real)

[Iain Buclaw via Digitalmars-d]

On 29 June 2014 23:20, H. S. Teoh via Digitalmars-d
<digitalmars-d at puremagic.com> wrote:
> On Sun, Jun 29, 2014 at 08:54:49AM +0100, Iain Buclaw via Digitalmars-d wrote:
>> On 29 Jun 2014 05:48, "H. S. Teoh via Digitalmars-d" <
>> digitalmars-d at puremagic.com> wrote:
>> >
>> > On Sat, Jun 28, 2014 at 08:41:24PM -0700, Andrei Alexandrescu via
>> Digitalmars-d wrote:
>> > > On 6/28/14, 6:02 PM, Tofu Ninja wrote:
>> > [...]
>> > > >I think this thread needs to refocus on the main point, getting
>> > > >math overloads for float and double and how to mitigate any
>> > > >problems that might arise from that.
>> > >
>> > > Yes please. -- Andrei
>> >
>> > Let's see the PR!
>> >
>>
>> I've already raised one (already linked in this thread).
>
> Are you talking about #2274? Interesting that your implementation is
> basically identical to my own idea for fixing std.math -- using unions
> instead of pointer casting.
>

Not really.  The biggest speed up was from adding float+double
overloads for floor, ceil, isNaN and isInfinity.  Firstly, the use of
a union itself didn't make much of a dent in the speed up.  Removing
the slow array copy operation did though.  Secondly, unions are
required for this particular function (floor) because we need to set
bits through type-punning, it just wouldn't work casting to a pointer.

Regards
Iain