Re: [Multiprecision] number conversion to __int128

From: A.Dmitrovsky (tdiff_at_[hidden])
Date: 2020-05-18 17:42:56

Sure, will file one. But could you please elaborate a bit, is it just a docs defect or something more?
 
Regards,
Anton
 
18.05.2020, 20:08, "John Maddock via Boost-users" <[e-mail]>:
> On 18/05/2020 17:32, A.Dmitrovsky via Boost-users wrote:
> >  Hi,
> >
> >  Strictly speaking, if I get it correct, that passage is about
> >  compatibility between different boost::multiprecision types (e.g.
> >  mp::int128 to mp::int256 conversion) and tells nothing about being
> >  able to convert to some other arithmetic type.
>
>
> Yes that's correct, like I said I thought I had this fixed, but
> apparently not fixed enough :(
>
> Can you please file a defect report on github so we don't forget?
>
> Thanks!  John.
>  
> >  So that's why I am here :)
> >  Regards,
> >  Anton
> >  18.05.2020, 16:51, "Paul A. Bristow via Boost-users"
> >  <[e-mail]>:
> >
> >
> >
> >      From: Boost-users <[e-mail]
> >      <mailto:[e-mail]>> On Behalf Of
> >      A.Dmitrovsky via Boost-users
> >      Sent: 15 May 2020 11:03
> >      To: [e-mail] <mailto:[e-mail]>
> >      Cc: A.Dmitrovsky <[e-mail] <mailto:[e-mail]>>
> >      Subject: [Boost-users] [Multiprecision] number conversion to __int128
> >
> >      Hi,
> >
> >      Boost::multiprecision docs [1] mentions that the type parameter of
> >      number::convert_to method should be "fundamental", pointing to the
> >      list of standard types ('A number can be converted to any
> >      https://en.cppreference.com/w/cpp/language/types type)'.
> >      This is different to number::convert_to reference [2], which
> >      states that "Type T may be any arithmetic type".
> >
> >      Can [unsigned] __int128 be treated as "fundamental" on
> >      compilers/platforms which support it?
> >
> >      [1]
> >      https://www.boost.org/doc/libs/1_73_0/libs/multiprecision/doc/html/boost_multiprecision/tut/conversions.html
> >      [2]
> >      https://www.boost.org/doc/libs/1_73_0/libs/multiprecision/doc/html/boost_multiprecision/ref/number.html
> >
> >      Does
> >
> >      “
> >        *Interconversions between number types of the same family are
> >      allowed and are implicit conversions if no loss of precision is
> >      involved, and explicit if it is:
> >        …
> >
> >      "
> >
> >      In
> >      https://www.boost.org/doc/libs/1_73_0/libs/multiprecision/doc/html/boost_multiprecision/tut/conversions.html
> >
> >      Not cover your case _uint128 ? and thus allowed for conversion.
> >
> >      Even if the _uint* and _int* types are not fundamental builtin
> >      types (regrettably - blame the glacial process of C and C++
> >      standardization and the millstone of C (don't ask) - but they
> >      might as well be for most purposes, including this one).
> >
> >      HTH
> >
> >      Paul
> >
> >
> >
> >
> >      _______________________________________________
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> >      [e-mail] <mailto:[e-mail]>
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> >
> >
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>  
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