On linux x86_64 : real.sizeof == 16 but it looks like only the first the first 10 bytes are used (ie. 80bits)

Is there a way to know the real size of a real ?

On Monday, 24 August 2015 at 21:55:40 UTC, Guillaume Chatelet wrote:
> On linux x86_64 : real.sizeof == 16 but it looks like only the first the first 10 bytes are used (ie. 80bits)
>
> Is there a way to know the real size of a real ?

http://dlang.org/type.html
	largest FP size implemented in hardwareImplementation Note: 80 bits for x86 CPUs or double size, whichever is larger

On Monday, 24 August 2015 at 21:58:48 UTC, rsw0x wrote:
> On Monday, 24 August 2015 at 21:55:40 UTC, Guillaume Chatelet wrote:
>> On linux x86_64 : real.sizeof == 16 but it looks like only the first the first 10 bytes are used (ie. 80bits)
>>
>> Is there a way to know the real size of a real ?
>
> http://dlang.org/type.html
> 	largest FP size implemented in hardwareImplementation Note: 80 bits for x86 CPUs or double size, whichever is larger

Yep I found this, I'd like to know this information at compile time.

On Monday, 24 August 2015 at 22:08:03 UTC, Guillaume Chatelet wrote:
> On Monday, 24 August 2015 at 21:58:48 UTC, rsw0x wrote:
>> On Monday, 24 August 2015 at 21:55:40 UTC, Guillaume Chatelet wrote:
>>> On linux x86_64 : real.sizeof == 16 but it looks like only the first the first 10 bytes are used (ie. 80bits)
>>>
>>> Is there a way to know the real size of a real ?
>>
>> http://dlang.org/type.html
>> 	largest FP size implemented in hardwareImplementation Note: 80 bits for x86 CPUs or double size, whichever is larger
>
> Yep I found this, I'd like to know this information at compile time.

I actually found another way(1) but if someone knows how to get this information at compile time I'm still interested. Thx !

1. https://github.com/D-Programming-Language/dmd/pull/4952

On Monday, 24 August 2015 at 22:08:03 UTC, Guillaume Chatelet wrote:
> On Monday, 24 August 2015 at 21:58:48 UTC, rsw0x wrote:
>> On Monday, 24 August 2015 at 21:55:40 UTC, Guillaume Chatelet wrote:
>>> On linux x86_64 : real.sizeof == 16 but it looks like only the first the first 10 bytes are used (ie. 80bits)
>>>
>>> Is there a way to know the real size of a real ?
>>
>> http://dlang.org/type.html
>> 	largest FP size implemented in hardwareImplementation Note: 80 bits for x86 CPUs or double size, whichever is larger
>
> Yep I found this, I'd like to know this information at compile time.

Oh, my apologies. I've looked around and I can't seem to find anything.
Sorry for the noise.

On Monday, 24 August 2015 at 21:55:40 UTC, Guillaume Chatelet wrote:
> On linux x86_64 : real.sizeof == 16 but it looks like only the first the first 10 bytes are used (ie. 80bits)
>
> Is there a way to know the real size of a real ?

The best I can think of is to use the mant_dig property which returns the number of bits in the mantissa.

http://dpaste.dzfl.pl/9889b3d0bd5b

On 25-Aug-2015 01:29, Guillaume Chatelet wrote:
> On Monday, 24 August 2015 at 22:08:03 UTC, Guillaume Chatelet wrote:
>> On Monday, 24 August 2015 at 21:58:48 UTC, rsw0x wrote:
>>> On Monday, 24 August 2015 at 21:55:40 UTC, Guillaume Chatelet wrote:
>>>> On linux x86_64 : real.sizeof == 16 but it looks like only the first
>>>> the first 10 bytes are used (ie. 80bits)
>>>>
>>>> Is there a way to know the real size of a real ?
>>>
>>> http://dlang.org/type.html
>>>     largest FP size implemented in hardwareImplementation Note: 80
>>> bits for x86 CPUs or double size, whichever is larger
>>
>> Yep I found this, I'd like to know this information at compile time.
>
> I actually found another way(1) but if someone knows how to get this
> information at compile time I'm still interested. Thx !
>
> 1. https://github.com/D-Programming-Language/dmd/pull/4952

real.sizeof ?

-- 
Dmitry Olshansky

On 25-Aug-2015 08:28, Dmitry Olshansky wrote:
> On 25-Aug-2015 01:29, Guillaume Chatelet wrote:
>> On Monday, 24 August 2015 at 22:08:03 UTC, Guillaume Chatelet wrote:
>>> On Monday, 24 August 2015 at 21:58:48 UTC, rsw0x wrote:
>>>> On Monday, 24 August 2015 at 21:55:40 UTC, Guillaume Chatelet wrote:
>>>>> On linux x86_64 : real.sizeof == 16 but it looks like only the first
>>>>> the first 10 bytes are used (ie. 80bits)
>>>>>
>>>>> Is there a way to know the real size of a real ?
>>>>
>>>> http://dlang.org/type.html
>>>>     largest FP size implemented in hardwareImplementation Note: 80
>>>> bits for x86 CPUs or double size, whichever is larger
>>>
>>> Yep I found this, I'd like to know this information at compile time.
>>
>> I actually found another way(1) but if someone knows how to get this
>> information at compile time I'm still interested. Thx !
>>
>> 1. https://github.com/D-Programming-Language/dmd/pull/4952
>
> real.sizeof ?
>

NVM

-- 
Dmitry Olshansky

On Tuesday, 25 August 2015 at 00:13:28 UTC, Xinok wrote:
> On Monday, 24 August 2015 at 21:55:40 UTC, Guillaume Chatelet wrote:
>> On linux x86_64 : real.sizeof == 16 but it looks like only the first the first 10 bytes are used (ie. 80bits)
>>
>> Is there a way to know the real size of a real ?
>
> The best I can think of is to use the mant_dig property which returns the number of bits in the mantissa.
>
> http://dpaste.dzfl.pl/9889b3d0bd5b

Thx for the proposal. I actually found this in std.math which confirms this is indeed a possibility.
https://github.com/D-Programming-Language/phobos/blob/6681862b4e3a77004e8d6ec1f62cf6587e20f6d4/std/math.d#L228