DIP80: phobos additions

[Manu via Digitalmars-d]

On 10 June 2015 at 03:04, John Colvin via Digitalmars-d
<digitalmars-d at puremagic.com> wrote:
> On Tuesday, 9 June 2015 at 16:45:33 UTC, Manu wrote:
>>
>> On 10 June 2015 at 02:32, John Colvin via Digitalmars-d
>> <digitalmars-d at puremagic.com> wrote:
>>>
>>> On Tuesday, 9 June 2015 at 16:18:06 UTC, Manu wrote:
>>>>
>>>>
>>>> On 10 June 2015 at 01:26, Ilya Yaroshenko via Digitalmars-d
>>>> <digitalmars-d at puremagic.com> wrote:
>>>>>
>>>>> [...]
>>>>
>>>>
>>>>
>>>> A complication for linear algebra (or other mathsy things in general)
>>>> is the inability to detect and implement compound operations.
>>>> We don't declare mathematical operators to be algebraic operations,
>>>> which I think is a lost opportunity.
>>>> If we defined the properties along with their properties
>>>> (commutativity, transitivity, invertibility, etc), then the compiler
>>>> could potentially do an algebraic simplification on expressions before
>>>> performing codegen and optimisation.
>>>> There are a lot of situations where the optimiser can't simplify
>>>> expressions because it runs into an arbitrary function call, and I've
>>>> never seen an optimiser that understands exp/log/roots, etc, to the
>>>> point where it can reduce those expressions properly. To compete with
>>>> maths benchmarks, we need some means to simplify expressions properly.
>>>
>>>
>>>
>>> Optimising floating point is a massive pain because of precision concerns
>>> and IEEE-754 conformance. Just because something is analytically the same
>>> doesn't mean you want the optimiser to go ahead and make the switch for you.
>>
>>
>> We have flags to control this sort of thing (fast-math, strict ieee, etc).
>> I will worry about my precision, I just want the optimiser to do its
>> job and do the very best it possibly can. In the case of linear
>> algebra, the optimiser generally fails and I must manually simplify
>> expressions as much as possible.
>
>
> If the compiler is free to rewrite by analytical rules then "I will worry
> about my precision" is equivalent to either "I don't care about my
> precision" or "I have checked the codegen". A simple rearrangement of an
> expression can easily turn a perfectly good result in to complete garbage.
> It would be great if compilers were even better at fast-math mode, but an
> awful lot of applications can't use it.

This is fine, those applications would continue not to use it.
Personally, I've never written code in 20 years where I didn't want fast-math.