Why is it that no one writes with portability in mind in druntime?

[IgorStepanov]

On Monday, 25 November 2013 at 22:54:03 UTC, Iain Buclaw wrote:
> On 25 November 2013 21:44, IgorStepanov <wazar at mail.ru> wrote:
>> On Sunday, 24 November 2013 at 11:38:27 UTC, Iain Buclaw wrote:
>>>
>>> https://github.com/D-Programming-Language/druntime/pull/663
>>
>>
>> This code is not portable only on CTFE part. (All those float 
>> manipulations
>> run at compile time)
>> I see three unportable aspects:
>> 1. This code supports only 80bit real. What other formats we 
>> need to
>> support? Can  the compiler support operations on those (or 
>> more precise)
>> formats? AFAIK dmd frontend perform all float operations in 80 
>> bit real and
>> supports only x86.
>
> The following IEEE 'real' formats are currently supported:
> 64 bit Big-endian  'double' (eg PowerPC)
> 128 bit Big-endian 'quadruple' (eg SPARC)
> 64 bit Little-endian 'double' (eg x86-SSE2)
> 80 bit Little-endian, with implied bit 'real80' (eg x87, 
> Itanium).
> 128 bit Little-endian 'quadruple' (not implemented on any known 
> processor!)
>
> Non-IEEE 128 bit Big-endian 'doubledouble' (eg PowerPC) has 
> partial support
>
> At least support for these is a must:
>
> version(LittleEndian)
> {
>     static assert(real.mant_dig == 53 || real.mant_dig==64
>                || real.mant_dig == 113);
> }
> else
> {
>     static assert(real.mant_dig == 53 || real.mant_dig == 113);
> }
>
> 128 bit doubledouble formats (real.mant_dig == 106) - are a 
> future goal.
>
>
>> 2. This code don't considers a float byte order. But compiler 
>> don't inform
>> user code about float BO. There are LittleEndian/BigEndian 
>> versions for
>> integers, but not for floats. You can add this versions on 
>> compiler and I'll
>> fix this aspect in druntime code.
>
> There doesn't exist a machine where the most significant byte 
> of a
> word is ordered differently to floats. See std.math if in 
> doubt, as
> this is already implemented.
>
>> 3. FloatTraits. Yes, thay works only with x86. Please, get 
>> link to other
>> supported float formats and I'll extend FloatTraits to those 
>> formats.
>>
>
> See std.math, which already has a cross-platform implementation 
> of
> that template with the same name (that amazingly existed years 
> ago).

I can't implement CTFE support of types more precise than x86 
80bit real. A think, all IEEE floats will be successfully 
processed like float and double (with same algorithm). But until 
CTFE don't support float with real.mant_dig>64 I can't process 
this types.
Resume: I'll modify FloatTraits, consider endianess and add 
assert(0) for too precise types.