Re: [Boost-bugs] [Boost C++ Libraries] #6546: ratio_arithmetic/ratio_add_pass fails to compile

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #6546: ratio_arithmetic/ratio_add_pass fails to compile
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2018-04-25 09:20:04

#6546: ratio_arithmetic/ratio_add_pass fails to compile
-----------------------------------+------------------------------
  Reporter:  smr@…                 |      Owner:  Aleksey Gurtovoy
      Type:  Bugs                  |     Status:  new
 Milestone:  To Be Determined      |  Component:  mpl
   Version:  Boost Release Branch  |   Severity:  Problem
Resolution:                        |   Keywords:
-----------------------------------+------------------------------

Comment (by Matthijs Kooijman <matthijs@…>):

 This bug still seems to exist (I tried today's mpl git master). The
 essence, as indicated in the mailing list thread above, is that
 {{{mpl::integral_c}}} cannot support the minimum and maximum values of
 signed types, since the compiler does not allow defining the prior and
 next values, since that would cause signed overflow which is undefined.

 The error shown in the original report is about using ratio, but this bug
 can be easily reproduced on by instantiating {{{mpl::integral_c}}}
 directly:

 {{{
 #include <boost/mpl/integral_c.hpp>
 typedef boost::mpl::integral_c<int32_t,0x7fffffff>::type next_ovf_32;
 typedef boost::mpl::integral_c<int32_t,0x80000000>::type prior_ovf_32;
 typedef boost::mpl::integral_c<int64_t,0x7fffffffffffffff>::type
 next_ovf_64;
 typedef boost::mpl::integral_c<int64_t,0x8000000000000000>::type
 prior_ovf_64;
 }}}

 Which leads to these errors (only one of four shown).

 {{{
 In file included from foo.cpp:1:0:
 mpl/include/boost/mpl/aux_/integral_wrapper.hpp: In instantiation of
 ‘struct mpl_::integral_c<long int, -9223372036854775808l>’:
 foo.cpp:6:59:   required from here
 mpl/include/boost/mpl/aux_/integral_wrapper.hpp:73:88: warning: integer
 overflow in expression [-Woverflow]
      typedef AUX_WRAPPER_INST(
 BOOST_MPL_AUX_STATIC_CAST(AUX_WRAPPER_VALUE_TYPE, (value - 1)) ) prior;
 ~~~~~~~^~~~
 mpl/include/boost/mpl/integral_c.hpp:31:54: note: in definition of macro
 ‘AUX_WRAPPER_INST’
  #define AUX_WRAPPER_INST(value) AUX_WRAPPER_NAME< T, value >
                                                       ^~~~~
 mpl/include/boost/mpl/aux_/integral_wrapper.hpp:73:31: note: in expansion
 of macro ‘BOOST_MPL_AUX_STATIC_CAST’
      typedef AUX_WRAPPER_INST(
 BOOST_MPL_AUX_STATIC_CAST(AUX_WRAPPER_VALUE_TYPE, (value - 1)) ) prior;
                                ^~~~~~~~~~~~~~~~~~~~~~~~~
 In file included from mpl/include/boost/mpl/integral_c.hpp:32:0,
                  from foo.cpp:1:
 mpl/include/boost/mpl/aux_/integral_wrapper.hpp:73:96: error: overflow in
 constant expression [-fpermissive]
      typedef AUX_WRAPPER_INST(
 BOOST_MPL_AUX_STATIC_CAST(AUX_WRAPPER_VALUE_TYPE, (value - 1)) ) prior;
 ^~~~~
 mpl/include/boost/mpl/aux_/integral_wrapper.hpp:73:96: error: overflow in
 constant expression [-fpermissive]
 mpl/include/boost/mpl/aux_/integral_wrapper.hpp:73:96: note: in template
 argument for type ‘long int’
 }}}

 Solutions proposed in that thread are:
  - Convert to {{{intmax_t}}} before doing the +1 or -1. This is easy, but
 only fixes things for types smaller than {{{intmax_t}}}, leaves the
 problem for {{{intmax_t}}} and probably introduces the problem for
 {{{uintmax_t}}}. Post nr8 from Krzysztof Czainski in the above linked
 mailing list thread has an example implementation.
  - Specialize {{{integral_c}}} for these limiting values, leaving out the
 `next` or `prior` member. Post nr8 from Krzysztof Czainski in the above
 linked mailing list thread suggests this.
  - Remove the `next` and `prior` members from `integral_c` and use tag
 dispatch for them instead. Post nr4 by Vicente Botet in the above linked
 mailing list thread has a patch.

 #3779 seems to be a duplicate of this bug.

-- 
Ticket URL: <https://svn.boost.org/trac10/ticket/6546#comment:5>
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