std.math API rework

[Iain Buclaw via Digitalmars-d]

On 6 October 2016 at 22:55, Ilya Yaroshenko via Digitalmars-d
<digitalmars-d at puremagic.com> wrote:
> On Thursday, 6 October 2016 at 20:45:24 UTC, Iain Buclaw wrote:
>>
>> On 6 October 2016 at 22:31, Ilya Yaroshenko via Digitalmars-d
>> <digitalmars-d at puremagic.com> wrote:
>>>
>>> On Thursday, 6 October 2016 at 20:07:19 UTC, Iain Buclaw wrote:
>>>>
>>>>
>>>> On 6 October 2016 at 18:53, Ilya Yaroshenko via Digitalmars-d
>>>> <digitalmars-d at puremagic.com> wrote:
>>>>>
>>>>>
>>>>> [...]
>>>>
>>>>
>>>>
>>>> If you can prove that llvm intrinsics are pure (gcc math intrinsics are
>>>> not) and that llvm intrinsics pass the unittest (gcc math intrinsics aren't
>>>> guaranteed to due to the vagary of libm implementations and quirky cpu
>>>> support that trades correctness for efficiency).
>>>>
>>>> [...]
>>>
>>>
>>>
>>> LLVM math functions are pure :P http://llvm.org/docs/LangRef.html
>>>
>>
>> I picked a random example.
>>
>> http://llvm.org/docs/LangRef.html#llvm-sin-intrinsic
>>
>> """
>>
>> Semantics:
>>
>> This function returns the sine of the specified operand, returning the
>> same values as the libm sin functions would, and handles error conditions in
>> the same way.
>>
>> """
>>
>> This would have me believe that they are infact not pure. ;-)
>>
>> But, I've never looked under the hood of LLVM, so I can only believe those
>> who have.  In any case, IMO, you should focus on getting this into
>> core.math.  That's where compiler intrinsics should go.  The intrinsics of
>> std.math are historical baggage and are probably due a deprecation - that
>> is, in the sense that their symbols be converted into aliases.
>>
>> Iain.
>
>
> Current code is (please look in LDC's fork):
>
> version(LDC)
> {
>     real   cos(real   x) @safe pure nothrow @nogc { return llvm_cos(x); }
>     ///ditto
>     double cos(double x) @safe pure nothrow @nogc { return llvm_cos(x); }
>     ///ditto
>     float  cos(float  x) @safe pure nothrow @nogc { return llvm_cos(x); }
> }
> else
> {
>
> real cos(real x) @safe pure nothrow @nogc { pragma(inline, true); return
> core.math.cos(x); }
> //FIXME
> ///ditto
> double cos(double x) @safe pure nothrow @nogc { return cos(cast(real)x); }
> //FIXME
> ///ditto
> float cos(float x) @safe pure nothrow @nogc { return cos(cast(real)x); }
>
> }
>
> So, I don't see a reason why this change break something, hehe

Well, sure, I could mark all gcc intrinsics as pure so you can use
__builtin_print() or malloc() in pure code.  Doesn't mean the compiler
is honest in allowing it. ;-)

Get this in core.math, there's no place for compiler-specific code in phobos.

Iain.